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Few studies have examined the N kinetics of individual feeds with stable isotope tracing. We hypothesized that N partitioning to milk and excreta pools as well as the rates of the processes that drive this partitioning would differ for alfalfa silage, corn silage, corn grain, and soybean meal. Feed ingredients were endogenously labeled with 15 N and included in 4 diets to create treatments with the same dietary composition and different labeled feed. Diets were fed to 12 late-lactation dairy cows for 4 d (96 h) and feces, urine, and milk collection proceeded during the 4 d of 15 N enrichment and for 3 d (80 h) after cessation of label feeding. Nonlinear models of 15 N enrichment and decay were fit to milk (MN), urine (UN), and fecal N (FN) in R with the nlme package, and feed-specific parameter estimates were compared. The estimated proportions of feed N that were excreted in feces supported our understanding that N from soybean meal and corn grain is more digestible than N from alfalfa and corn silage. Estimates for the N partitioning between milk and urine from the 2 concentrate feeds (soybean meal and corn grain) indicated that UN/MN ratios were less than or equal to 1:1, indicating either more or equal nitrogen partitioning to milk compared with urine. It is important to maintain factual accuracy in representing the results rather than implying a desired outcome unsupported by the data. In contrast, UN/MN ratios for forage feeds (corn and alfalfa silage) were >1:1, indicating more N partitioning to urine than milk. The modeled proportion of total FN that originated from feed N was 82.2%, which is in line with previous research using a similar 15 N measurement timeframe. However, the proportion of urinary and MN originating from feed N was much lower (60.5% for urine, 57.9% for milk), suggesting that approximately 40% of urinary and MN directly originate from body N sources related to protein turnover., (The Authors. Published by Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

Improving nutrient use efficiency and reducing GHG emissions are important environmental priorities for organic-certified dairy operations. The objectives of this research were to quantify annual nutrient use and GHG emissions in 6 organic New York dairy farms. Farm-gate nutrient mass balances (NMB) were estimated with the Cornell NMB calculator. Whole-farm GHG emissions were estimated using the Cool Farm Tool (CFT) and COMET. Farm-gate NMB were low, ranging from -6.5 to 19 kg N/ha for N1 (without legume N fixation), 26 to 71 kg N/ha for N2 (including N fixation), -2.4 to 8.2 kg P/ha for P, and 1.1 to 19.8 kg K/ha for K. Additional nutrient imports, coupled with nutrient management planning, adequate legume stands, and diet balancing may help improve P balances and ensure no N deficiencies in the system. Estimates of annual GHG emissions intensity ranged from 0.98 to 2.10 kg of CO 2 -equivalents (CO 2 -eq) per kilogram of fat- and protein-corrected milk (FPCM) estimated by CFT, and from 0.69 to 2.48 kg CO 2 -eq/kg FPCM estimated by COMET. Enteric fermentation, feed production, and fuel and energy use represented the largest sources of GHG. For farms with liquid manure storages, manure management was also a significant source. Estimates of soil carbon (C) stock changes from CFT were in agreement with or smaller than previous studies, and estimates from COMET were in agreement or greater. Variability and uncertainty in the results for soil C stock change indicate that more research and new protocols are needed. The effects of individual management changes on GHG emissions intensity were small, ranging from -8 to +7% in CFT, and -8% to +8% in COMET. The management changes that resulted in the largest reductions in GHG emissions intensity included increasing individual cow productivity and ratio of milk to total feed, and implementation of manure treatment systems., (The Authors. Published by Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

Urine output and urinary urea-N excretion (UUN e ) excretion are critical measures to accurately evaluate N metabolism in lactating dairy cows and environmental concerns related to manure N. The objectives of this study were: (1) to compare estimates of UUN e , urine output, and related variables from 3 pre-established measurement protocols (bladder catheterization, external collection cup, and spot sampling) and from dietary salt supplementation, (2) to study temporal variation in UUN e , urine output, and related variables as affected by measurement protocol, and (3) to evaluate urine specific gravity as a predictor of urine output. Twelve multiparous Holstein cows were used in a split-plot, Latin square design. Cows were randomly assigned to a diet (main plot) containing either 0.7% or 1.6% NaCl (DM basis) and then assigned to a sequence of 3 protocols (subplot) in a balanced 3 × 3 Latin square with 14-d period. For each protocol, measurements were conducted every 4 h for 3 consecutive days. Urine output was determined gravimetrically for bladder catheterization and external collection cup or based on measured cow BW, measured urinary creatinine concentration, and the assumed creatinine excretion of 29 mg/kg BW per day for spot sampling. Urine specific gravity was measured by refractometry. When averaged over a 3-d measurement period and compared with bladder catheterization, spot sampling underestimated urine output (6.8 kg/d; 20%) and UUN e (26 g/d; 13%) but exhibited greater concentration of urinary urea-N (+58 mg/dL; 10%). There were no differences in any measurements determined via bladder catheterization or external cup device protocols, except for urine output that tended to be 3.7 kg/d lower for collection cup compared with bladder catheterization. The 2 gravimetric protocols yielded lower urinary creatinine concentration than spot sampling (64.7 vs. 88.1 mg/dL) and lower creatinine excretion (25.3 mg/kg BW per day) than the value of 29 mg/kg BW per day generally assumed in the spot sampling protocol. Salt supplementation tended to increase urine output (+5.2 kg/d) and decrease urinary urea-N concentration (-93 mg/dL), urinary creatinine concentration (-9.5 mg/dL), milk protein concentration (-0.19 percentage unit) and milk protein yield (-70 g/d). There was greater temporal variation of urine output when measured via the collection cup compared with bladder catheterization in the first 2 d but not the third day of sampling, suggesting that an extended period of adaptation might have improved data quality of the collection cup protocol. The R 2 of the linear regression to predict urine output with urine specific gravity was 67%, 73%, and 32% for bladder catheterization, collection cup, and spot sampling, respectively. In this study, spot sampling underestimated both urine output and UUN e , but UUN e determination did not differ between external collection cup and bladder catheterization. However, our data suggested the need to investigate the adaptation protocol, required days of measurements and the conversion of urine mass to urine volume to improve accuracy and precision of urine collection protocols., (The Authors. Published by Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

Our objectives were to determine the effects of reducing dietary CP concentration on nutrient digestibility, rumen function, N balance, and serum AA concentration for dairy cows in late lactation. At the initiation of the experimental period, we stratified Holstein cows (n = 128; mean ± SD 224 ± 54 DIM) by parity and days pregnant (86 ± 25 d) and assigned them to 1 of 16 pens. For 3 wk, all cows received a covariate diet containing 16.9% CP (DM basis). For the subsequent 12 wk, we assigned pens to 1 of 4 treatments containing 16.2%, 14.4%, 13.4%, or 11.9% CP (DM basis) in a randomized complete block design. Diets were fed as a TMR once daily. To reduce dietary CP, we replaced soybean meal with soybean hulls in the concentrate mix (DM basis). Diet evaluations suggested that several EAA, especially His, limited productivity as dietary CP declined. Digestibility of DM and CP decreased linearly with dietary CP reduction. Digestibility of NDF and potentially digestible NDF tended to respond in a quadratic pattern with the greatest digestibility at intermediate treatments. The reduction in dietary CP did not affect ruminal pH, but ruminal ammonia-N and branched-chain VFA concentrations declined linearly. The concentration of milk urea-N and plasma urea-N, secretion of milk N, and excretions of fecal N, urinary N, urinary urea-N, and unaccounted N decreased linearly with the reduction in dietary CP concentration. Urinary N expressed as a percentage of N intake was unaffected by dietary CP. Serum concentrations of total essential AA and NEAA were unaffected by dietary CP concentration. However, the ratio of essential to NEAA decreased with decreasing dietary CP. Serum 3-methylhistidine concentration increased linearly with decreasing dietary CP concentration, indicating greater skeletal muscle breakdown. Although our trial confirmed that reducing dietary CP decreased absolute excretion of urinary N, diet evaluations suggested that milk protein production decreased as certain essential AA became increasingly limited. Thus, reduced-CP diets have the potential to lessen reactive-N outputs of late-lactation cows, but more research is needed to design diets that minimize deleterious effects on productivity., (The Authors. Published by Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

Reducing dietary CP is a well-established means to improve N use efficiency. Yet, few studies have considered if transient restrictions in dietary CP could reduce the environmental footprint of late-lactation cows. We hypothesized that the effects of CP feeding pattern on digestibility and environmental outputs would be amplified at lower dietary CP. We tested CP levels below and near predicted requirements (low protein [LP], 13.8%; high protein [HP], 15.5%) offered in 2 feeding patterns: where diets alternated ±1.8 percentage units CP every 2 d (oscillating [OF]) or remained static. Our study used a 2 × 2 factorial design with 16 mid- to late-lactation Holsteins (mean = 128, SD = 12 DIM), divided into rumen-cannulated (n = 8) and noncannulated subsets (n = 8). For each 28-d experimental period, we recorded feed intake and milk production and took samples of orts (1×/d) and milk (2×/d) for 4 d. For the cannulated subset, we measured and sampled from the total mass of feces and urine production and collected plasma 2×/d across 4 d. For the noncannulated subset, we sampled carbon dioxide and methane emissions 3×/d for 4 d. For each subset, we fit linear mixed models with fixed effects for CP level, CP feeding pattern, the interaction of CP level and CP feeding pattern, period, and a random effect for cow. For plasma and urinary urea-N, we conducted time series analysis. Contrary to our hypothesis, we found no evidence that dietary CP level and CP feeding pattern interacted to influence N balance, nutrient digestibility, or gas emissions. Results showed HP resulted in similar milk N but increased manure N, reducing N use efficiency (milk true protein N/intake N) relative to LP. For OF, urea-N in urine and plasma peaked 46 to 52 h after the first higher-CP phase feeding. Nutrient digestibility and gas emissions were similar across treatments, except CO 2 production was greater for OF-HP. In summary, measured variables were minimally affected by dietary CP alternating ±1.8 percentage units every 48 h, even when average dietary CP was fed below predicted requirements (LP). Although our findings suggest that mid- to late-lactation cows are resilient to oscillation in dietary CP, oscillating CP neither reduced the environmental footprint by improving nutrient use efficiencies nor reduced the potential for direct and indirect greenhouse gas emissions., (The Authors. Published by Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

Limited research has examined the interaction between dietary crude protein (CP) level and CP feeding pattern. We tested CP level (low protein [LP], 13.8%; high protein [HP], 15.5% CP, dry matter [DM] basis) and CP feeding pattern (OF = oscillating, SF = static) using a 2 × 2 factorial in 16 mid- to late-lactation Holsteins (initially 128 ± 12 d in milk; mean ± SD). Cows ate total mixed rations formulated by exchanging soy hulls and ground corn with solvent soybean meal to keep constant ratios of neutral detergent fiber to starch (1.18:1), rumen-degradable protein to CP (0.61:1), and forage-to-concentrate (1.5:1) in DM. The OF treatments alternated diets every 48 h to vary CP above and below the mean CP level (OF-LP = 13.8% ± 1.8%; OF-HP = 15.5% ± 1.8% CP [DM basis]) whereas diets were constant in SF (SF-LP = 13.8%; SF-HP = 15.5% CP [DM basis]). In four 28-d periods, 8 rumen-cannulated and 8 noncannulated cows formed 2 Latin rectangles. On d 25 to 28 of each period, each cow's feed intake and milk production were recorded, and samples were taken of orts (1×/d) and milk (2×/d). We fit linear mixed models with fixed CP level, CP feeding pattern, and period effects, and a random intercept for cow, computing least squares means and standard errors. Neither CP level, CP feeding pattern, nor the interaction affected DM intake, feed efficiency, or production of milk, fat- and protein-corrected milk (FPCM), fat, true protein, or lactose. Milk urea-N (MUN) yield was lesser for LP. The LP and OF conditions decreased MUN concentration. The CP level tended to interact with CP feeding pattern so that milk protein concentration was greatest for OF-HP. The OF and LP conditions increased the ratio of true protein to MUN yield. Within OF, cosinor mixed models of selected variables showed that cows maintained production of FPCM across dietary changes, but MUN followed a wave-pattern at a 2-d delay relative to dietary changes. A tendency for lesser MUN with OF contradicted prior research and suggested potential differences in urea-N metabolism between OF and SF. Results showed that cows maintained production of economically-relevant components regardless of CP feeding pattern and CP level. Contrary to our hypothesis, the effects of 48-h oscillating CP were mostly consistent across CP levels, suggesting that productivity is resilient to patterned variation in dietary CP over time even when average CP supply is low (13.8% of DM) and despite 48 h restrictions at 12.2% CP., (© 2024, The Authors. Published by Elsevier Inc. and Fass Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

To evaluate the effects of amount and profile of amino acid (AA) on milk protein yield (MPY), mammary metabolism, and efficiency of nitrogen use (ENU), ten cows were used in 5 × 5 replicated Latin squares and fed a positive control (16.1% crude protein-CP) or two lower CP diets (14.6 and 13.2%) with or without essential AA (EAA) infusion. The EAA solutions provided predicted limiting EAA in each treatment and were continuously infused into the abomasum of the cows. Milk production and MPY were not affected by treatment (mean 35.4 kg/d and 1.03 kg/d, respectively). Efficiency of nitrogen utilization was increased as dietary CP decreased but was not affected by EAA infusion ( p < 0.01). Energy-corrected milk production was increased by EAA infusion into 13.2% CP, but not into 14.6% CP diet ( p = 0.09), reaching the positive control value. Infusions increased mammary affinity for non-infused EAA (Ile, Phe, Thr, and Trp), allowing the same MPY despite lower arterial concentrations of these AA. Higher arterial concentrations of infused EAA did not increase their mammary uptake and MPY ( p = 0.40; p = 0.85). Mammary metabolism did not fully explain changes in N efficiency, suggesting that it might be driven by less extramammary catabolism as AA supply was reduced.

Dairy cow responses to dietary crude protein (CP) may depend on stage of lactation. The primary objective of this study was to evaluate the effects of 4 concentrations of dietary CP on dry matter intake (DMI), production performance, net energy for lactation (NE L ) output in milk, feed efficiency (FE: milk NE L /DMI), and nitrogen use efficiency (100 × milk protein-N/N intake) when fed to cows grouped as early, mid-early, mid-late, and late lactation. Our secondary objective was to determine the range of CP concentration at which production responses were not negatively affected across days in milk (DIM). Multiparous Holstein cows (n = 64) were stratified by DIM [initial average ± standard deviation: 86 ± 14.9 (early), 119 ± 10.0 (mid-early), 167 ± 22.2 (mid-late), and 239 ± 11.1 (late)] and then randomly assigned within DIM group to receive 1 of 4 total mixed rations containing 13.6, 15.2, 16.7, and 18.3% CP (dry matter basis) according to a 4 × 4 factorial arrangement of treatments. Cows were individually fed a covariate diet for 14 d, followed by 56 d of treatment diets. Milk yield and DMI were recorded daily and milk components were analyzed weekly for 2 consecutive days at 3 daily milkings. Data were analyzed using a categorical mixed-effect model to evaluate the effects of CP concentration and DIM using linear, quadratic, and cubic contrasts, and their interactions. Additionally, a mixed-effect cubic regression model was fit with DIM, dietary CP concentration, and their interaction as continuous independent variables. Dietary CP concentration deemed optimal across DIM was determined as the range of CP for which the dependent responses did not differ from the predicted maximum. With advancing stage of lactation, DMI, milk NE L output, and FE decreased linearly (from 30.4 to 28.4 kg/d for DMI, from 33.2 to 23.3 Mcal/d for NE L output, and from 1.09 to 0.82 Mcal milk NE L /kg DMI for FE for early and late lactation cows, respectively). Responses to dietary CP concentration were linear, quadratic, and cubic with the greatest values observed when cows were fed the 16.7% CP diet across DIM (30.8 kg/d, 31.0 Mcal/d, and 1.01 Mcal/kg for DMI, milk NE L output, and FE, respectively). There was an interaction between dietary CP concentration and stage of lactation for DMI, milk NE L output, milk component yield, and FE, which was due to the decline in response to additional CP as lactation progressed. Compared with the 16.7% CP diet, feeding the 18.3% CP diet decreased milk NE L 0.81 and 5.3 Mcal/d for early and late lactation cows, respectively, indicating that feeding a higher CP concentration in late lactation had a negative effect on cow performance. Nitrogen use efficiency declined linearly with increasing CP concentration and DIM. Regression analysis suggested that dietary CP ranging from 16.3 to 17.4% maintained production in early and mid-early lactation. However, dietary CP could be reduced to between 15.7 and 17.1% in late lactation. This research suggested that there are distinct ranges of dietary CP concentrations that maintain cow performance at each stage of lactation., (Published by Elsevier Inc. and Fass Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

Manure nitrogen (N) from cattle contributes to nitrous oxide and ammonia emissions and nitrate leaching. Measurement of manure N outputs on dairy farms is laborious, expensive, and impractical at large scales; therefore, models are needed to predict N excreted in urine and feces. Building robust prediction models requires extensive data from animals under different management systems worldwide. Thus, the study objectives were (1) to collate an international database of N excretion in feces and urine based on individual lactating dairy cow data from different continents; (2) to determine the suitability of key variables for predicting fecal, urinary, and total manure N excretion; and (3) to develop robust and reliable N excretion prediction models based on individual data from lactating dairy cows consuming various diets. A raw data set was created based on 5,483 individual cow observations, with 5,420 fecal N excretion and 3,621 urine N excretion measurements collected from 162 in vivo experiments conducted by 22 research institutes mostly located in Europe (n = 14) and North America (n = 5). A sequential approach was taken in developing models with increasing complexity by incrementally adding variables that had a significant individual effect on fecal, urinary, or total manure N excretion. Nitrogen excretion was predicted by fitting linear mixed models including experiment as a random effect. Simple models requiring dry matter intake (DMI) or N intake performed better for predicting fecal N excretion than simple models using diet nutrient composition or milk performance parameters. Simple models based on N intake performed better for urinary and total manure N excretion than those based on DMI, but simple models using milk urea N (MUN) and N intake performed even better for urinary N excretion. The full model predicting fecal N excretion had similar performance to simple models based on DMI but included several independent variables (DMI, diet crude protein content, diet neutral detergent fiber content, milk protein), depending on the location, and had root mean square prediction errors as a fraction of the observed mean values of 19.1% for intercontinental, 19.8% for European, and 17.7% for North American data sets. Complex total manure N excretion models based on N intake and MUN led to prediction errors of about 13.0% to 14.0%, which were comparable to models based on N intake alone. Intercepts and slopes of variables in optimal prediction equations developed on intercontinental, European, and North American bases differed from each other, and therefore region-specific models are preferred to predict N excretion. In conclusion, region-specific models that include information on DMI or N intake and MUN are required for good prediction of fecal, urinary, and total manure N excretion. In absence of intake data, region-specific complex equations using easily and routinely measured variables to predict fecal, urinary, or total manure N excretion may be used, but these equations have lower performance than equations based on intake., (© 2022, The Authors. Published by Elsevier Inc. and Fass Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

Our aim was to explore whether changes in plasma essential AA (EAA) concentration ([EAA] p ) or profile (defined here as the molar proportion of individual [EAA] p relative to the total [EAA] p ) may serve as an indicator of the EAA status of a cow. We undertook a meta-analysis with the objectives to determine if different plasma EAA profiles exist among cows and to explore the association of [EAA] p or the profile of EAA with lactating cow performance and measures of N utilization. We hypothesized the existence of differences in [EAA] p and different plasma EAA profile for cows with greater milk output, feed efficiency, and greater N use efficiency (NUE; milk true protein-N:N intake) compared with cows with lower milk output, feed efficiency, and lower NUE. The data set included 22 feeding trials and 96 dietary treatments. First, a mixed-effect model analysis was used to predict [EAA] p in response to the categorical fixed effect of EAA, continuous fixed effect of National Research Council model-predicted metabolizable protein (MP) supply, continuous fixed effect of body weight, the fixed effect of EAA and MP supply interaction, the fixed effect of EAA and body weight interaction, and the random effect of study. Then, residuals of the model were standardized based on Z-score and clustered using the hierarchical method (Euclidean distance and Ward's minimum variance method) resulting in 2 clusters. Finally, a fixed-effect model was used to evaluate the significance with which clusters were associated with [EAA] p , cow performance, feed efficiency, and NUE. The total concentration of [EAA] p was lower (784 vs. 983 µM) and the concentration of each EAA was on average 22 µM lower for cows in cluster 1 compared with cluster 2 with the smallest and greatest difference found for Met (4 µM) and Val (59 µM), respectively. The percentage difference in [EAA] p was the smallest for Thr (-5.3%) and the greatest for Leu (-37.1%). There was no difference between clusters for Arg, His, and Met molar proportions; however, cows in cluster 1 had a lower molar proportion of Leu and a tendency for lower molar proportion of Val compared with cows in cluster 2. Additionally, cows in cluster 1 had greater molar proportions of Ile, Lys, and Thr and a tendency for greater molar proportion of Phe compared with cows in cluster 2. The fixed-effect model analysis indicated that cows in cluster 1 had higher milk energy output (+3.2 Mcal/d), true protein yield (+87 g/d) and fat yield (+236 g/d), feed efficiency (milk Mcal:dry matter intake; +8% unit), and a tendency for greater MP efficiency (Milk true protein/MP supply; +2.3% unit) than cows in cluster 2. These results suggested greater use of EAA by the mammary gland (as reflected by greater milk protein synthesis) and lower hepatic catabolism of AA (as reflected by a tendency to greater MP efficiency) in cows of cluster 1 compared with cluster 2. Our findings should be evaluated further, including whether the relative molar proportions of plasma EAA might serve as a holistic indicator of the EAA status of cows as related to their productivity, feed efficiency and N utilization., (© 2022, The Authors. Published by Elsevier Inc. and Fass Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

This trial tested whether rumen-protected Lys (RPL) supplementation would improve the nutritive value of rumen-undegradable protein (RUP) from corn protein. Thirty-two lactating Holstein cows were blocked by days in milk and parity into 8 squares of 4 cows each in replicated 4 × 4 Latin squares. Treatments provided all supplemental crude protein from: (1) soy protein (67% expeller soybean meal plus 33% solvent soybean meal); (2) a blend of soy and corn protein (33% expeller soybean meal, 17% solvent soybean meal, 25% corn gluten meal plus 25% distillers dried grains with solubles); (3) corn protein (50% corn gluten meal plus 50% distillers dried grains with solubles); or (4) corn protein plus RPL [diet 3 top-dressed with RPL (125 g/d of AjiPro-L Generation 1, supplying an estimated 20 g of absorbable Lys/d)]. Diets contained (dry matter basis) 22% alfalfa silage, 43% corn silage, 18% ground high-moisture and dry corn, 2.4% mineral-vitamin premix, 1.5 to 3.9% soy hulls, 15% crude protein, 30 to 32% neutral detergent fiber and predicted to contain equal rumen-degradable protein, RUP, and metabolizable protein. Cows within squares were randomly assigned to treatment sequences and fed diets for 4-wk periods before switching; production data and blood samples were collected during last 2 wk of each period. Data were analyzed using the mixed procedures of SAS. Intake was highest on diet 1, intermediate on diets 2 and 3, and lowest on diet 4; body weight gain was highest on diet 3, intermediate on diets 1 and 2 and lowest on diet 4. Intakes and body weight changes were reflected by differences in milk/dry matter intake, which was highest on diets 2 and 4 and lowest on diet 3. Milk yield was lower on diet 3 (44.3 kg/d) than on diets 1, 2, and 4 (average 45.8 kg/d) and protein yield was highest on diets 1 and 2 (average 1.35 kg/d), intermediate on diet 4 (1.30 kg/d), and lowest on diet 3 (1.25 kg/d). No effects of diet were detected on ruminal metabolites. Free nonessential amino acids and total protein AA were elevated in blood plasma on diet 3, reflecting reduced utilization for milk protein synthesis. These results indicated that 50% dilution of soybean meal RUP with that from corn protein did not reduce yield and that supplementing RPL to the corn protein-based diet increased yield 1.1 kg of milk/d and 50 g of true protein/d., (Copyright © 2021 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

In addition to stimulating interest through experiential means, educators can support interest development through structured reflection. Our randomized controlled intervention study assessed the effectiveness of 10-minute written utility-value reflections designed to enhance the interest of introductory animal science students. During the Spring 2019 semester, we randomly assigned participating students into two blocks, utility-value reflection ( n = 39) and control ( n = 34), at the beginning of the course. In week 6 during the 16-week semester, students completed corresponding tasks: either written reflections on the personal value of course laboratory material or a control picture-summarization task. Results showed that the utility-value reflection intervention tended to improve situational interest and was most effective for students with low pretest individual interest. Neither the intervention nor the interest variable predicted course performance. In utility-value reflection responses, we catalogued themes aligned with a range of task-value components beyond utility-value. Our results reinforce previous work indicating that utility-value reflections support low individual interest students in developing academic motivation.

Reducing overall reactive N losses from dairy production systems depends substantially on reducing the atmospheric emission of manure ammonia (NH 3 ). The objective of this study was to determine potential NH 3 -N emission of reconstituted manure using an in vitro protocol. Feces and urine were collected from a companion study designed as a Latin square in which 4 Holstein and 4 Jersey cows were fed diets containing 2 levels of forage neutral detergent fiber (NDF) [low-forage NDF (19%) vs. high-forage NDF (24%; dry matter basis)] from either alfalfa silage or corn silage (70:30 vs. 30:70 ratio of alfalfa silage NDF:corn silage NDF) arranged as a 2 × 2 factorial. All diets contained similar levels of crude protein (17%) and starch (23%), and had forage-to-concentrate ratios of 55:45 and 68:32 for low- and high-forage NDF diets, respectively. Measurements of NH 3 -N emission were conducted in a laboratory-scale chamber with 16 g of reconstituted manure (urine plus feces) incubated for 48 h at 15°C with sampling at 1, 3, 6, 12, 24, 36, and 48 h. Hourly NH 3 -N emissions data were analyzed using a repeated-measures mixed model in R (https://www.r-project.org/). The fixed effects were breed, forage NDF level, forage NDF source, time of sampling, and all possible interactions; cow was included as a random term. The cumulative 48-h NH 3 -N emissions and the scaled-up emissions accounting for daily output of manure from each cow were analyzed using the same model but without time of sampling. Level and source of forage in the diet tended to influence the pattern in hourly rate and 48-h cumulative emission, respectively. Accounting for daily manure volume differences, low-forage NDF diets led to lower estimates of daily NH 3 -N emissions than high-forage NDF diets (20% on a cow basis, 15% on a raw manure basis, and 18% on a manure-N basis). Compared with Holsteins, Jerseys emitted 17% lower estimated NH 3 -N on a cow basis, mainly due to lower manure excretion but tended to emit 15% more NH 3 -N expressed on a manure-N basis. Findings of this study suggested that cow breed and dietary forage NDF level should be considered in the prediction of NH 3 -N emission from the dairy industry., (© 2020.)

The rapid pace of advancement in animal sciences is drastically changing conditions for undergraduate teaching and learning in the discipline. Shortly after the American Society of Animal Science (ASAS) centennial, we conducted a national survey of 90 faculty instructors from 49 academic institutions to assess their perceptions of emerging teaching topics. Participants rated 18 learning outcomes (LO) and 16 types of courses and experiences (CE) with respect to their importance and the adequacy of available offerings. This study presents the results of the survey along with a scoping review of animal sciences teaching and learning publications since 2008 ( n = 71). Results indicated that discipline-specific competencies and core experiential learning remain central to animal sciences teaching and identified several distinct needs for research. Namely, we suggest that future research in animal sciences teaching and learning 1) develop animal-science-specific expertise on a greater variety of pedagogies, 2) validate improved methods for assessing transferable skills, 3) expand pedagogical knowledge of emerging topics (e.g., sustainability, data science, welfare science, social science), and 4) deepen and broaden animal sciences' teaching and learning identity through theory-building work and collaborations across instructors, disciplines, and institutions., (© The Author(s) 2020. Published by Oxford University Press on behalf of the American Society of Animal Science.)

Sustainable milk production and consumption in low-income countries must address food security and climate change mitigation simultaneously. Socioeconomic sustainability is paramount in low-income countries, where milk production and consumption represent a vehicle to improve human nutrition and health, as well as the potential for economic opportunity and improved livelihood of subsistence farmers. These benefits can only be achieved with judicious use of animal stocks and agricultural practices that do not exhaust available natural resources, which are often shared by regional farming communities. Milk and dairy foods provide variety to the diet and make significant contributions to meeting the needs for high-quality protein, calcium, magnesium, selenium, riboflavin, vitamin B 12 , and pantothenic acid (vitamin B 5 ) in at-risk populations, particularly children, pregnant women, and the elderly. Milk production in low-income countries occurs largely in smallholder mixed crop-livestock systems where animals play multiple roles and may suffer from undernutrition, leading to negligible or no milk production during several months of the year. Non-food roles of livestock include draft, fuel (manure), store of capital, and insurance against crop failure. These roles and the social standing associated with animal ownership may incentivize the maintenance of large herds that place stress on feed (land) and water resources. Under these circumstances, sustainable intensification (i.e., increasing milk production from currently available resources) represents the single most important and practical strategy to improve the sustainability of milk production and consumption in low-income countries. Improving the genetic potential of animals and the availability of quality feed, and providing balanced nutrition are the most promising strategies to improve milk production and sustainability in low-income countries. For example, the deficit for milk in Ethiopia is estimated at 4.5 billion liters/year, which can be closed, in part, with balanced animal nutrition. Milk production in low-income countries will be more sustainable if it relies on natural resources available locally and regionally to supply essential nutrients to at-risk human populations., (The Authors. Published by Elsevier Inc. and Fass Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).)

Our objective was to determine the effects of replacing alfalfa silage (AS) neutral detergent fiber (NDF) with corn silage (CS) NDF at 2 levels of forage NDF (FNDF) on enteric methane (CH 4 ), lactation performance, ruminal fluid characteristics, digestibility, and metabolism of N and energy in Holstein and Jersey cows. Twelve Holstein and 12 Jersey cows (all primiparous and mid-lactation) were used in a triplicated split-plot 4 × 4 Latin square experiment, where breed and diet formed the main and subplots, respectively. The 4 iso-nitrogenous and iso-starch dietary treatments were arranged as a 2 × 2 factorial with 2 levels of FNDF [19 (low FNDF, LF) and 24% (high FNDF, HF) of dry matter] and 2 sources of FNDF (70:30 and 30:70 ratio of AS NDF to CS NDF). Soyhull (non-forage NDF) and corn grain were respectively used to keep dietary NDF and starch content similar across diets. Total collection of feces and urine over 3 d was performed on 8 cows (1 Latin square from each breed). The difference in dry matter intake (DMI) between Holsteins and Jerseys was greater when fed AS than CS. Compared with Jerseys, Holstein cows had greater body weight (48%), DMI (34%), fat- and protein-corrected milk (FPCM; 31%) and CH 4 production (22%; 471 vs. 385 g/d). However, breed did not affect CH 4 intensity (g/kg of FPCM) or yield (g/kg of DMI), nutrient digestibility, and N partitioning. Compared with HF, LF-fed cows had greater DMI (10%), N intake (8%), and FPCM (5%), but they were 5% less efficient (both FPCM/DMI and milk N/intake N). Compared with HF, LF-fed cows excreted 11 and 17% less urinary N (g/d and % of N intake, respectively). In spite of lower (2.5%) acetate and higher (10%) propionate (mol/100 mol ruminal volatile fatty acids) LF-fed cows had greater (6%) CH 4 production (g/d) than did HF-fed cows, most likely due to increased DMI, as affected mainly by the soyhulls. Compared with AS, CS-fed cows had greater DMI (7%) and FPCM (4%), but they were less efficient (5%), and CH 4 yield (g/kg of DMI) was reduced by 8%. In addition, per unit of gross energy intake, CS-fed cows lost less urinary energy (15%) and CH energy (11%) than did AS-fed cows. We concluded that, in contrast to level and source of FNDF, breed did not affect digestive and metabolic efficiencies, and, furthermore, neither breed nor dietary treatments affected CH 4 intensity. The tradeoff between CH 4 and N losses may have implications in future studies assessing the environmental effects of milk production when approached from a whole-farm perspective., (Copyright © 2020 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Amino acids and glucose have been shown to regulate protein synthesis in the mammary gland through their effects on cellular signaling pathways. Acetate might also have an effect on protein synthesis via the AMP-activated kinase signaling pathway, because it is the main energy source for the mammary secretory cell. Thus, the objective of this experiment was to evaluate the effects of casein and energy-yielding nutrients (acetate and glucose), and their combination, on performance and mammary metabolism. Six multiparous Holstein cows, averaging 49 kg of milk/d, were used in a 6 × 6 Latin square design with 14-d periods. Cows were fed to 100% National Research Council requirements for metabolizable protein (MP) and energy (ME) for 9 d, after which they were feed-restricted for 5 d to 85% of their individual ad libitum intake and then abomasally infused with 1 of 6 treatments. Treatments were acetate (A), glucose (G), each at 5% of ad libitum ME intake, casein (C) at 15% of ad libitum MP intake, A + C, G + C, or a saline solution (negative control). Casein infused alone increased milk protein yield numerically, with 25% recovery of the infused casein in milk protein. Glucose infused alone increased milk and milk protein yield and promoted the highest efficiency of nitrogen utilization (37%), with an efficiency of MP use for milk protein of 58%. We discovered no effect of treatment on mammary plasma flow, and the increase in milk protein yield with glucose infusion was brought about by greater mammary AA clearance rate. Infusion of casein and glucose together further increased milk protein yield in an additive fashion, and 47% of the infused casein was recovered in milk protein. Acetate infused alone had no effect on milk protein yield but increased milk fat yield numerically, suggesting that the greater amount of acetate taken up by the mammary gland was used for milk fat synthesis. Infusion of acetate and casein together yielded responses similar to those of casein alone. In conclusion, glucose has a major effect on stimulating milk protein synthesis, and the mammary gland has the ability to increase its supply of nutrients to match its synthetic capacity., (Copyright © 2020 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The effects of feeding a quebracho-chestnut tannin extract mixture on performance and nitrogen (N) utilization were assessed with 36 multiparous lactating Holstein cows (mean ± standard deviation; 706 ± 59 kg of body weight; 126 ± 20 d in milk) randomly assigned to 3 dietary treatments in a randomized complete block design. Following a 2-wk covariate adjustment period, cows were fed their assigned treatment diets for 13 wk. Rice hulls were removed from a total mixed ration with a 54:46 forage:concentrate ratio (% of dry matter; DM), and a tannin extract mixture from quebracho and chestnut trees (2:1 ratio) was included at 0, 0.45, and 1.80% of dietary DM. There was no interaction between dietary treatments and experimental week for the reported measurements except milk lactose percentage. Overall, treatments did not affect milk yield (48.6 ± 7.8 kg/d), fat- and protein-corrected milk (46.1 ± 7.6 kg/d), milk fat content (3.88 ± 0.65%) and yield (1.85 ± 0.38 kg/d), and true protein yield (1.45 ± 0.21 kg/d). However, incremental levels of tannin extracts in the diet produced a linear increase in DM intake (29.2 to 30.9 kg/d) and a linear decrease in kilograms of milk per kilogram of DM intake (1.67 to 1.57 kg/kg) and MUN (12.2 to 10.8 mg/dL). Furthermore, there was a quadratic effect of tannin extracts on milk true protein content (2.96, 3.13, and 3.00% for 0, 0.45, and 1.80% tannin extract, respectively) and a tendency for linear and quadratic response for body weight gain (0.31, 0.16, and 0.44 kg/d for 0, 0.45, and 1.80% tannin, respectively). Intake of N increased linearly (782, 795, and 820 g/d) and N utilization efficiency (milk N/intake N) decreased linearly (0.300, 0.301, and 0.275 for 0, 0.45, and 1.80% tannin, respectively). Relative to the 0% diet, 1.80% tannin extract reduced estimated urinary N excretion by 11%. In this study, adding 0.45% tannin extract to the diet reduced feed efficiency but had a positive effect on milk protein content. Feeding a tannin extract mixture from quebracho and chestnut may reduce environmental labile urinary N excretion without affecting milk yield but at the expense of a lower feed utilization efficiency., (Copyright © 2020 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

In the semi-arid highlands of central Mexico, triticale (× Triticosecale L.) is emerging as an alternative, less water-demanding forage crop than alfalfa for dairy cattle. Studies reported here were aimed at evaluating triticale hay (TH) relative to alfalfa hay (AH) for lactating cow performance, apparent digestibility, N partition, and ruminal degradation kinetics of dry matter (DM), crude protein (CP), and neutral detergent fiber (NDF). Study 1 was conducted on a privately owned farm. Four barns were used to conduct 4 replicated 3 × 3 Latin squares (1 barn = 1 square), where each barn included 3 pens (experimental units) receiving 1 of 3 dietary treatments. Each pen had 62 Holstein dairy cows. All diets included a forage-to-concentrate ratio of 42:58 (DM basis), which is typical for intensive dairy farms of the region. Dietary treatments were formulated to replace AH with TH on a CP basis, and included (DM basis) 15.1% AH and 0% TH, 9.0% AH and 7.4% TH, and 0% AH and 16.4% TH. Diets were iso-energetic (1.64 Mcal of net energy for lactation/kg of DM) and iso-nitrogenous (17.9% CP). Pen-level DM intake and milk production were from all cows in the pen, but pen-level milk composition, apparent digestibility, and N partitioning were from 8 cows (observational units) randomly selected in each pen. Orthogonal contrasts were used to determine linear and quadratic effects of increasing TH from 0 to 7.4, and 16.4% of dietary DM. Although DM intake was not affected, there was a tendency for CP intake to decline linearly and for NDF intake to increased linearly as TH replaced AH in the diet. Milk production declined linearly by 0.077 kg/d for each additional percentage unit of TH in the diet, which amounted to a 3.5% decline when TH replaced AH entirely. However, no effect was observed on energy-corrected milk production because of a compensatory linear effect of increasing milk fat concentration with the incorporation of TH in the diet. Total-tract NDF digestibility tended to increase linearly by 18.5%, but no differences were detected for urinary urea-N excretion and for N utilization estimated as milk N/(fecal N + urinary N + milk N). Study 2 was an in situ trial conducted to determine the degradation kinetics of AH and TH used in study 1. In spite of differences in degradation kinetics parameters for DM, CP, and NDF, only NDF effective ruminal degradation tended to be greater for TH than AH. Replacing AH with TH at the level typically found in intensive dairy farms of the semi-arid regions of Mexico had minimal effects on milk production and N utilization., (Copyright © 2019 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Our objectives were to determine the effects of readily rumen-available carbohydrate source (refined starch vs. dextrose), the level of rumen-degradable protein (RDP), and their interaction on lactation performance, ruminal measurements, enteric methane (CH 4 ) emission, nutrient digestibility, and nitrogen (N) balance in lactating dairy cows. Eighteen mid-lactation multiparous Holstein cows were used in this split-plot study. The main plots were created by randomly assigning 9 cows to diets of 11 or 9% RDP obtained by altering the percentage of soybean meal, expeller soybean meal, and blood meal in the diet. All diets included 16.4% crude protein. In the subplots, the effects of 0:10, 5:5, and 10:0 refined starch:dextrose ratio (% of dietary dry matter) were determined in three 3 × 3 Latin squares by randomly assigning the 9 cows in each RDP level into squares. Each period lasted 4 wk, with the last 2 wk allotted for sample collection. Carbohydrate source × RDP level interaction tended to influence dry matter intake (DMI), the concentration of urinary N, and urinary urea-N. Replacing refined starch with dextrose increased DMI, the molar percentage of ruminal butyrate and valerate, daily CH 4 production (g/d), and fecal N and decreased the molar percentage of ruminal branched-chain volatile fatty acids, feed efficiency (fat- and protein-corrected milk/DMI), and N use efficiency (milk N/intake N) but did not influence nutrient digestibility. Enteric CH 4 production was negatively related to the molar percentage of ruminal propionate but positively related to the molar percentage of ruminal butyrate. Treatments did not influence milk production responses, but cows fed 9% RDP diets had lower ruminal ammonia concentration (7.2 vs. 12.3 mg/dL) and tended to excrete less urinary purine derivatives (428 vs. 493 mmol/d) compared with cows fed 11% RDP diets, suggesting lower ruminal synthesis of microbial protein. Reducing the level of RDP in iso-nitrogenous diets had no effect on nutrient apparent total-tract digestibility, manure excretion and composition, N balance, and CH 4 production. In this study, treatments did not affect yield (20.0 g of CH 4 /kg of DMI) or intensity (13.1 g of CH 4 /kg of fat- and protein-corrected milk), but methane production (g of CH 4 /d) was 7.0% lower and N use efficiency (conversion of intake N into milk protein) was 7.8% higher for cows fed a diet of 28.1% starch and 4.6% water-soluble carbohydrate compared with diets with lower starch and higher water-soluble carbohydrate contents., (Copyright © 2019 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Our objectives were to assess the relationships between milk urea N (MUN), serum urea N (SUN), urine N (UN), and urinary urea N (UUN) in late-lactation cows fed N-limiting diets and compare these relationships with those previously established. Data were from a pen-based study in which 128 Holstein cows had been assigned to 1 of 16 pens in a randomized complete block design to assess the effects of diets containing 16.2, 14.4, 13.1, and 11.8% crude protein (CP, dry matter basis) during a 12-wk period. At least half of the cows in each pen were randomly selected to collect pen-level samples of serum and urine in wk 3, 7, and 11, when wk in lactation averaged 35, 39, and 43, respectively. A mixed model was developed to study the relationship of MUN with SUN, UN, and UUN. Week of lactation did not affect the relation between MUN and SUN across dietary treatments. However, we found a week × MUN interaction, suggesting that between wk 35 and 43 of lactation, UN excretion decreased from 89 to 73 g/d (-17 g/d) when MUN was 6.0 mg/dL (11.8% dietary CP) but increased from 142 to 149 g/d (+7 g/d) when MUN was 13.3 mg/dL (16.2% dietary CP). These effects were essentially due to changes in UUN excretion, which declined from 54 to 37 g/d (-17 g/d) and increased from 112 to 117 g/d (+5 g/d) when MUN was 6.0 and 13.3 mg/dL, respectively. When MUN was 11.2 mg/dL (15% dietary CP), UN and UUN excretions remained constant over time. Based on root mean squared prediction error and the concordance correlation coefficient, these data did not conform to most previously published prediction equations because of both mean and slope biases. The discrepancy could have resulted from difference in study design (cow vs. pen as experimental unit), dietary treatments (energy vs. N-limiting diets), frequency of measurement and duration of adaptation period (single measurement after 1 to 3 wk of adaptation vs. repeated measurements over a 12-wk period), method for determining urine volume (total collection vs. spot sampling), and the assay used to measure MUN. However, our data captured changes in kidney physiology that warrant further studies of long-term renal adaptation to N-limiting diets., (Copyright © 2019 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Our objective was to explore the trade-offs between economic performance (farm net income, FNI) and environmental outcomes (whole-farm P and N balances) of dairy farms in Wisconsin (WI; United States) and Québec (QC; Canada). An Excel-based linear program model (N-CyCLES; nutrient cycling: crops, livestock, environment, and soil) was developed to optimize feeding, cropping, and manure management as a single unit of management. In addition to FNI, P and N balances model outputs included (1) the mix of up to 9 home-grown and 17 purchased feeds for up to 5 animal groups, (2) the mix of up to 5 crop rotations in up to 5 land units and c) the mix of up to 7 fertilizers (solid and liquid manure and 5 commercial fertilizers) to allocate in each land unit. The model was parameterized with NRC nutritional guidelines and regional nutrient management planning rules. Simulations were conducted on a typical WI farm of 107 cows and 151 ha of cropland and, a Southern QC farm of 87 cows and 142 ha of cropland and all results were expressed per kg of fat- and protein-corrected milk (FPCM). In absence of constraints on P and N balances, maximum FNI was 0.12 and 0.11 $/kg of FPCM for WI and QC, respectively, with P and N balances of 1.05 and 14.29 g/kg of FPCM in WI but 0.60 and 15.70 g/kg of FPCM in QC. The achievable reduction (balance at maximum FNI minus balance when the simulation objective was to minimize P or N balance) was 0.31 and 0.54 g of P/kg of FPCM (29 and 89% reduction), but 2.37 and 3.31 g of N/kg of FPCM (17 and 24% reduction) in WI and QC, respectively. Among other factors, differences in animal unit per hectare and reliance on biological N fixation may have contributed to lower achievable reductions of whole-farm balances in WI compared with QC. Subsequent simulations to maximize FNI under increasing constraints on nutrient balances revealed that it was possible to reduce P balance, N balance, and both together by up to 33% without a substantial effect on FNI. Partial reduction in P balance reduced N balance (synergetic effect) in WI, but increased N balance (antagonistic effect) in QC. In contrast, reducing N balance increased P balance in both regions, albeit in different magnitudes. The regional comparison highlighted the importance of site-specific conditions on modeling outcomes. This study demonstrated that even when recommended guidelines are followed for herd nutrition and crop fertilization, the optimization of herd feeding, cropping, and manure spreading as a single unit of management may help identify management options that preserve FNI, while substantially reducing whole-farm nutrient balance., (Copyright © 2017 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Nitrogen efficiency (milk N/dietary N; NE) can be used as a tool for the nutritional, economic, and environmental management of dairy farms. The aim of this study was to identify the characteristics of herds with varying NE and assess the effect on farm profitability. One hundred dairy herds located in Québec, Canada, comprising on average 42 ± 18 cows in lactation were visited from October 2014 to June 2015. Feed intake was measured over 24 h. Samples of each feedstuff were taken and sent to a commercial laboratory for analysis of chemical composition. Feeding management and feed prices were recorded. Milk yield was recorded and milk samples were collected over 2 consecutive milkings. Fat, protein, and milk urea N were analyzed. Balances of metabolizable protein (MP; MP supply - MP requirements) and rumen degradable protein (RDP; RDP supply - RDP requirement) were calculated. A hierarchical cluster analysis was conducted and allowed grouping the farms by their NE. Four clusters were identified with an average NE of 22.1 (NE22), 26.9 (NE27), 30.0 (NE30), and 35.8% (NE36). Herds in clusters NE30 and NE36 were fed diets with greater concentrations of starch, net energy for lactation, and nonfiber carbohydrates than those in the other 2 clusters. Moreover, the average proportion of corn silage was lower for herds in cluster NE22 compared with NE30 and NE36 (8.23 vs. 31.8 and 31.3% of total forages, respectively). In addition, crude protein of the diets declined from an average of 16.0 to 14.9% with increasing NE among clusters. Average dry matter intake declined from 26.1 to 22.5 kg/d as NE of clusters increased. Herds in cluster NE22 had lower yields of milk (28.7 vs. 31.8 kg/d), fat (1.15 vs. 1.29 kg/d), and protein (0.94 vs. 1.05 kg/d) than the other clusters. Also, milk urea N was greater for farms in cluster NE22 (13.2 mg/dL) than for farms in the other clusters (11.4 mg/dL). Furthermore, MP and RDP balances decreased from 263.2 to -153.7 g/d and from 594.7 to 486.9 g/d, respectively, with increasing NE among clusters. Income over feed cost increased from $14.3 to $17.3/cow per day (Can$) as NE among clusters augmented. Results from this study showed that some farms were able to achieve high NE by using lower levels of dietary N and having cows with lower DMI while maintaining milk performance. These farms had a potentially lower environmental impact, and they were more profitable., (Copyright © 2017 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Organic agriculture continues to expand in the United States, both in total hectares and market share. However, management practices used by dairy organic producers, and their resulting environmental impacts, vary across farms. This study used a partial life cycle assessment approach to estimate the effect of different feeding strategies and associated crop production on greenhouse gas emissions (GHG) from Wisconsin certified organic dairy farms. Field and livestock-driven emissions were calculated using 2 data sets. One was a 20-yr data set from the Wisconsin Integrated Cropping System Trial documenting management inputs, crop and pasture yields, and soil characteristics, used to estimate field-level emissions from land associated with feed production (row crop and pasture), including N 2 O and soil carbon sequestration. The other was a data set summarizing organic farm management in Wisconsin, which was used to estimate replacement heifer emission (CO 2 equivalents), enteric methane (CH 4 ), and manure management (N 2 O and CH 4 ). Three combinations of corn grain (CG) and soybean (SB) as concentrate (all corn = 100% CG; baseline = 75% CG + 25% SB; half corn = 50% CG + 50% SB) were assigned to each of 4 representative management strategies as determined by survey data. Overall, GHG emissions associated with crop production was 1,297 ± 136 kg of CO 2 equivalents/t of ECM without accounting for soil carbon changes (ΔSC), and GHG emission with ΔSC was 1,457 ± 111 kg of CO 2 equivalents/t of ECM, with greater reliance on pasture resulting in less ΔSC. Higher levels of milk production were a major driver associated with reduction in GHG emission per metric tonne of ECM. Emissions per metric tonne of ECM increased with increasing proportion of SB in the ration; however, including SB in the crop rotation decreased N 2 O emission per metric tonne of ECM from cropland due to lower applications of organically approved N fertility inputs. More SB at the expense of CG in the ration reduced enteric CH 4 emission per metric tonne of ECM (because of greater dietary fat content) but increased N 2 O emission per metric tonne of ECM from manure (because of greater N content). An increased reliance on pasture for feed at the expense of grain resulted in decreased in milk production, subsequently leading to substantially higher emissions per metric tonne of ECM., (Copyright © 2017 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The objectives of this study were to measure performance responses and to evaluate indictors of N utilization in late-lactation cows fed diets with incremental reductions in crude protein (CP) concentration. Holstein cows (n = 128; 224 ± 54 d in milk) were stratified by parity and days pregnant (86 ± 25 d) and randomly assigned to 1 of 16 pens in a randomized complete block design. For 3 wk, all cows received a covariate diet containing 16.9% CP [dry matter (DM) basis]. For the subsequent 12 wk, pens were randomly assigned to 1 of 4 treatments that contained 16.2, 14.4, 13.1, or 11.8% CP (DM basis). Diets were offered once daily and contained 32.5% corn silage, 32.5% alfalfa silage, 13.5% high-moisture corn, and 21.5% concentrate mix. A reduction in dietary CP was achieved by replacing soybean meal with soy hulls in the concentrate mix (DM basis). Dry matter intake, milk urea N (MUN; mg/dL), and the yield of milk urea N (g/d) decreased linearly with dietary CP. Compared with a 16.2% CP diet, a 14.4% CP diet did not alter milk yield throughout the study, but the 13.1 and 11.8% CP diets reduced milk yield after 4 and 1 wk, respectively. Furthermore, milk protein percentage was reduced for all dietary CP less than 16.2%, but this negative effect was temporary and disappeared after 7 wk for the 14.4% CP diet. In contrast, MUN adjusted to a new steady state within 1 wk for all dietary treatments. Modeling quadratic responses with a plateau led to predictions of no reduction in fat- and protein-corrected milk (32.6 kg/d) and yields of fat (1.31 kg/d), lactose (1.49 kg/d), and true protein (1.12 kg/d) until dietary CP decreased below 15.5, 15.3, 15.9, and 16.2%, respectively. In this study, MUN and the yield of MUN were highly correlated with N intake, milk protein yield, and fat- and protein-corrected milk. Surprisingly, N use efficiency (milk protein N/intake N) was not correlated with any variables related to N utilization and reached an apparent upper limit of approximately 30%. Although this observation may be associated with feeding diets deficient in metabolizable protein, late-lactation cows in this study adjusted to low dietary CP concentration better than anticipated as milk production was 2.6, 3.6, 6.4, and 8.0 kg/d higher than National Research Council (2001)-predicted metabolizable protein-allowable milk for dietary CP of 16.2, 14.4, 13.1, and 11.8%, respectively., (Copyright © 2017 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Our objective was to determine the effects of a tannin mixture extract on lactating cow performance, rumen fermentation, and N partitioning, and whether responses were affected by dietary crude protein (CP). The experiment was conducted as a split-plot with 24 Holstein cows (mean ± standard deviation; 669±55kg of body weight; 87±36 d in milk; 8 ruminally cannulated) randomly assigned to a diet of [dry matter (DM) basis] 15.3 or 16.6% CP (whole plot) and 0, 0.45, 0.90, or 1.80% of a tannin mixture in three 4×4 Latin squares within each level of CP (sub-plot). Tannin extract mixture was from quebracho and chestnut trees (2:1 ratio). Dietary CP level did not influence responses to tannin supplementation. A linear decrease in DM intake (25.5 to 23.4kg/d) was found, as well as a linear increase in milk/DM intake (1.62 to 1.75) and a trend for a linear decrease in fat-and-protein-corrected milk (38.4 to 37.1kg/d) with increasing levels of tannin supplementation. In addition, there was a negative linear effect for milk urea N (14.0 to 12.9mg/dL), milk protein yield (1.20 to 1.15kg), and concentration (2.87 to 2.83%). Furthermore, the change in milk protein concentration tended to be quadratic, and predicted maximum was 2.89% for a tannin mixture fed at 0.47% of dietary DM. Tannin supplementation reduced ruminal NH3-N (11.3 to 8.8mg/dL), total branched-chain volatile fatty acid concentration (2.97 to 2.47mol/100mol), DM, organic matter, CP, and neutral detergent fiber digestibility. Dietary tannin had no effect on intake N (587±63g/d), milk N (175±32g/d), or N utilization efficiency (29.7±4.4%). However, feeding tannin extracts linearly increased fecal N excretion (214 to 256g/d), but reduced urinary N (213 to 177g/d) and urinary urea N (141 to 116g/d) excretion. Decreasing dietary CP did not influence milk production, but increased N utilization efficiency (milk N/N intake; 0.27 to 0.33), and decreased milk urea N (15.4 to 11.8mg/dL), ruminal NH3-N (11.0 to 9.3mg/dL), apparent digestibility of DM (66.1 to 62.6%), organic matter (68.2 to 64.3%), and CP (62.9 to 55.9%), as well as urinary N excretion (168 vs. 232g/d). Results of this study indicated beneficial effects of 0.45% tannin extract in the diet on milk protein content. Increasing tannin extract levels in the diet lowered urinary N excretion, but had detrimental effects on DM intake, milk protein content, milk protein yield, and nutrient digestibility., (Copyright © 2016 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The objective was to study repeatability and sources of variation in feed conversion efficiency [FCE, milk kg/kg dry matter intake (DMI)] of lactating cows in mid to late lactation. Trials 1 and 2 used 16 cows (106 to 368 d in milk) grouped in 8 pairs of 1 high- and 1 low-FCE cow less than 16 d in milk apart. Trial 1 determined the repeatability of FCE during a 12-wk period. Trial 2 quantified the digestive and metabolic partitioning of energy and N with a 3-d total fecal and urine collection and measurement of CH4 and CO2 emission. Trial 3 studied selected ruminal methanogens in 2 pairs of cows fitted with rumen cannulas. Cows received a single diet including 28% corn silage, 27% alfalfa silage, 17% crude protein, and 28% neutral detergent fiber (dry matter basis). In trial 1, mean FCE remained repeatedly different and averaged 1.83 and 1.03 for high- and low-FCE cows, respectively. In trial 2, high-FCE cows consumed 21% more DMI, produced 98% more fat- and protein-corrected milk, excreted 42% less manure per kilogram of fat- and protein-corrected milk, but emitted the same daily amount of CH4 and CO2 compared with low-FCE cows. Percentage of gross energy intake lost in feces was higher (28.6 vs. 25.9%), but urinary (2.76 vs. 3.40%) and CH4 (5.23 vs. 6.99%) losses were lower in high- than low-FCE cows. Furthermore, high-FCE cows partitioned 15% more of gross energy intake toward net energy for maintenance, body gain, and lactation (37.5 vs. 32.6%) than low-FCE cows. Lower metabolic efficiency and greater heat loss in low-FCE cows might have been associated in part with greater energy demand for immune function related to subclinical mastitis, as somatic cell count was 3.8 fold greater in low- than high-FCE cows. As a percentage of N intake, high-FCE cows tended to have greater fecal N (32.4 vs. 30.3%) and had lower urinary N (32.2 vs. 41.7%) and greater milk N (30.3 vs. 19.1%) than low-FCE cows. In trial 3, Methanobrevibacter spp. strain AbM4 was less prevalent in ruminal content of high-FCE cows, which emitted less CH4 per unit of DMI and per unit of neutral detergent fiber digested than low-FCE cows. Thus lower digestive efficiency was more than compensated by greater metabolic efficiencies in high- compared with low-FCE cows. There was not a single factor, but rather a series of mechanisms involved in the observed differences in efficiency of energy utilization of the lactating cows in this study., (Copyright © 2015 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The objective of this study was to evaluate the effect of integrating dairy and bioenergy systems on land use, net energy intensity (NEI), and greenhouse gas (GHG) emissions. A reference dairy farm system representative of Wisconsin was compared with a system that produces dairy and bioenergy products. This integrated system investigates the effects at the farm level when the cow diet and manure management practices are varied. The diets evaluated were supplemented with varying amounts of dry distillers grains with solubles and soybean meal and were balanced with different types of forages. The manure-management scenarios included manure land application, which is the most common manure disposal method in Wisconsin, and manure anaerobic digestion (AD) to produce biogas. A partial life cycle assessment from cradle to farm gate was conducted, where the system boundaries were expanded to include the production of biofuels in the analysis and the environmental burdens between milk and bioenergy products were partitioned by system expansion. Milk was considered the primary product and the functional unit, with ethanol, biodiesel, and biogas considered co-products. The production of the co-products was scaled according to milk production to meet the dietary requirements of each selected dairy ration. Results indicated that land use was 1.6 m2, NEI was 3.86 MJ, and GHG emissions were 1.02 kg of CO2-equivalents per kilogram of fat- and protein-corrected milk (FPCM) for the reference system. Within the integrated dairy and bioenergy system, diet scenarios that maximize dry distillers grains with solubles and implement AD had the largest reduction of GHG emissions and NEI, but the greatest increase in land use compared with the reference system. Average land use ranged from 1.68 to 2.01 m2/kg of FPCM; NEI ranged from -5.62 to -0.73 MJ/kg of FPCM; and GHG emissions ranged from 0.63 to 0.77 kg of CO2-equivalents/kg of FPCM. The AD contributed 65% of the NEI and 77% of the GHG emission reductions., (Copyright © 2015 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

This study explored whether technology adoption and changes in management practices were associated with farm structure, household, and farmer characteristics and to identify processes that may foster productivity and sustainability of small-scale dairy farming in the central highlands of Mexico. Factor analysis of survey data from 44 smallholders identified three factors-related to farm size, farmer's engagement, and household structure-that explained 70 % of cumulative variance. The subsequent hierarchical cluster analysis yielded three clusters. Cluster 1 included the most senior farmers with fewest years of education but greatest years of experience. Cluster 2 included farmers who reported access to extension, cooperative services, and more management changes. Cluster 2 obtained 25 and 35 % more milk than farmers in clusters 1 and 3, respectively. Cluster 3 included the youngest farmers, with most years of education and greatest availability of family labor. Access to a network and membership in a community of peers appeared as important contributors to success. Smallholders gravitated towards easy to implement technologies that have immediate benefits. Nonusers of high investment technologies found them unaffordable because of cost, insufficient farm size, and lack of knowledge or reliable electricity. Multivariate analysis may be a useful tool in planning extension activities and organizing channels of communication to effectively target farmers with varying needs, constraints, and motivations for change and in identifying farmers who may exemplify models of change for others who manage farms that are structurally similar but performing at a lower level.

Two trials were conducted simultaneously to study the effects of varying alfalfa silage (AS) to corn silage (CS) ratio in diets formulated to avoid excess protein or starch on lactating dairy cow performance, digestibility, ruminal parameters, N balance, manure production and composition, and gaseous emissions [carbon dioxide (CO2), methane (CH4), and ammonia-N (NH3-N)]. In trial 1 all measurements, except gas emissions, were conducted on 8 rumen-cannulated cows in replicated 4×4 Latin squares. In trial 2, performance and emissions were measured on 16 cows randomly assigned to 1 of 4 air-flow controlled chambers in a 4×4 Latin square. Dietary treatments were fed as total mixed rations with forage-to-concentrate ratio of 55:45 [dietary dry matter (DM) basis] and AS:CS ratios of 20:80, 40:60, 60:40, and 80:20 (forage DM basis). Measurements were conducted the last 3d of each 21-d period. Treatments did not affect DM intake, DM digestibility, and milk/DM intake. However, responses were quadratic for fat-and-protein-corrected milk, fat, and protein production, which reached predicted maxima for AS:CS ratio of 50:50, 49:51, and 34:66, respectively. Nitrogen use efficiency (milk N/N intake) decreased from 31 to 24g/100g as AS:CS ratio increased from 20:80 to 80:20. Treatments did not alter NH3-N/milk-N but tended to have a quadratic effect on daily NH3-N emission. Treatments had a quadratic effect on daily CH4 emission, which was high compared with current literature; they influenced CH4 emission per unit of neutral detergent fiber (NDF) intake and tended to influence CO2/NDF intake. Ruminal acetate-to-propionate ratio and total-tract NDF digestibility increased linearly with increasing AS:CS ratio. In addition, as AS:CS ratio increased from 20:80 to 80:20, NDF digested increased linearly from 2.16 to 3.24kg/d, but CH4/digested NDF decreased linearly from 270 to 190g/kg. These 2 counterbalancing effects likely contributed to the observed quadratic response in daily CH4 emission, which may have been influenced also by increasing starch with increasing CS in the diet as reflected by the increased ruminal propionate molar proportion. Overall, production performances were greatest for the intermediate AS:CS ratios (40:60 and 60:40), but daily excretion of urine, manure, fecal N, urinary urea N, and urinary N decreased with increasing proportion of CS in the diet, whereas daily CH4 emission was reduced for the 2 extreme AS:CS ratios (20:80 and 80:20). However, the proportion of AS and CS in the diet did not affect CH4/fat-and-protein corrected milk., (Copyright © 2015 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Urinary urea N (UUN) is the principal nitrogen (N) source controlling emissions of ammonia (NH) and nitrous oxide (NO) from dairy manure. The objectives of this study were (i) to study the integrative nature of dietary crude protein (CP) management, secretion of milk urea N (MUN), excretion of UUN, and N emissions from dairy production systems; (ii) to evaluate how associative changes in dietary CP, MUN, and UUN affect atmospheric N emissions from dairy farms; and (iii) to discuss some of the challenges and opportunities to an expanded use of MUN to enhance dietary CP use and decrease UUN excretion and N emissions from dairy farms. Milk urea N records of 37,889 cows in 197 herds in Wisconsin revealed that approximately one half of tested cows were likely consuming dietary CP in excess of requirement. Farm simulations were used to quantify the effect of dietary CP on whole-farm N emissions. At a statewide average MUN of 12.5 mg dL, 48 to 87% of UUN was emitted as NH, with the lowest loss from pasture-based farms and the greatest loss from tie-stall farms. Each 1 mg dL decrease of MUN (range, 16-10 mg dL) provided an associated daily decrease in UUN of 16.6 g per cow, which decreased NH and NO emissions from manure by 7 to 12%. Although more site-specific information is required on herd MUN-UUN relationships and more a reliable interpretation of MUN assay results is needed, monitoring of MUN may be used to enhance dietary CP use and to reduce UUN excretion and N emissions from Wisconsin dairy farms., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

Sixteen 200-L barrels were used to determine the effects of dietary forage-to-concentrate (F:C) ratio on the rate of NH(3)-N, N(2)O, CH(4), and CO(2) emissions from dairy manure during a 77-d storage period. Manure was obtained from a companion study where cows were assigned to total mixed rations that included the following F:C ratio: 47:53, 54:46, 61:39, and 68:32 (diet dry matter basis) and housed in air-flow-controlled chambers constructed in a modified tiestall barn. On d 0 of this study, deposited manure and bedding from each emission chamber was thoroughly mixed, diluted with water (1.9 to 1 manure-to-water ratio) and loaded in barrels. In addition, on d 0, 7, 14, 28, 35, 49, 56, 63, 70, and 77 of storage, the rate of NH(3)-N, N(2)O, CH(4), and CO(2) emissions from each barrel were measured with a dynamic chamber and gas concentration measured with a photo-acoustic multi-gas monitor. Data were analyzed as a randomized complete block with 4 replications. Dietary F:C ratio had no effect on manure dry matter, total N and total ammoniacal-N (NH(3)-N + NH(4)(+)-N), or pH at the time of storage (mean ± SD: 10.6±0.6%, 3.0±0.2%, 93.1±18.1 mg/dL, and 7.8±0.5, respectively). No treatment differences were observed in the overall rate of manure NH(3)-N, N(2)O, CH(4), and CO(2) emissions (mean ± SD over the 77-d storage period; 117±25, 30±7, 299±62, and 15,396±753 mg/hr per m(2), respectively). The presence of straw bedding in manure promoted the formation of a surface crust that became air dried after about 1 mo of storage, and was associated with an altered pattern in NH(3)-N and N(2)O emissions in particular. Whereas NH(3)-N emission rate was highest on d 0 and gradually decreased until reaching negligible levels on d 35, N(2)O emission rate was almost zero the first 2 wk of storage, increased sharply to peak on d 35, and decreased subsequently. The emission rate of CH(4) and CO(2) peaked simultaneously on d 7, but decreased subsequently until the end of the storage period. In this study, C:N ratio of gaseous losses was 32:1, reflecting higher volatile C loss than volatile N loss during storage. On a CO(2)-equivalent basis, the most important source of non-CO(2) greenhouse gas emitted was CH(4) until formation of an air-dried crust, but N(2)O thereafter. Taken together, these results suggested that the formation of an air-dried crust resulting from the straw bedding present in the manure reduced drastically NH(3)-N, and CH(4) emissions, but was conducive of N(2)O production and emission., (Copyright © 2012 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Twelve 200-L barrels were used to determine the effects of N content and straw addition on changes in chemical composition and volatile losses measured by mass balance of dairy manure during a 136-d storage period. In addition, on d 0, 3, 6, 12, 28, 56, and 136, rate of NH₃-N emission was measured, and core samples were collected to characterize fermentation pattern. High N (3.06% N, HN) and low N (2.75% N, LN) manures were obtained from cows fed diets with 17.2 and 15.2% crude protein (dry matter basis), respectively. On d 0, manure scraped from a freestall barn floor was diluted with water to 10% dry matter and loaded in barrels with (+S) or without (-S) mixing 22g of chopped wheat straw per kilogram of undiluted manure. Data were analyzed as a randomized complete block with a 2×2 factorial arrangement of treatments and 3 replications. We observed no interaction between treatments for the reported measurements, but several day-of-storage by treatment interactions were found. Throughout storage, total NH₃-N (TAN, NH₃-N + NH₄⁺-N; 71.9 vs. 104.3 mg/dL), pH (6.40 vs. 6.74), and total volatile fatty acids (TVFA, starting on d 12) were lower for LN relative to HN manure. In the presence of straw, crust formation occurred between d 12 and 28, and pH became lower and TVFA became higher starting on d 56, compared with no straw. Treatments did not influence loss of organic matter, organic N, organic C, or N, which averaged 31, 29, 26, and 20%, respectively. However, neutral detergent fiber loss was 44% higher for +S relative to -S manure. Consistent reductions in the C:N ratio indicated proportionally higher volatile C loss than volatile N loss during storage. Overall rate of NH₃-N emission was 36% lower for LN than for HN manure. In the presence of straw, rate of NH₃-N emission did not differ until after crust formation, but was 67% lower on d 56 and 95% lower on d 136, when it was barely detectable, compared with manure with no straw. Manure pH was highly correlated with TVFA:TAN ratio (r=-0.78), and rate of NH₃-N emission was correlated with pH, TVFA:TAN, TVFA, and TAN (r=0.47, -0.44, -0.23, and 0.28, respectively). In this trial, both microbial fermentation and crust formation influenced NH₃-N emission rate and other measured responses, highlighting the importance of long-term sampling to evaluate treatment effects in manure storage studies., (Copyright © 2012 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The objective of the work was to identify local feeding strategies in small-scale dairy production systems during the rainy season in the highlands of Mexico, and to determine their effects on milk yields (MY), milk composition and economic viability. Twenty-two dairy farms were monitored by monthly visits, recording and sampling milk from between two and six cows in each farm, live-weight was also recorded. Samples from feeds used in that month were taken and feeds given to the dairy herd were weighed. Economic data was also recorded. Milk composition and milk urea nitrogen were determined, as well as chemical composition of feeds. Eighteen feedstuffs were identified, grouped in: HNH feeds-high in neutral detergent fibre (NDF) and in DM matter; HNL feeds-high in NDF but low in DM; HCh feeds-high in non-fibrous carbohydrates; and HCP feeds-high in crude protein. Four feeding strategies were identified: strategy 1 uses HND, HNL and HCP; strategy 2-HND, HNL, HCh and HCP; strategy 3 HNH and HCP; and strategy 4 HNL and HCP. Of participating farms, 73.4% followed strategy 1, 11.3% strategy 2, 11.3% strategy 4 and 3.8% strategy 3. There were no statistical differences (P > 0.05) between strategies for MY and milk composition, but there were differences (P < 0.05) for ration costs. Multiple regression analysis showed no significative (P > 0.05) model relating intake of feed groups and milk fat content, but milk protein and SNF contents were significantly explained by intake of HCP. When expressed as MY and milk components yield, milk fat yield was significantly explained by intake of all four feed groups, but milk protein and SNF yields were explained only by intake of HCP and LW. MUN excretion was explained also by HCP intake. All feeding strategies produced positive economic returns, on average generating the equivalent of 3.45 minimum wages of the area.

Excess crude protein (CP) in dairy cow diets is excreted mostly as urea nitrogen (N), which increases ammonia (NH) emissions from dairy farms and heightens human health and environmental concerns. Feeding less CP and more tannin to dairy cows may enhance feed N use and milk production, abate NH emissions, and conserve the fertilizer N value of manure. Lab-scale ventilated chambers were used to evaluate the impacts of CP and tannin feeding on slurry chemistry, NH emissions, and soil inorganic N levels after slurry application to a sandy loam soil and a silt loam soil. Slurry from lactating Holstein dairy cows (Bos taurus) fed two levels of dietary CP (low CP [LCP], 155 g kg; high CP [HCP], 168 g kg) each fed at four levels of dietary tannin extract, a mixture from red quebracho (Schinopsis lorentzii) and chestnut (Castanea sativa) trees (0 tannin [0T]; low tannin [LT], 4.5 g kg; medium tannin [MT], 9.0 g kg; and high tannin [HT], 18.0 g kg) were applied to soil-containing lab-scale chambers, and NH emissions were measured 1, 3, 6, 12, 24, 36, and 48 h after slurry application. Emissions from the HCP slurry were 1.53 to 2.57 times greater ( < 0.05) than from the LCP slurry. At trial's end (48 h), concentrations of inorganic N in soils were greater ( < 0.05) in HCP slurry-amended soils than in LCP slurry-amended soils. Emissions from HT slurry were 28 to 49% lower ( < 0.05) than emissions from 0T slurry, yet these differences did not affect soil inorganic N levels. Emissions from the sandy loam soil were 1.07 to 1.15 times greater ( < 0.05) than from silt loam soil, a result that decreased soil inorganic N in the sandy loam compared with the silt loam soil. Larger-scale and longer-term field trails are needed to ascertain the effectiveness of feeding tannin extracts to dairy cows in abating NH loss from land-applied slurry and the impact of tannin-containing slurry on soil N cycles., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

The purpose of this study was to compile and evaluate relationships between feed nitrogen (N) intake, milk urea N (MUN), urinary urea N (UUN), and ammonia (NH(3)) emissions from dairy farms to aid policy development. Regression relationships between MUN, UUN, and NH(3) emissions were compiled from studies conducted in Wisconsin, California, and the Netherlands. Relative reductions in NH(3) emissions were calculated as percentage decreases in NH(3) emissions associated with a baseline MUN level of 14 mg/dL (prevailing industry average). For 3 studies with cows in stanchion barns, relative NH(3) emission reductions of 10.3 to 28.2% were obtained when MUN declined from 14 to 10mg/dL. Similarly, analyses of 2 freestall studies provided relative NH(3) emission reductions of 10.5 to 33.7% when MUN levels declined from 14 to 10mg/dL. The relative reductions in NH(3) emissions from both stanchion and freestall barns can be associated directly with reductions in UUN excretion, which can be determined using MUN. The results of this study may help create new awareness, and perhaps eventual industry-based incentives, for management practices that enhance feed N use efficiency and reduce MUN, UUN, and NH(3) emissions from dairy farms., (Copyright © 2011 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Holstein cows housed in a modified tie-stall barn were used to determine the effect of feeding diets with different forage-to-concentrate ratios (F:C) on performance and emission of CH(4), CO(2) and manure NH(3)-N. Eight multiparous cows (means ± standard deviation): 620 ± 68 kg of body weight; 52 ± 34 d in milk and 8 primiparous cows (546 ± 38 kg of body weight; 93 ± 39 d in milk) were randomly assigned to 1 of 4 air-flow controlled chambers, constructed to fit 4 cows each. Chambers were assigned to dietary treatment sequences in a single 4 × 4 Latin square design. Dietary treatments, fed as 16.2% crude protein total mixed rations included the following F:C ratio: 47:53, 54:46, 61:39, and 68:32 [diet dry matter (DM) basis]. Forage consisted of alfalfa silage and corn silage in a 1:1 ratio. Cow performance and emission data were measured on the last 7 d and the last 4 d, respectively of each 21-d period. Air samples entering and exiting each chamber were analyzed with a photo-acoustic field gas monitor. In a companion study, fermentation pattern was studied in 8 rumen-cannulated cows. Increasing F:C ratio in the diet had no effect on DM intake (21.1 ± 1.5 kg/d), energy-corrected milk (ECM, 37.4 ± 2.2 kg/d), ECM/DM intake (1.81 ± 0.18), yield of milk fat, and manure excretion and composition; however, it increased milk fat content linearly by 7% and decreased linearly true protein, lactose, and solids-not-fat content (by 4, 1, and 2%, respectively) and yield (by 10, 6, and 6%, respectively), and milk N-to-N intake ratio. On average 93% of the N consumed by the cows in the chambers was accounted for as milk N, manure N, or emitted NH(3)-N. Increasing the F:C ratio also increased ruminal pH linearly and affected concentrations of butyrate and isovalerate quadratically. Increasing the F:C ratio from 47:53 to 68:32 increased CH(4) emission from 538 to 648 g/cow per day, but had no effect on manure NH(3)-N emission (14.1 ± 3.9 g/cow per day) and CO(2) emission (18,325 ± 2,241 g/cow per day). In this trial, CH(4) emission remained constant per unit of neutral detergent fiber intake (1g of CH(4) was emitted for every 10.3g of neutral detergent fiber consumed by the cow), but increased from 14.4 to 18.0 g/kg of ECM when the percentage of forage in the diet increased from 47 to 68%. Although the pattern of emission within a day was distinct for each gas, emissions were higher between morning feeding (0930 h) and afternoon milking (1600 h) than later in the day. Altering the level of forage within a practical range and rebalancing dietary crude protein with common feeds of the Midwest of the United States had no effects on manure NH(3)-N emission but altered CH(4) emission., (Copyright © 2011 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Feeding more tannin and less crude protein (CP) to dairy cows may have synergistic impacts on reducing NH emissions from dairy barns. Three trials using lab-scale ventilated chambers with concrete floors were conducted to determine the impacts on NH emission of tannin and CP feeding, tannin feeding on urease activity in feces, and tannin application directly to the barn floor. For Trial 1, mixtures of feces and urine from lactating Holstein dairy cows () fed four levels (g kg) of dietary tannin extract [a mixture from red quebracho () and chestnut () trees]: 0 tannin (0T), 4.5 (low tannin [LT]), 9.0 (medium tannin [MT]), and 18.0 (high tannin [HT]); each fed at two levels (g kg) of dietary CP: 155 low CP (LCP) and 168 high CP (HCP) were applied to chambers. For Trial 2, urea solution was added to feces obtained from cows fed 0T, MT, and HT at HCP. For Trial 3, tannin amounts equivalent to those fed at 0T, MT, and HT were applied directly to feces-urine mixtures from 0T-HCP. For all trials, NH emissions were measured 1, 3, 6, 12, 24, 36, and 48 h after treatment application. For Trial 1, reductions in NH emission due to tannin feeding were greatest when fed at LCP: The LCP-LT and LCP-HT treatments emitted 30.6% less NH than LCP-0T, and the HCP-LT and HCP-HT treatments emitted 16.3% less NH than HCP-0T. For Trial 2, feeding tannin decreased urease activity in feces, resulting in an 11.5% reduction in cumulative NH loss. For Trial 3, the application of tannin directly to simulated barn floors also apparently decreased urease activity, resulting in an average reduction in cumulative NH emissions of 19.0%. Larger-scale trails are required to ascertain the effectiveness of tannin extracts in abating NH loss from dairy barn floors., (American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)

The main objective of this experiment was to monitor the impact of barn side and dietary crude protein (CP) on production performance, manure production and composition, and ammonia nitrogen (N) emission from a lactating dairy herd housed in a free-stall barn and managed under farm-like conditions throughout a number of months in each season of the year. The 78-cow lactating herd of the University of Wisconsin-Platteville (USA) was halved and each group was allocated to either the north or south side of the barn and either a recommended (REC) diet with 16.7 ± 1.3% CP dry matter basis (DM) or an excess (EXC) CP diet containing 1.5 units of CP above the REC diet (18.2 ± 1.5%). In 7 months between February 2004 and January 2005, total manure collection was conducted by manual scraping of the alleys and ammonia-N emission was calculated as intake N + bedding N - milk N - scraped manure N. Side of the barn (northern v. southern exposure) did not influence measurements and there was no effect of dietary CP on dry matter intake (DMI), milk, milk fat, and milk protein production, but a lower manure N concentration was observed for the group of cows fed the REC diet compared with the EXC diet (3.43% v. 3.66% of DM). Nitrogen intake was 63 g/day lower (643 v. 706 g/day), milk N was unaffected (157 g/day), manure N was 32 g/day lower (391 v. 423 g/day), and ammonia-N emission was 34 g/day lower (93 v. 127 g/day) for the group consuming the REC diet compared with the group consuming the EXC diet. There were larger variations in measured responses among months of the year than between level of dietary CP. Wet and dry manure excretions tended to be higher, but manure pH was reduced when corn silage became unavailable and the diet included additional corn grain and alfalfa silage as the only forage source. Prediction of manure N excretion for a group of cow determined as N intake - N milk was 9% higher than current prediction equations of the American Society of Agricultural Engineers. Ammonia-N loss averaged 110 g/day per lactating cow, but ranged from 64 g/day to 178 g/day with no clear seasonal pattern. There was no clear association between barn temperature, manure temperature or manure pH and ammonia-N emission; however, intake N explained 61% of the variation in ammonia-N emission.

In this study, animal or dairy sciences faculty from doctoral/research universities were surveyed to clarify teaching performance expectations for the purpose of promotion and tenure of assistant professors. A survey tool including 15 evaluation criteria was available online and at the registration desk of the 2005 Joint Annual Meeting of the American Dairy Science Association and the American Society of Animal Science. The analyzed data set included 47 faculty (41 tenured and 6 tenure-track) with a substantial teaching responsibility from 27 different departments in 25 states. Four criteria were perceived as currently overemphasized: student evaluation of the instructor, student evaluation of the course, authoring peer-reviewed publications, and authoring an undergraduate textbook or book chapter. Nevertheless, more than 50% of respondents reported that these criteria should be used. One criterion emerged as being currently underemphasized: documentation of personal assessment of one's own teaching by preparing a portfolio. The lack of consensus for the remaining 10 items may have reflected substantial differences in institutional practices. The significance of overemphasis or underemphasis of certain criteria varied substantially depending on the respondent's perceived institutional mission. When asked about recognition within their department, 68% of respondents indicated that efforts in teaching improvement were properly rewarded. Respondents doubted the meaningfulness and appropriateness of student ratings tools as currently used. Results also suggested that animal and dairy science faculty placed a higher value on criteria recognizing excellence in teaching based on intradepartmental recognition (e.g., interactions with close-up peers and students) rather than recognition within a broader community of scholars as evidenced by authorship or success in generating funding for teaching. Proposed improvements in the evaluation of teaching for promotion and tenure include 1) providing tenure-track faculty with written guidelines at the time of hiring; 2) ensuring that student ratings tools are reliable and valid; 3) carefully mentoring new faculty within the departmental and institutional culture; and 4) encouraging self-reflection and documentation of attempts to address pedagogical issues in one's own teaching. Educational leaders in doctoral/research universities should promote changes to enhance teaching performance of future faculty graduating from their institutions., (Copyright (c) 2010 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

This 3-yr classroom research project studied students' perception of the learning environment when class time was reserved primarily for discussion of preassigned reading material as an alternative to a lecture in ruminant nutrition. A student-assessment-of-learning-gain instrument with 46 items was administered anonymously as a survey 3-wk into the semester and as a course evaluation at the end of the semester. Scores, collected on a scale of 1 to 10, were analyzed to determine differences between survey and evaluation, the variation due to student cohort (years 2003, 2004, and 2005), and student standing (undergraduate or graduate) for 5 selected items: item 1 = My level of interest/ curiosity for nutrition is; item 17 = The reading assignments help me learn; item 18 = The in-class discussions help me learn; item 24 = I would prefer the professor lecture; item 38 = I am learning a lot in this class. Although students indicated a preference to using class time for discussion rather than lecture, the degree of consensus was low, as 10% of scores indicated a strong desire for lecture, whereas another 10% indicated strong opposition to lecture. Reading assignments and in-class discussions contributed positively to the perception of learning and both were correlated positively with level of interest in the topic. In the evaluation, the desire for lecture was correlated negatively with level of interest in the topic and the self-assessed level of learning. Students reported a greater interest in the topic at the end of the semester than at wk 3; however, the self-reported learning gains from discussion-related activities varied with student cohort. Graduate students reported a higher interest, more learning from discussion-related activities, and less desire for lecture than undergraduates. Although graduate students were more impervious to the discussion format, undergraduates perceived more learning if the discussion was student-centered (i.e., focused on their questions and answers), rather than subject-centered (i.e., focused on the paper content).

Urine excretion is a substantial factor in the amount of manure that needs to be managed, and urinary N can contribute to ammonia volatilization. Development and validation of prediction equations focusing on dietary factors to decrease urine and urinary nutrient excretion will provide information for managing urine and feces separately or for other future technologies. The objective of this study was to develop equations for prediction of urine excretion and excretion of urinary N, Na, and K and to evaluate both new and previously published prediction equations for estimation of urine and urinary nutrient excretion from lactating dairy cows. Data sets from metabolism studies conducted at Washington State University were compiled and evaluated for excretion of minerals. Urine excretion averaged 24.1 kg/d and urinary nitrogen excretion ranged from 63 to 499 g/d in the calibration data set. Regression equations were developed to predict urine excretion, urinary N excretion, and urinary Na and K excretion. Predictors used in the regression equations included milk yield, body weight, dietary crude protein percentage, milk urea nitrogen, and nutrient intakes. Previously published prediction equations were evaluated using data sets from Washington State University and the University of Wisconsin. Mean and linear biases were evaluated by determining the regression of residuals on predicted values. Evaluation and validation of prediction equations are important to develop equations that will more accurately estimate urine and urinary nitrogen excretion from lactating dairy cows.

In this study, 400,729 Dairy Herd Improvement (DHI) records collected on 77,178 cows in 692 Midwest herds over 29 mo (January 1999 to May 2001) were used to analyze milk urea nitrogen (MUN) as collected the day of the test in 6 breeds. Records of Holsteins, Jerseys, and Brown Swiss were subjected to stepwise backward elimination analysis with a model including parity (primiparous vs. multiparous cows), sample type (morning vs. evening), milking frequency (2x vs. 3x [Holstein only]), season (winter, spring, summer, and fall), yield of fat-corrected milk (FCM) classified into 1 of 3 FCM categories (FCMc) and all possible higher-order interactions. Results indicated that FCMc contributed to test-day MUN variation in multiparous, but not primiparous, Holsteins. Sample type and season were significant in both parity groups; milking frequency was not significant, but milking frequency x season and milking frequency x FCMc were significant in both parity groups. The nature of these interactions differed for each parity group. For Jersey and Brown Swiss data analyzed by sample type separately, parity was not significant but tended to interact with FCMc, whereas season, FCMc, and season x FCMc were generally significant. Mean test-day MUN was 12.7, 14.6, and 14.4 mg/dL, with 24, 45, and 42% of records above 14.5 mg/dL in Holsteins, Jerseys, and Brown Swiss in single-breed herds, respectively. In Holsteins, MUN peaked at 7 to 10 d in milk (DIM), declined until 28 to 35 DIM, and rose again thereafter. In primiparous Holsteins, MUN did not change with FCM

Eight Holstein cows (4 primiparous and 4 multiparous) were used in a replicated 4 x 4 Latin square design to determine milk production response and N balance when diets had no NRC-predicted excess of rumen-undegradable protein (RUP) or rumen-degradable protein (RDP), 10% RUP excess, 10% RDP excess, or 10% excess of both RUP and RDP. Diets were fed as a total mixed ration with (dry matter basis) 25% alfalfa silage, 25% corn silage, 19 to 21% corn grain, and varying proportions of solvent soybean meal and expeller soybean meal as primary sources of supplemental RDP and RUP, respectively. Milk yield and dry matter intake (DMI) were recorded daily, and total collection of feces and urine was completed in the last 3 d of each 21-d period. Dietary crude protein averaged 17.5 and 18.5% for the recommended and excess RDP diets, respectively, and 17.3 and 18.4% for the recommended and excess RUP diets, respectively. When cows were fed excess RUP diets in the form of expeller soybean meal, DMI and milk production increased, but the opposite was true when the diets contained excess RDP in the form of solvent soybean meal. Milk composition was not affected by RDP, RUP, or by parity, and there were no parity x RDP interactions for any of the measurements. However, apparent digestibility of neutral detergent fiber, dry matter, and N increased in multiparous cows but not in primiparous cows because of excess RUP. The increase in the yield of milk N with excess RUP was not influenced by parity, but multiparous cows retained more of the additional N apparently absorbed, whereas primiparous cows excreted the additional apparently absorbed N in the urine. Overall, the difference in urinary N due to parity (70 g/d) was about 4 times greater than the impact of dietary treatments (17 g/d). Our results suggest that multiparous cows have either a much larger urea pool or a greater demand to restore body protein mobilized earlier in lactation compared with primiparous cows. Reduction in urinary N excretion in commercial dairy herds could be obtained by separately balancing rations for first and later lactations.

This study was designed to evaluate lactational responses of cows fed corn silage (CS) or alfalfa silage (AS) as primary forage source when the diet was balanced for recommended (RP) or excessive (HP) amounts of rumen degradable protein (RDP) and undegradable protein (RUP) according to the recommendations of the National Research Council (NRC). A second objective was to evaluate different sources of variations in milk urea N (MUN). The total mixed rations included 55% forage on a dry matter (DM) basis as either 14% CS and 41% AS or 14% AS and 41% CS. Diets were offered to 48 multiparous Holstein cows (body weight = 652 kg) that were assigned randomly to treatments arranged as a 2 x 2 factorial in 12 complete blocks based on calving date. Data collected during wk 4 to 12 of lactation were adjusted to those obtained from a pretreatment diet fed during wk 1 to 3. Crude protein (CP) averaged 16.5, 18.0, 16.2, and 17.1% of DM in the AS-RP; AS-HP; CS-RP; and CS-HP diets, respectively. Overall DM intake (DMI) was 1.5 kg/d lower than predicted by NRC (24.6 vs. 26.1 kg/d), but 3.5% fat-corrected milk (FCM) was higher than expected (46.1 vs. 45.0 kg/d). The responses to a reduction in dietary protein were independent of primary forage source, except for milk true protein (TP) percentage. Primary forage source did not influence DMI, 3.5% FCM, TP yield, or MUN. However, compared with the AS-based diets, cows fed CS-based diets produced more milk (49.0 vs. 46.4 kg/d), less fat (3.07% vs. 3.54% and 1500 vs. 1651 g/d), and tended to gain more body weight. There were no benefits to feeding diets above NRC protein recommendations, regardless of forage source. Reducing CP from 17.5 to 16.4% of diet DM did not alter milk yield (47.7 kg/d) or milk TP yield (1293 g/d), but lowered N intake by 65 g/d (700 vs. 635 g/d) and lowered MUN by 1 unit (12.7 vs. 11.7 mg/dL). A positive correlation between MUN and production efficiency (3.5% FCM/DMI) on wk 3 of lactation suggested that body protein mobilization might impact MUN in early lactation. The correlation between MUN and DMI tended to be negative in wk 3, but was positive in wk 6 to 12 of lactation. The same was true for the correlation between MUN and somatic cell score. Regression analysis of the postpeak lactation data of this study indicated that the expected MUN was essentially 12 mg/dL when NRC-predicted RDP and RUP balances were 0 g/d, with a linear deviation of 0.1 and 0.03 mg/dL per 10 g of change in RDP and RUP balance, respectively.

This N balance study was completed with 48 multiparous Holstein cows (body weight [BW] = 653 kg; days in milk = 89) blocked by calving date and assigned to a 2 x 2 factorial arrangement of dietary treatments. The total mixed ration included alfalfa silage (AS) or corn silage (CS) as the primary forage source (41 and 14% vs. 14 and 41% of diet dry matter (DM), respectively) and were formulated for recommended (RP) or excessive (HP) amounts of rumen degradable protein (RDP) and rumen undegradable protein (RUP) according to the guidelines of the National Research Council (NRC). Crude protein (CP) averaged 16.5, 18.0, 16.4, and 17.3% for the AS-RP; AS-HP; CS-RP; and CS-HP diet, respectively (DM basis). Regardless of primary forage source, the reduction in dietary CP to the NRC guidelines tended to improve milk yield (43.4 vs. 41.0 kg/d) but did not alter 3.5% fat-corrected milk (37.0 kg/d) or milk true protein yield (1167 g/d). In this trial, cows fed the CS-based diets consumed less DM than those fed the AS-based diets in part because of rumen acidosis. The adverse effect of low rumen pH was accompanied by an increase in urinary N (UN) as a percentage of N intake, but did not alter milk yield. Notwithstanding partial confounding, fecal N (FN) was 49 g/d lower (213 vs. 164 g/d), UN was unchanged (229 g/d), but milk N tended to be higher (194 vs. 206 g/d) when cows were fed the CS-based diets compared with AS-based diets. Compared with the HP diets, cows fed the RP diets had similar FN (189 g/d) and milk N (200 g/d), but UN and urine urea N were reduced by 41 g/d (249 vs. 208 g/d) and 40 g/d (210 vs. 171 g/d), respectively. Fecal N concentration was higher for CS-based diets, but urinary N concentration was higher for AS-based diets. The reduction in dietary CP did not influence these concentrations but lowered urine volume. The metabolic relationships between energy and protein in determining the fate of excess dietary N (primarily in the form of excess RUP in this trial) was illustrated by a 17% increase in the UN to FN ratio for cows fed AS-HP compared with the AS-RP diet and a 42% increase in the UN to FN ratio for CS-HP compared with CS-RP diet, when cows' energy status was compromised because of rumen acidosis. In this trial, UN ranged from 150 to 320 g/d, and was best predicted as UN (g/d) = 0.0283 x BW (kg) x milk urea N (mg/dL). The NRC protein guidelines should not be exceeded to avoid unnecessary losses of manure N and, in particular, urine urea N.

Mixed ruminal bacteria were cultured with glucose, cellulose or no carbohydrate, and ammonium bicarbonate or casein hydrolysate. Changes in amounts of bacterial ammonia and non-ammonia N were measured. Ratios of N isotopes expressed as delta 15N (delta 15N) were measured by isotope ratio mass spectrometry. When bacteria were cultured with glucose and ammonium bicarbonate, bacterial delta 15N decreased from .9 to -5.8/1000 and residual ammonia delta 15N increased from -1.4 to 12.7/1000. Fractionation of N isotope occurred during ammonia incorporation because the difference between delta 15N of ammonia and delta 15N of bacteria (delta 15N) was 18.8/1000 (P < .01). However, when casein hydrolysate was the N source, delta 15N between non-ammonia and bacteria averaged only 1.3/1000 (P > .1), indicating no fractionation of N isotopes occurred during utilization of amino acids. The amount of bacterial N was highest at 24 h of incubation when cellulose was the carbohydrate source. At that time, delta 15N between ammonia and bacteria was 8.9/1000 when ammonia was the N source, but delta 15N between non-ammonia and bacteria was 1.7/1000 when casein hydrolysate was the N source. Bacterial N decreased after 24 h when cellulose was the source of carbohydrate. Results indicate that fractionation of N isotopes occurred during ammonia incorporation, but not during incorporation of N from amino acids, deamination, and release of ammonia. Fractionation of N isotopes during incorporation of ammonia N may be used as a marker to study N metabolism by ruminal bacteria.

Lactational responses to protein supplementation of diets containing 60% of DM as alfalfa silage were evaluated. Sixty muliparous Holstein cows were fed a covariant diet for the first 3 wk postpartum, blocked by calving date, and randomly assigned for 14 wk to one of six isonitrogenous (19.4% CP) diets. Diets were formulated with soybean meal, a blend of animal by-products, or both, and contained 5.0, 5.6, 5.6, 6.2, 6.1, and 6.8% ruminally undegradable protein (DM basis). Percentage of ruminally undegradable protein or source of supplemental protein did not affect 3.5% FCM (39.4 kg/d), milk fat yield (1.38 kg/d), milk protein percentage (2.83%), milk urea (7.66 mM), or plasma urea (8.91 mM). However, cows fed diets supplemented with soybean meal had higher DMI (26.2 vs. 24.7 kg/d), milk yields (40.4 vs. 39.1 kg/d), and milk protein (1.15 vs. 1.09 kg/d) yields, but lower milk fat concentration (3.42 vs. 3.53%) and body condition score (2.85 vs. 2.93) than cows fed diets containing a blend of animal by-products. The lack of response to ruminally undegradable protein was partially caused by higher than predicted DMI (5 to 15% above NRC predictions); all diets provided at least 1.3 kg of ruminally undegradable protein, and there was no beneficial effect from ruminally undegradable protein intake increases to 1.6 kg/d.

Kinetics of hydration of ground hay and silage particles (2-mm screen), determined by a pycnometric technique, was best described by a two- and one-pool exponential model, respectively. Fractional rates of hydration of the large pool, detected in hay particles only, and of the small pool present in both hay and silage particles averaged .135 and .021 min-1, respectively. When hydration was complete, liquid associated with particles averaged 1.16, 1.90, and .83 g/g of insoluble DM for bromegrass hay, alfalfa hay, and alfalfa silage, respectively. Functional specific gravity, which accounts for the effect of associated gas volume, averaged 1.54, 1.46, and 1.54, but unit specific gravity, calculated to include the effect of gases and liquid of hydration, averaged 1.22, 1.14, and 1.26 for bromegrass hay, alfalfa hay, and alfalfa silage, respectively. Preservation of forage as silage not only lowered gas volume, but also reduced water-holding capacity, both of which contribute to greater unit specific gravity and faster rate of escape from the rumen. In addition, estimates of unit specific gravity of approximately 1.2 indicate that even in the absence of associated gas, hydrated forage particles would tend to escape the rumen at a slower rate than that achieved by more dense particles.

Two experiments were designed to determine the effect of gas production during in vitro digestion on functional specific gravity (FSG) of forage particles. In Exp. 1, FSG of ground alfalfa hay decreased from 1.123 to 1.049 between 3 and 9 h of incubation and increased thereafter to reach a plateau at 1.309 after 30 h of incubation. Gas production peaked at 6 h, but gas associated with particles increased until 9 h of incubation. Gas associated with solid residue was correlated to gas production (r = -.67) but also was influenced by gas holding capacity and rate of escape from the particles. In Exp. 2, measurements were performed on ground alfalfa hay, alfalfa silage, and bromegrass hay containing 42.6, 35, and 66.4% NDF, respectively. Gas production seemed to be related to the amount of readily available substrate. Although at 9 h of incubation more gas was produced by alfalfa silage (.235 mL.min-1.g of DM-1) than by bromegrass hay and alfalfa hay (.087 and .187 mL.min-1.g of DM-1, respectively), gas associated with particles was greater for alfalfa hay (.416 mL/g of DM) than for bromegrass hay and alfalfa silage (.256 and .281 mL/g of DM, respectively). The increase in FSG was more rapid for alfalfa silage than for the hays. After 27 h of digestion, gas associated with particles (milliliters per gram of DM) and FSG were .164, 1.226; .147, 1.235; and .001, 1.467 for bromegrass hay, alfalfa hay, and alfalfa silage, respectively. Gas produced during fermentation delayed the increase in specific gravity of forage particles.(ABSTRACT TRUNCATED AT 250 WORDS)