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The objective of the current work was to parameterize the digestive elements of the model of Hill et al. (2008) using data collected from animals that were ruminally, duodenally, and ileally cannulated, thereby providing a better understanding of the digestion and metabolism of P fractions in growing and lactating cattle. The model of Hill et al. (2008) was fitted and evaluated for adequacy using the data from 6 animal studies. We hypothesized that sufficient data would be available to estimate P digestion and metabolism parameters and that these parameters would be sufficient to derive P bioavailabilities of a range of feed ingredients. Inputs to the model were dry matter intake; total feed P concentration (fPtFd); phytate (Pp), organic (Po), and inorganic (Pi) P as fractions of total P (fPpPt, fPoPt, fPiPt); microbial growth; amount of Pi and Pp infused into the omasum or ileum; milk yield; and BW. The available data were sufficient to derive all model parameters of interest. The final model predicted that given 75 g/d of total P input, the total-tract digestibility of P was 40.8%, Pp digestibility in the rumen was 92.4%, and in the total-tract was 94.7%. Blood P recycling to the rumen was a major source of Pi flow into the small intestine, and the primary route of excretion. A large proportion of Pi flowing to the small intestine was absorbed; however, additional Pi was absorbed from the large intestine (3.15%). Absorption of Pi from the small intestine was regulated, and given the large flux of salivary P recycling, the effective fractional small intestine absorption of available P derived from the diet was 41.6% at requirements. Milk synthesis used 16% of total absorbed P, and less than 1% was excreted in urine. The resulting model could be used to derive P bioavailabilities of commonly used feedstuffs in cattle production. [ABSTRACT FROM AUTHOR]

Characterizing phosphates in animal fecal and manure samples is of interest to environmental-monitoring research efforts. Acid extraction removes relatively mobile phosphates from samples, offering a better indicator of the mobility of phosphates in environment, but acidic extracts impose challenges to the solution phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy, which is commonly used for analyzing phosphates in environmental samples. Acid-extractable metals precipitate phosphates in the alkaline condition under which solution31P NMR experiment runs, blurring the spectrum for adequate analysis. We found that neutralizing acid extracts with 0.5 M sodium hydroxide (NaOH) plus 50 mM ethylenediaminetetraacetic acid (EDTA) before freeze drying eliminated the chemical interferences otherwise observed. The resulting31P NMR spectra can be used to quantify acid-soluble phytate and other phosphates in animal fecal and manure samples. The improvement in detection will support efforts to investigate the mobility of phosphates in feces and manures used as land amendments. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the effect of ferrous lactate infusion on postruminal P absorption in lactating dairy cows. Four ruminally cannulated lactating cows were used in a 4 x 4 Latin square design with 14 d per period. Cows were fed a basal diet containing 0.39% P, providing 100% of the calculated P requirement. On d 8 to 14 of each period, each cow was infused with 0, 200, 500, or 1,250 mg of Fe/d in the form of ferrous lactate solution (ferrous lactate in 1 L of double-distilled water) into the abomasum. Infusate was formulated to approximate 0, 2, 5, or 12.5 mg of Fe/L in drinking water with 100 L of water intake/d. Total fecal collection was conducted in the last 4 d of each period to measure nutrient digestion and excretion. Dry matter intake, milk yield, and milk composition were not affected by treatment. Digestibility of DM, NDF, and nitrogen decreased linearly with increasing ferrous lactate infusion. Infusion of ferrous lactate did not affect intake and digestibility of total P, inorganic P, or phytate P. In lactating cows, P absorption was not negatively influenced by abomasally infused ferrous lactate up to 1,250 mg of Fe/d. [ABSTRACT FROM AUTHOR]

Accumulation of estrogens in the environment is of concern because they disrupt the endocrine system of sensitive species. Livestock manure contains significant estrogens. We evaluated rentoval of 17β-estradiol (E2) and total estrogenicity (E2-eq) from dairy manure in pilot-scale reactor systems designed to remove ammonia or to generate methane: two were aerated (60% and 100% aeration), one was an anaerobic digester, and one was a nitrifying reactor receiving anaerobically digested manure. In all reactors, the influent contained more E2 and E2-eq than the effluent. Orthogonal contrasts were conducted to compare efficiency and rate of estrogen removal between reactors. The most consistent improvement in estrogen removal was associated with aeration and ammonia oxidation; reactors with varying levels of aeration and with high ammonia removal efficiencies removed estrogens faster and to a greater extent than those without. Anaerobic digestion pretreatment did not correlate with increased extent of estrogen removal in a downstream, fully aerated nitrifying reactor, but it did increase the rate of estrogen removal in the downstream reactor. Additional experiments evaluated a reactor designed to achieve low dissolved oxygen (DO) nitrification/denitrification, and one performing enhanced biological phosphorus (P) removal. While differing feed sources in the two sets of experiments prevent direct comparison, low DO denitrification achieved similar or greater removal of E2 and E2-equivalents as compared to fully aerated systems. Manure treatments designed to achieve nutrient removal or to generate methane have significant potential to reduce estrogen loading from dairy farms. [ABSTRACT FROM AUTHOR]

The United States Environmental Protection Agency has identified estrogens from animal feeding operations as a major environmental concern, but few data are available to quantify the excretion of estrogenic compounds by dairy cattle. The objectives of this study were to quantify variation in estrogenic activity in feces and urine due to increased dietary inclusion of phytoestrogens. Ten Holstein heifers were assigned to 2 groups balanced for age and days pregnant; groups were randomly assigned to treatment sequence in a 2-period crossover design. Dietary treatments consisted of grass hay or red clover hay, and necessary supplements. Total collection allowed for sampling of feed refusals, feces, and urine during the last 4 d of each period. Feces and urine samples were pooled by heifer and period, and base extracts were analyzed for estrogenic activity (estrogen equivalents) using the yeast estrogen screen bioassay. Feces and urine samples collected from 5 heifers were extracted and analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) to quantify excretion of 7 phytoestrogenic compounds. Excretion of 17-β estradiol equivalents in urine was higher and tended to be higher in feces for heifers fed red clover hay (84.4 and 120.2 mg/d for feces and urine, respectively) compared with those fed grass hay (57.4 and 35.6 mg/d). Analysis by LC-MS/MS indicated greater fecal excretion of equol, genistein, daidzein, coumestrol, and formononetin by heifers fed red clover hay (1634, 29.9, 96.3, 27.8, and 163 mg/d, respectively) than heifers fed grass hay (340, 3.0, 46.2, 8.8, and 18.3 mg/d, respectively). Diet had no effect on fecal biochanin A or 2-carbethoxy-5, 7-dihydroxy-4'-methoxyisoflavone. Four phytoestrogens were detected in urine (2-carbethoxy-5, 7-dihydroxy-4'-methoxyisoflavone, daidzein, equol, and formononetin) and their excretion was not affected by diet. Identifying sources of variation in estrogenic activity of manure will aid in the development of practices to reduce environmental estrogen accumulation. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate feces, urine, and N excretion by Jersey and Holstein cows. Sixteen multiparous cows (n = 8 per breed) were fed 2 experimental rations at calving in a switchback experimental design. Diets were 50% forage and based on corn meal (control) or whole cottonseed. Half the cows in each breed started on the control diet and half started on the whole cottonseed diet. Cows were switched to the other diet at 60 d in milk and switched back to their original diet at 165 d in milk. Pairs of cows were moved into open-circuit respiration chambers on d 49, 154, and 271 of lactation for 7-d measurement periods. While in the chambers, total collection of feed refusals, milk, recovered hair, feces, and urine was conducted. No effect of the interaction of diet and breed was observed for measures of nutrient digestibility and manure excretion. Total daily manure excretion was lower in Jersey cows than in Holstein cows, with reductions generally proportional to changes in feed intake. Jersey cows consumed 29% less feed and excreted 33% less wet feces and 28% less urine than Holstein cows. Intake, fecal, and urinary N were reduced by 29, 33, and 24%, respectively, in Jersey cows compared with Holstein cows. Equations from American Society of Agricultural and Biological Engineers underpredicted observed values for all manure measures evaluated (urine, manure solids, N, wet manure), and breed bias was observed in equations predicting excretion of urine, N, and wet manure. Although these equations include animal and dietary factors, intercepts of regression of observed values on predicted values differed between Holsteins and Jerseys for those 3 measures. No breed bias was observed in the prediction of manure solids excretion, however, making that equation equally appropriate for Jerseys and Holsteins. The effect of breed on manure and nutrient excretion has significant nutrient management implications. [ABSTRACT FROM AUTHOR]

Six Holstein heifers (body weight = 535-625 kg) fed a total mixed ration containing either high protein (13.4%) or low protein (9.0%) were used to evaluate the effect of 3 urine collection methods (chilled, acidified before collection, or acidified after 6 h of collection) on urinary N preservation. In a 2-period crossover design, 16-d diet adjustment stages preceded five 24-h collections. Urinary catheters were inserted 1 d before the collection periods. Urine collection tubes were configured to split urine to 3 collection containers: 1 acidified with 6 N HCl before collection at a rate calculated to reduce pH to below 2, 1 acidified every 6 h during collection to pH below 2, and 1 located in a large cooler of ice. Collection method did not affect urinary concentration of N or urine urea-N (9.2 ± 0.9 g/L and 6.58 ± 0.9 g/L, respectively) or urinary excretion of N or urea-N (82 ± 3.8 g/d and 59.5 ± 3.8 g/d, respectively). These 3 collection methods are equally effective in preserving N during urine collection, but the "chilled immediately" approach may be useful for studies focused on ammonia emission. Urinary and fecal N excretion were significantly different across collection days; fecal N was more highly variable than urinary N. Intake and apparent N digestibility decreased during the collection week, and excretion of urinary and fecal N increased, particularly on d 5. (Stable rectal temperatures suggested no urinary infections.) Improvements in total collection methodology will support continued progress in the understanding of livestock N utilization and post-excretion changes in manure N. [ABSTRACT FROM AUTHOR]

Calcium and P balance and mobilization from bone were evaluated through 20 wk of lactation to determine the timing and extent of net resorption of bone mineral and mineral balance in lactating dairy cows. Eighteen Holstein cows were blocked by parity and calving date and randomly assigned to 1 of 3 dietary treatments: high (1.03%, HI), medium (0.78%, MED), or low (0.52%, LOW) dietary Ca. Dietary P was 0.34% in all diets. Cows consumed treatment diets from calving to 140 DIM. Total collection of milk, urine, and feces was conducted 2 wk before expected calving and in wk 2, 5, 8, 11, and 20 of lactation. Blood samples were collected at 14 and 10 d before expected calving and 0, 1, 3, 5, 10, 14, 21, 28, 35, 56, 70, 84, 98, and 140 d after calving. Blood samples were analyzed for Ca, P, and parathyroid hormone concentration. Serum concentrations of osteocalcin (OC), a marker of bone formation, and deoxypyridinoline (DPD), a marker of bone resorption, were measured to assess bone mobilization. Rib bone biopsies were conducted within 10 d postcalving and during wk 11 and 20 of lactation. Dietary Ca concentration affected Ca balance, with cows consuming the HI Ca diet in positive Ca balance for all weeks with the exception of wk 11. Interestingly, all cows across all treatments had a negative Ca balance at wk 11, possibly the result of timed estrous synchronization that occurred during wk 11. At wk 20, Ca balances were 61.2, 29.9, and 8.1 g/d for the HI, MED, and LOW diets, respectively. Phosphorus balances across all treatments and weeks were negative. Bone Ca content on a fat-free ash weight basis was least in cows consuming the MED diet, but bone P was not different. Serum Ca and P were not affected by treatment. Dietary Ca concentration did not affect P balance in the weeks examined, but there was a clear effect of parity on balance, markers of bone metabolism, and bone P. Primiparous cows had greater serum OC and DPD concentrations than multiparous cows. Regardless of dietary treatment, serum OC concentration peaked around d 35 of lactation. Simultaneously, DPD concentration began to decrease, which may indicate a switch from net bone resorption to formation after d 35. However, this was not reflected in balance measures. This information may help refine dietary mineral recommendations for lactating dairy cows and suggests that dietary P requirements are independent of dietary Ca. [ABSTRACT FROM AUTHOR]

Twenty-four newborn Holstein heifer calves were fed 1 of 4 milk replacers (MR): control (20% CP, 21% fat; MR fed at 441 g/d); high protein/low fat (HPLF; 28% CP, 20% fat; MR fed at 951 g/d); high protein/high fat (HPHF; 27% CP, 28% fat; MR fed at 951 g/d); and HPHF MR fed at a higher rate (HPHF+; 27% CP, 28% fat; MR fed at 1,431 g/d). Dry calf starter (20% CP, 1.43% fat) composed of ground corn (44.4%), 48% CP soybean meal (44.4%), cottonseed hulls (11.2%), and molasses (1.0%) was offered free choice. Heifers were obtained from a commercial dairy, blocked by groups of 8 in the order acquired, and randomly assigned to treatments within group. Upon arrival at the research farm, heifers were fed the control for 2 feedings. Treatments were imposed when heifers were 4 ± 1 d of age. Heifers were on study for 61 ± 1 d. Body weight and body size measures were taken weekly. Four-day total collection of feed refusals, feces, and urine was initiated at 57 ± 1 d of age. Heifers were slaughtered at the end of the collection period to evaluate body composition. Preplanned contrasts were used to compare control to all, HPLF to HPHF, and HPHF to HPHF+. Heifers fed the control diet consumed more starter than those fed other treatment diets, but their total dry matter intake and apparent dry matter digestibility were lowest. Fecal output was highest in heifers fed the control diet, whereas urine output and urine N excretion were lowest. Nitrogen intake and urine N excretion were greater for heifers fed HPHF+ compared with HPHF but were not affected by MR fat content (HPLF vs. HPHF). Retention (g/d) of N and P was greater in heifers fed all nutrient-dense diets compared with those fed the control diet, but was not improved by increasing fat in the milk replacer (HPLF vs. HPHF) or by increasing the amount fed. Addition of fat to the milk replacer (HPLF vs. HPHF) increased empty body weight fat content without improving average daily gain or frame measures. Increasing the volume fed (HPHF vs. HPHF+) increased growth rate and empty body weight, but HPHF+ heifers were neither taller nor longer and their carcasses contained more fat. Clear improvements in growth and nutrient retention were observed with more nutrient-dense diets, but most of the improvements were seen with the increased protein intake relative to the control MR; adding fat to the high protein MR did not further improve lean tissue gain. [ABSTRACT FROM AUTHOR]

Twenty-seven multiparous Jersey cows were randomly assigned to receive an oral bolus containing corn starch (control, CON), corn starch plus 15 mg of 25-hydroxyvitamin D3 (25-OH), or 15 mg of cholecalciferol (D3) at 6 d before expected parturition. Cows were maintained in individual box stalls from 20 d before expected parturition and fed a common diet. Jugular blood samples were collected at -14, -13, -5, -4, -3, -2, -1 d before expected calving, at calving, and at 1, 3, 5, 7, 9, 11, 13, 28, 56, and 84 d postcalving. After calving, cows were housed in 1 pen in a free-stall barn and consumed a common diet. Colorimetric assays were used to analyze Ca, P, and Mg concentrations in serum. Serum concentrations of osteocalcin (OC), an indicator of bone formation, serum 25-hydroxyvitamin D3, and parathyroid hormone (PTH) were determined in samples obtained from d -5 through d 13. The 9 control multiparous cows and 5 untreated primiparous cows were used to evaluate the effect of parity on the variables that were measured. There was no effect of parity on Ca, PTH, or 25-OH concentration. Compared with second-lactation cows and older cows (>2 lactations), first-lactation cows had greater serum OC (22.3, 32.0, and 48.3 ng/mL, respectively), indicating that younger animals were forming more bone. Blood Ca, P, and Mg decreased near the time of calving and then increased over time. Serum 25-hydroxyvitamin D3 was greater for cows dosed with 25-OH (119.0 ng/mL) compared with those dosed with D3 (77.5 ng/mL) or CON (69.3 ng/mL). Cows dosed with 25-OH tended to have lower serum PTH concentration, but treatments did not affect serum Ca, P, or Mg. Serum OC was greater in second-lactation cows compared with cows entering their third or fourth lactation but OC was unaffected by treatment. Although results indicated a 60% increase in serum 25-hydroxyvitamin D3 due to a single oral dose of 25-OH before calving, the amount administered in this study apparently was not sufficient for initiation of any improvement in Ca homeostasis at parturition. [ABSTRACT FROM AUTHOR]

A dynamic, mechanistic, compartmental model of phosphorus (P) digestion and metabolism was constructed in the Advanced Continuous Simulation Language using conservation of mass principles and mass action kinetics. Phosphorus was assumed to exist in 3 forms: inorganic (Pi), phytic acid (Pp), and organic (excluding phytic acid; Po). All 3 forms were assumed to be present in the digestive tract with absorption of Pi into blood. Inputs to the model were total P intake; Pp, Po, and Pi as proportions of total P; milk yield; rate of salivation (fixed at 239 L/d); and rate of liquid passage from the rumen (fixed at 198 L/d). The model was fitted to 2 experiments from the literature. Derived parameters were well defined by the data. With a mean' observed P intake of 75 g/d, total tract P digestibility was 38%. Phytic acid P digestibility in the rumen was 74%, with no additional Pp digestion in the lower tract. Inorganic P and Po digestibility in the lower tract were 48 and 89%, respectively. Flows of Po and Pi from the rumen were 2.4 and 3.0 times greater than intake, respectively. The increase in Po was apparently due to microbial growth. The increase in Pi arose primarily from secretion of Pi into the rumen via salivation where 65% of absorbed P was recycled to the rumen. Milk synthesis used 30% of absorbed Pi, and 1% was excreted in urine. This research suggested that the primary regulation points for maintaining blood P were bone deposition and resorption and absorption from the intestine. However, because bone P balance was related to both dietary P intake and ruminal phytase activity, it is critical to achieve a better understanding of phytate digestibility across several feeds if dietary P is to be reduced below current requirements. [ABSTRACT FROM AUTHOR]

Monitoring or accurately predicting manure quantities and nutrient concentrations is important for dairy farms facing strict environmental regulations. The objectives of this project were to determine the daily outflow of manure nutrients from a free-stall barn using mass balance and to compare results with published excretion models. The project was conducted at the free-stall facility housing the lactating cow herd of the Virginia Tech Dairy Center in 2005. The herd consisted of 142 (±8.9) Holstein and Jersey cows with a mean body weight of 568 (±6.2) kg and average milk yield of 29.8 (±1.7) kg/d with 3.18% (±0.07) true protein and 3.81% (±0.13) milk fat on 18 sampling days. The intakes of dry matter (DM), N, and P were estimated from the formulated ration. Daily consumption averaged 21.7 (±0.27) kg of DM with 17.7% (±0.26) crude protein and 0.46% (±0.03) P. Approximately 110 (± 27.9) kg/d of sawdust was used as bedding; its contribution to manure flow was subtracted. The alleys in the free-stall barn were flushed every 6 h with recycled wastewater, and the slurry was collected. On 18 sampling days the volumes and constituents of the flushwater and the flushed manure were determined for a 6-h flush cycle and extrapolated to daily values. Net daily flow of solids and nutrients in manure were calculated as the differences between masses in flushed slurry and flushwater. Nitrogen and P excretion were also calculated from dietary inputs and milk output. The flow was compared with the American Society of Agricultural Engineers' (ASAE) standards. Each cow produced 5.80 kg/d of total solids (remainder after drying at 105°C). The ASAE standard predicted DM (remainder after drying at 60°C) excretion of 8.02 to 8.53 kg/d per cow. Recovery of P amounted to 74.8 g/d per cow. Overall, 102% of intake P was recovered; 75.1% in the manure outflow and 26.9% in milk. About 285 g/d and 148 g/d of N per cow were recaptured in manure and milk, respectively; 182 g/d was presumably volatilized. All models of N excretion appeared to underestimate N excretion. Volatilization rate of N amounted to 18.1%/h for the 6-h flush interval. Measured outflow of manure-P from the facility was similar to excretion predictions. Presentation of excreted solids as both total solids and DM is warranted. We conclude that using excretion prediction equations is useful for predicting excretion and outflow of P in a lactating cow facility, but N excretion predictions exhibited bias and have to be used prudently for predicting N outflow and N volatilization. [ABSTRACT FROM AUTHOR]

The objectives of this study were to evaluate the effects of limit feeding diets containing concentrates or by-products in place of forages on manure and nutrient excretion in growing, gravid heifers. Eighteen Holstein heifers confirmed pregnant were grouped by due date and fed 1 of 3 diets (n = 6 per treatment) for the last 14 wk of pregnancy. Diets were high forage, fed ad libitum (HF); by-product based (BP), fed at the same rate as HF-fed heifers; or low forage (LF), fed at 86% of the HF diet. Diets were designed to supply equal quantities of P, N, and metabolizable energy. Total collection of feces and urine was conducted in wk 14, 10, 6, and 2 prepartum. The HF ration was 90.7% forage, 13.7% crude protein (CP), and contained orchardgrass hay, corn silage, corn grain, soybean meal 44%, and a vitamin-mineral premix. The BP diet was 46.2% forage and 14.0% CP, with 70% of the grain mix space replaced with soybean hulls and cottonseed hulls in a 1:1 ratio, with intake limited to 93% of the dry matter intake (DMI) of HF. The LF ration was 45.3% forage and 17.8% CP, with intake limited to 86% of the DMI of HF. The effect of diet was analyzed with repeated measures, using preplanned contrasts to compare HF with BP and LF with HF and BP. As designed, heifers fed HF and BP had greater DMI than the heifers limit-fed LF, and there was no effect of diet on average daily gain or BW. Intake and digestibility of N were lower, and fecal N excretion was higher, in heifers fed HF and BP than heifers fed LF. Mean feces excretion on both a wet and dry basis was greater for HF heifers compared with BP heifers and less for LF heifers than for HF and BP heifers. Despite differences in urinary output, diet had no effect on urea N excretion, but there was a trend for heifers fed HF and BP rations to excrete less urinary N compared with those fed LF. Compared with HF and BP heifers, LF heifers tended to have lower fecal P excretion and had higher urinary P excretion. Measured manure and urine excretion from heifers fed LF was greater than current American Society of Agricultural and Biological Engineers values, whereas heifers fed HF excreted less manure and urine than predicted. Heifers achieving similar rates of gain from diets differing in forage, grain, and by-product content excreted widely varying quantities of manure. [ABSTRACT FROM AUTHOR]

The effect of an exogenous phytase and cellulase-containing enzyme formulation on nutrient digestibility and excretion was evaluated in 24 Holstein cows. Cows were fed corn silage- and alfalfa silage-based diets with or without a cellulase-phytase blend for 31 d in a continuous random design. Treatment groups were balanced for parity, days in milk, and mature-equivalent projected milk yield. Diets contained 37% forage, 18.3% crude protein, 35.4% neutral detergent fiber, 18% acid detergent fiber, and 0.42% P (no supplemental P). Cows were fed once daily in Calan doors and milked 2 times daily. Body weight and milk yield were recorded at each milking. Milk samples were collected on d 28 to 31 at 8 consecutive milkings. On d 28 to 31, fecal grab samples were collected every 8 h, with sampling times advanced by 2 h each day. Feces samples were pooled by cow. Feed and feces samples were analyzed for acid detergent lignin (used as an internal marker) and for N, P, neutral detergent fiber, and acid detergent fiber. Days in milk were similar between treatments, and body weight and milk yield were unaffected by treatment. Cows fed the enzyme formulation had reduced fecal dry matter, neutral detergent fiber, and acid detergent fiber excretion and reduced fecal excretion of N and P. Apparent digestibility of dry matter, acid detergent fiber, neutral detergent fiber, and N tended to increase with the enzyme formulation. Addition of an exogenous phytase and cellulase enzyme formulation to diets for lactating cows reduced fecal nutrient excretion. [ABSTRACT FROM AUTHOR]

Water quality in the United States is threatened by contamination with nutrients, primarily nitrogen (N) and phosphorus (P). Animal manure can be a valuable resource for farmers, providing nutrients, improving soil structure, and increasing vegetative cover to reduce erosion potential. At the same time, application of manure nutrients in excess of crop requirements can result in environmental contamination. Concentrated animal agriculture has been identified as a significant source of nutrient contamination of surface water, nitrogen contamination of groundwater, and ammonia emission. Areas facing the dilemma of an economically important livestock industry concentrated in an environmentally sensitive area have few options. If agricultural practices continue as they have in the past, despite the significant changes in agricultural intensity and changing environmental conditions, continued damage to water resources and a loss of fishing and recreational activity are inevitable. If agricultural productivity is reduced, however, the maintenance of a stable farm economy, a viable rural economy, and a reliable domestic food supply are seriously threatened. The identification and implementation of solutions to the generation of excess manure in confined animal feeding operations are necessary to enable such agricultural operations to thrive in environmentally sensitive areas such as the Chesapeake Bay Watershed. This paper will review an innovative collaborative approach to the development of a manure and litter solutions strategy by a diverse array of potential problem-solvers. [ABSTRACT FROM AUTHOR]

The objectives of this investigation were to assess the relationship between chemical measures and imaging estimates (radiographic photometry and dual-energy x-ray absorptiometry) of bone mineral content in dairy cows and to evaluate the effects of parity, stage of lactation, and site of measurement (fused third and fourth metacarpal bone vs. caudal vertebrae 14 and 15) on bone mineral content. In a preliminary study, the caudal vertebrae were excised from 33 cows following slaughter. Samples were analyzed by radiographic photometry and then analyzed for mineral content chemically. In a second experiment, the caudal vertebrae and right front metacarpal (sample pairs) were excised from 107 Holstein cull cows following slaughter. Parity and days in milk (DIM) of the donor animals were obtained for 43 pairs of samples. Samples were grouped by parity (1, 2, 3, and ≥4) stage of lactation (Stage 1: <90 DIM, Stage 2:90 to 150 DIM, Stage 3:151 to 250 DIM, and Stage 4: >250 DIM). Samples were analyzed by radiographic photometry and dual-energy x-ray absorptiometry and then analyzed for mineral content chemically. In both experiments, the relationship between mineral content estimated via the imaging techniques and mineral content measured chemically was poor, likely because of the relative maturity of animals in the sample set and lack of variation in mineral content. Ash content was higher in the metacarpal than in the caudal vertebrae, as were concentrations of Mg (expressed as a proportion of bone ash). No effects of stage of lactation were observed on bone mineral in the caudal vertebrae, but in the metacarpal, P content (proportion of total mineral) was highest in second lactation cows. Total bone mineral content (ash) was not affected by parity in the metacarpal or caudal vertebra, but Ca and P content of the metacarpal increased with parity. Noninvasive imaging techniques are not sufficiently sensitive to detect changes in mineral content or composition... [ABSTRACT FROM AUTHOR]

The objective of the study was to evaluate the effect of forage and non-flber carbohydrate content on duodenal and fecal P flow. Eight Holstein cows (4 primiparous) fitted with ruminal and duodenal cannulae were fed diets containing either 60 or 35% forage and either 30 or 40% NFC in a 2x2 factorial with a replicated 4x4 Latin square design. Dietary P content (% DM) was 0.0.36, 0.36, 0.35, and 0.36 for 60:30, 60:40, 35:30 and 35:40 respectively. Duodenal digesta and feces were collected for 3 d at the beginning of wk 3, every 3 h, advanced 1 h/d. Samples were composited by cow within period and analyzed for total P. Increasing dietary forage content decreased P intake and fecal P excretion, and salivary P flow (daily duodenal P - P intake) tended to increase with increased forage (49.9 vs. 55.8 g/d, P < 0.11). Duodenal P flow and apparent P digestibility were unaffected by forage content. Increasing dietary NFC content increased P intake and increased apparent P digestibility (32.8 vs. 41.5%; P < 0.02). Cows were in negative P balance but cows fed high NFC diets had less negative P balance. In a subset of samples (4 cows fed diets with 40% NFC and 60 or 35% forage in sequential 3 wk periods), P compounds were extracted with 0.1M NaOH-EDTA and quantified by NMR spectroscopy. Duodenal digesta was higher in orthophosphate, pyrophosphate and lipid phosphate concentration than were feces. Concentration of myo-inositol hexakisphosphate (IHP, or phytic acid) was higher in feces, but duodenal and feces IHP flows were similar. Concentration and flow of "other" P (primarily degradation products of IHP) was higher in duodenal digesta than in feces, indicating post-ruminal degradation. Increasing dietary forage increased orthophosphate concentration in both duodenal digesta and feces, but flow of ortho-P was unaffected by diet. Increased understanding of form and amount of P flow through the digestive tract will support refinements to more accurately match absorbable P supply to P requirements of the lactating cow. [ABSTRACT FROM AUTHOR]

Only 25 to 35 % of the crude protein (CP) consumed by dairy cows is converted into milk. Such poor use of dietary CP may be due to inefficiencies associated with forage nitrogen (N) capture and metabolism. Manure N excreted in feces and urine, and the transformation of manure N in air, soil and crops are highly influenced by what dairy cows consume. For example, reducing dietary CP resulted in less total manure N, especially urine N excretion. Ammonia loss from manure from a low CP diet (13.6%) was lower than from a high CP diet (19.4%), representing 9 and 25% of applied manure N, respectively. Increasing condensed tannin content of dietary forage legumes also reduced urine N excretion. Ammonia emissions from barn floors were greater from manure derived from alfalfa silage (AS)-based diets than either birdsfoot trefoil with low or high tannin levels. After application to soil, feces from cows AS-based diets generally lead to higher soil inorganic N (IN) levels than soils amended with feces from corn silage-based diets; feces from AS-based diets increased plant yield and N uptake; feces from high CP diets resulted in greater soil IN levels than feces from low CP diets; and feces from low CP diets did not increase soil IN but decreased plant yield and N uptake. Only a small increase in N efficiency is necessary to make substantial reductions in the dairy industry's contribution to the environmental N load. There appears to be a range of dietary options that satisfy the nutritional requirements of high-producing dairy cows, yet produce manure that has differential effects on post-excretion transformations and environmental losses. Dairy production efficiencies may be gained and manure N losses reduced by incorporating moderate levels of tannins or other protein protection compounds into forages to enhance CP use and reduce dietary CP concentrations, and by developing perennial forages that tolerate manure applications, have improved ammonia absorption and assimilation potential, and are able to assimilate excess soil nitrates. [ABSTRACT FROM AUTHOR]

The objective of the study was to evaluate the effect of increasing dietary beet pulp (BP) content on duodenal and fecal flow of total phosphorus (P) and phytic-acid (PA) P. Eight multiparous Holstein cows fitted with ruminal and duodenal cannulae were fed diets containing 40% forage (corn silage and alfalfa silage) and 0, 6.1, 12.1 or 24.3% unmolassed, pelleted BP (replacing high moisture corn grain on a DM basis) in a replicated 4x4 Latin square design with 21-d periods. The nutrient content of BP averaged 39.9% NDF, 8.9% CP, 8.0% indigestible NDF, 3.9% starch, and 0.29% free glucose on a DM basis. Duodenal digesta and feces were collected every 9 h on d 12-14, and rumens were evacuated and subsampled 4 h after feeding on d 20 and 2 h before feeding on d 21. Samples were composited by cow within period and analyzed for P (nitric/perchloric digestion) and PA-P (anion-exchange method). Linear and quadratic effects of increasing BP content were analyzed using Proc Mixed of SAS. Dietary P and PA content were reduced linearly with increasing percent BP (0.59, 0.58, 0.57, 0.56 %P and 0.15, 0.14, 0.13, 0.11 %PA, respectively). With increasing BP content, P intake, ruminal P content, and rumen P pool size decreased. Digestion, duodenal flow and fecal excretion of P were not affected. With increasing dietary BP content, PA intake was reduced, ruminal pool size was reduced, and rumen turnover time (h) was increased. Apparent ruminal digestibility of PA was decreased linearly with increasing BP (36.5, 31.8, 24.6, 13.6 %; P < 0.02), and apparent total tract PA digestibility was similarly affected (85.3, 82.7, 82.1, 79.1%; P < 0.01). As previously reported, increasing BP was associated with reduced ruminal starch digestion and increased post-ruminal starch digestion. Fecal excretion of PA-P averaged 5.2 g/d. Replacing starchy grains with BP reduced digestion of PA-P, and the majority of the disappearance of PA-P occurred post-ruminally. [ABSTRACT FROM AUTHOR]

Data were collected for one year from a working manure system consisting of a mechanical screen separator, gravitational settling basin (SB), and three aerated storage tanks in series. The manure from 140 lactating dairy cows was flushed with ~ 40,000 L recycled wastewater four times per day. The blend was separated to solid and liquid portions by a mechanical solid-liquid manure separator consisting of two concave screens, pore size 0.79 mm (screen 1) and 3.18 mm (screen 2). The liquid portion flowed into a SB and by gravity into the first aerated tank (pump power: 5 kg O2/h). The wastewater was pumped into sequential aerated tanks, with the third tank supplying the flush water. Composite samples of flushed slurry and effluents from the separator, SB, and tanks 1, 2, and 3 were taken every other week (n=14) and then monthly (n=7). Weighted results were analyzed using Proc Mixed with site and date in the model and date as a repeated measure. Mechanical separation of the blend, including the solids and nutrients from the flushwater, reduced total (TS) and volatile solids (VS) by 19 and 25%, total Kjehldahl N (TKN) by 9%, total P (TP) by 18%, and chemical oxygen demand (COD) by 17%. The SB reduced TS by 11%, VS by 12%, and TKN and TP by 10%. The combined effect of aeration and settling in tanks 2 and 3 decreased TS and VS by 22% and 24%, respectively. Nitrates, TKN, and TP were reduced by 49%, 14%, and 13%. Ortho-P and nitrite concentrations remained steady. The combined tanks reduced COD by 21%, while dissolved oxygen increased from 0.4 to 1.1 mg/l, and the oxidation-reduction potential rose from -230 to 16 mV. Separation of flushed dairy manure with subsequent settling and aeration effectively removed particles and nutrients from the wastewater. Aeration improved dissolved oxygen content and oxidation-reduction potential. [ABSTRACT FROM AUTHOR]

The objectives were to monitor for one year final irrigation water after separation of solids, and settling and aeration in three tanks on a 140-cow flushed freestall dairy with sawdust bedding. The flushed slurry was separated (screen sizes 0.79 and 3.18 mm). The liquid flowed into a 400 m3 settling basin, then via gravity into a tank (2.3 Dm3), and was pumped into the next two successive tanks (2.3 and 4.3 Dm3). The third tank provided the flush and irrigation water. An aerator (pump volume: 5 kg O2/h) supplied air at a surface depth of 45 cm in each tank. On 21 dates volumes and constituents of the flushwater were determined, and the effects of period (Nov. to Apr. 2005, Apr. to July 2005, Aug. to Dec. 2005) on its composition were analyzed using Proc GLM in SAS. The manure system was primed with 5 Dm3 fresh water at startup (July 2004). Daily fresh water input ranged from 34 to 56 m3. Concentrations of solids and nutrients were lowest in the first period. The tanks were pumped down dramatically in Apr. Total, total suspended, volatile, and volatile suspended solids concentrations rose 3, 9, 4, and 8-fold in period two (13.7, 10.9, 9.4, and 8.5 g/l), and dropped in period three (7.0, 3.6, 3.9, and 3.0 g/l, respectively). Total P (63, 253, 147 mg/l), total Kjeldahl N (425, 986, 594 mg/l), and chemical oxygen demand (2.5, 13.5, and 5.4 g/l) were lowest in period one, and highest in period two. Nitrate (0.62 mg/l), nitrite (6.73 μg/l), and pH (8.0) did not change. Dissolved O2 (1.40, 0.35 and 2.05 mg/l) and oxidation-reduction potential (84, -110, and 47 mV) were lowest in period two. Low initial concentrations were likely due to dilution. After perturbation it took four months for solid and nutrient concentrations to decline and stabilize. Continued sampling will be used to assess whether the values observed since Aug, 2005 are sustainable values for this system. [ABSTRACT FROM AUTHOR]

Manure and its nutrient concentrations are important in meeting environmental regulations. This project determined the daily production of manure at the Virginia Tech Dairy in 2005. The herd consisted of 140 Jerseys, Holsteins, and crossbreds, with a mean bodyweight of 560 kg, and averaged 30.1 kg/d milk with 3.16% true protein. The intake of N and P was estimated from the formulated TMR, allowing for a 3% feed refusal. Approximately 103 kg/d of sawdust were used as bedding. The alleys in the freestall barn were flushed every 6 h with recycled wastewater and the slurry was collected. On 17 dates the volumes and constituents of the flushwater and the flushed manure were determined during a 6 h flush cycle. One sampling showed outlying results and was eliminated from the analysis. Net daily accumulations of solids and nutrients from the manure were calculated as the differences between masses in flushed slurry and flushwater. These results were compared with ASAE Standards for "Manure Production and Characteristics" with the Students t-test. Total (TS) and volatile solids (VS) per cow were 6.4 and 5.3 kg/d with bedding, and 5.7 and 4.6 kg/d without bedding. Production of TS and VS without bedding differed from the standards, but VS as a percentage of TS (84%) did not. Daily chemical oxygen demand was similar to the ASAE prediction of 6.2 kg/cow. Total Kjeldahl N (289 g/d), ammonia-N (144 g/d; n=12), and P (77 g/d) accumulations per cow were higher than predicted. Recovery in slurry of the P in feed and bedding minus P in milk was 93%. Recovery of N averaged 59%. Assuming a constant N loss from manure, N loss was 4.3%/h. Assuming that 60% of the manure N was in urine, the urinary N volatilization rate was 15.5%/h. These results showed less than predicted production of TS and VS in the manure of lactating dairy cows and provide a practical estimate of N volatilization and P recovery. [ABSTRACT FROM AUTHOR]

The effect of exogenous phytase + cellulase (CattleAse P™) on nutrient digestibility and excretion was evaluated in 46 Holstein cows (n=23 per trt). Cows were fed corn silage and alfalfa silage based diets with or without a cellulase-phytase blend for 31 days in a CRD. Treatment groups were balanced for parity, days in milk and M.E. projected milk yield (mean = 2.2, 100 and 25,574, respectively). Diets were 37% forage, 18.3% CP, 35.4% NDF, 18% ADF, and 0.42% P (no supplemental P). Cows were fed 1X in Calan doors and milked 2X. Body weight and milk yield were recorded at each milking. Milk samples were collected on d 28 to 31 at 8 consecutive milkings. On d 28 to 31, fecal grab samples were collected from 24 cows (12 per treatment) every 8 h, with sampling times advanced by 2 h each day. Feces samples were pooled by cow. Feed and feces samples were analyzed for sulfuric acid lignin (used as an internal marker) and for N, P, ADF, and NDF. Effect of diet on milk yield and components, body weight, and feed intake was analyzed using PROC Mixed with day as a repeated measure. The effect of treatment on nutrient digestibility and excretion were analyzed with PROC GLM. The phytase + cellulase tended to increase milk yield efflciency (1.68 vs. 1.77 kg milk/kg feed) and milk urea N content was lower in cows fed the enzyme. DMI tended to be lower in cows fed the enzyme (24.4 vs. 22.8 kg/d; P < 0.10), and body weight and milk yield were unaffected by treatment. During the feces collection period (d 28-31) DMI was similar between treatments (25.5 kg/d), and cows fed the enzyme formulation had reduced feces DM excretion (9.55 vs. 7.66 kg/d; P < 0.01) and reduced fecal excretion of N (252 vs. 203 g/d; P < 0.01) and P (66.9 vs. 55.2 g/d; P < 0.01). Apparent digestibility of DM, ADF, NDF, and N tended to increase with the enzyme formulation. Utilization of an exogenous phytase + cellulase formulation reduced fecal nutrient excretion by lactating cows. [ABSTRACT FROM AUTHOR]

Twenty-four newborn Holstein heifer calves (n=6) were fed one of four diets: CON (20/20 fed at 450 g/d, 24%CP, 0.53%P); HP (28/20 fed at 970 g/d, 32%CP, 0.55%P); HFHP- (28/28 fed at 970 g/d, 32%CP, 0.46%P); and HFHP+ (28/28 fed at 1460 g/d, 32%CP, 0.46%P). Calves were grouped by age and treatments were assigned randomly within group. Calves were fed 3.4 L of colostrum twice within 16h of birth. Upon arrival at the research farm, calves were fed a 20/20 milk replacer for the first two feedings. On d 3, treatments were imposed and calf starter (20% CP, 0.48%P) comprised of corn (40%), soybean meal (40%) and cottonseed hulls (20%) was offered free choice. Calves were on study for ~63 d. Total collection of feed refusals, feces and urine were initiated on d 59 ± 2d. Body weight and body size measures were taken weekly. Feces, urine, milk replacers, and starter samples were pooled (25% of each daily sample) by calf or diet, respectively, across collection period and analyzed for total Kjeldhal N and total P. All calves were slaughtered at 63 d to evaluate additional tissues (reported elsewhere). Preplanned contrasts were used to compare CON to all, HP to HFHP-, and CON to HFHP-. Total DMI was not different as calves fed CON consumed more starter than those fed greater amounts of milk replacer. Apparent DMD was lower for calves fed CON. Fecal output (kg DM/d) and fecal N excretion were highest in calves fed CON while urine output (kg/d) and urine N excretion were lowest. Nitrogen intake and urine N excretion were highest for calves fed HFHP+ but were not affected by fat content (HFHP- vs. HP). Nitrogen retention was not improved by increasing energy intake (mean = 34.9%), however, it was improved by increasing N intake (CON vs. HP; 20.5 vs. 38.2%). Phosphorus digestibility, total excretion, partitioning, and retention were not impacted by treatment. Calves fed HP tended to have higher P retention compared to those fed CON. Milk replacer composition influenced nutrient excretion in pre-weaned calves. [ABSTRACT FROM AUTHOR]

The objective of the current work was to use digestion coefficients from the Feng et al. (2015) model (Virginia Tech model) to calculate P bioavailability of common feeds used in dairy production. Compared with the bioavailability calculated by the Virginia Tech model, using the NRC (2001) P absorption coefficient of 0.64 for forages would underestimate the bioavailabilities of alfalfa hay, alfalfa silage, corn silage, grass hay, and mixed mainly legume silage. For concentrates, using the NRC (2001) P absorption coefficient of 0.70 would overestimate the bioavailabilities of corn grain but underestimate bioavailability of high-moisture corn. Two dairy diets were formulated using nutrient values from the NRC (2001): a standard diet that includes minimal by-products, and a by-product diet that has reduced corn and soybean meal which was replaced with corn gluten feed, distillers grains, hominy feed, and wet brewers grains. For each diet, total bioavailable P was calculated using availability values from the NRC (2001) and the Virginia Tech model. Comparison of P balance (the difference between required and bioavailable P) for each diet was made using the 2 sets of bioavailabilities for a reference cow weighing 682 kg, producing 38.6 kg of milk/d (3.5% fat and 3.0% true protein, 100 d in milk), and consuming 23 kg of dry matter/d, yielding an absorbed P requirement of 59.4 g/d. The standard diet supplied 56.69 and 53.52 g of bioavailable P per day using bioavailabilities from the NRC (2001) and Virginia Tech models, respectively, resulting in a P balance of -2.71 and -5.88 ± 0.26 g/d. The by-product diet provided 75.75 and 78.47 g/d of bioavailable P, yielding P balances of 16.35 and 19.07 ± 0.37 g per day, respectively, using the 2 sets of bioavailabilities. Using P bioavailabilities for individual ingredients that were based on the Virginia Tech model resulted in different bioavailable P levels thus resulted in differing dietary P balances in a field setting. [ABSTRACT FROM AUTHOR]

The composition of water given to dairy cattle is often ignored, yet water is a very important nutrient and plays a major role in milk synthesis. The objective of this study was to study effects of elevated levels of iron in bovine drinking water on milk quality. Ferrous lactate treatments corresponding to 0, 2, 5, and 12.5 mg/kg drinking water concentrations were delivered through the abomasum at 10 L/d to 4 lactating dairy cows over 4 periods (1 wk infusion/period) in a Latin square design. On d 6 of infusion, milk was collected, processed (homogenized, pasteurized), and analyzed. Mineral content (Fe, Cu, P, Ca) was measured by inductively coupled plasma mass spectrometry. Oxidative stability of whole processed milk was measured by the thiobarbituric acid reactive substances (TBARS) assay for malondialdehyde (MDA) and sensory analysis (triangle test) within 72 h of processing and after 7 d of storage (4°C). Significant sensory differences between processed milks from cows receiving iron and the control infusion were observed. No differences in TBARS (1.46 ± 0.04 mg of MDA/kg) or mineral content (0.22 ± 0.01 mg/kg Fe) were observed. A 2-way interaction (iron treatment by cow) for Ca, Cu, and Fe concentrations was seen. While iron added directly to milk causes changes in oxidation of milk, high levels of iron given to cattle have subtle effects that initially may not be obvious. [ABSTRACT FROM AUTHOR]

The objective was to evaluate the effect of dietary phytate P (Pp) supply on ruminal and postruminal Pp digestion and net disappearance of P from the lower digestive tract of lactating cows. Six ruminally and ileally cannulated crossbred lactating cows were used in 2 incomplete Latin squares with four 21-d periods (17 d of diet adaptation, 4 d of total collection). Dietary treatments were low Pp, medium Pp, and high Pp, and a high inorganic P (Pi) diet with the same total P content as the highest Pp diet but with P mostly from inorganic sources. The diets contained 0.10, 0.18, 0.29, and 0.11% Pp and 0.43, 0.48, 0.54, and 0.53% total P on a dry matter basis, with cottonseed meal used to increase Pp content. Ytterbium-labeled corn silage and Co-EDTA were used as particulate and liquid phase markers to measure omasal and ileal digesta flow. Omasal and ileal digesta were collected every 6 h on d 20 and 21 and rumen contents were collected on d 21. Samples were analyzed for total P (molybdovanadate yellow method), Pi (blue method), and Pp (high performance ion chromatography). Phytate P and total P intake increased linearly with increasing dietary Pp. Ruminal Pp disappearance also increased linearly with dietary Pp but the magnitude of change was small. Small intestinal net disappearance of Pi was not affected by dietary Pp. Phytate P was hydrolyzed in the large intestine but its hydrolysis was not influenced by dietary Pp. Net disappearance of Pi form the large intestine did not vary with dietary Pp. Dry matter digestibility decreased linearly with increasing dietary Pp, as did apparent digestion of P, and fecal P increased linearly. Dry matter digestibility was higher for high Pi than for high Pp, likely due to the effect of cottonseed meal in the latter diet. Replacing a portion of Pp with Pi resulted in decreased P excretion but this effect was confounded with increased fecal dry matter for the high-Pp (high-cottonseed meal) diet. In lactating cows Pp digestibility was not negatively influenced by dietary Pp and fecal P excretion was regulated by dietary total P rather than by form of dietary P. [ABSTRACT FROM AUTHOR]

We investigated the effects of increasing dietary protein and energy on concentrations of selected blood metabolites and hormones in Holstein heifers. Twenty-four heifers were fed 1 of 4 milk replacer (MR) diets for 9 wk (n = 6/diet): control [20% crude protein (CP), 21% fat MR fed at 441 g of dry matter (DM)/d], HPLF (28% CP, 20% fat MR fed at 951 g of DM/d), HPHF (27% CP, 28% fat MR fed at 951 g of DM/d), and HPHF+ (27% CP, 28% fat MR fed at 1,431 g of DM/d). Heifers were fed twice daily; water and starter (20% CP, 1.43% fat) were offered free choice and starter orts recorded daily. Serum and plasma aliquots from blood samples collected twice weekly after a 12-h fast were analyzed for insulin-like growth factor (IGF)-I, IGF-binding proteins (IGFBP), growth hormone (GH), insulin, glucose, nonesterified fatty acids, triglyceride, and plasma urea nitrogen concentrations. Only plasma glucose, IGFBP-2, and IGFBP-3 were affected by diet. Dietary treatment differences were only noted when the control was compared with the average of the other 3 diets. The addition of fat to the MR (HPLF vs. HPHF) and increased volume of MR (HPHF vs. HPHF+) had no effect on plasma glucose concentration or relative abundance of IGFBP- 2 or IGFBP-3. Heifers fed the control diet had less glucose, greater IGFBP-2, and less IGFBP-3 than the average of the other 3 diets. There was a diet by week interaction for IGF-I. Serum IGF-I concentration in control heifers varied in a quadratic manner with a nadir (20 ± 4 ng/mL) at wk 4, whereas IGF-I increased linearly in heifers on other diets. Both insulin and triglyceride changed over time in a complex pattern (significant linear and quadratic contrast effects). The greatest concentrations were measured at wk 0.5 with nadirs at wk 6 for both insulin and triglyceride. Serum GH concentration decreased in a linear manner from wk 0.5 to wk 9 in all heifers. Relative abundance of IGFBP-2 was quadratic over time with the greatest amount of IGFBP-2 observed at wk 5. With the exception of glucose, IGF-I, IGFBP-2, and IGFBP-3, the blood variables measured were not influenced by treatment. The IGF-I-GH-IGFBP axis requires further study in heifers to deduce effects of nutrition on hypothalamic regulation of metabolism. We expected to see more treatment differences in concentrations of metabolites involved with protein and fat metabolism. It is likely that the diets used in this study were not diverse enough in composition to elicit such changes or that the efficiency of use of absorbed protein and fat was not different in these animals. [ABSTRACT FROM AUTHOR]

The effect of starch source and phytic acid (PA) supplementation on phosphorus (P) partitioning and ruminal phytase activity was evaluated in eight midlactation cows (four ruminally cannulated). Cows were randomly assigned to treatments in replicated 4 x 4 Latin squares with four 18-d periods. Diets included dry ground corn (DG) or steam-flaked corn (SF), with no supplemental P (L; 0.33% P) or supplemental purified PA (0.44% P) to provide additional P from a nonmineral source. Total collection of milk, urine, and feces was conducted on d 16 to 18 of each period. Ruminal fluid was sampled and ruminal pH measured every 8 h on d 17 and 18. Milk yield was unaffected by starch source, despite lower DMI by cows fed SF. Cows fed SF had increased DM digestibility compared with those fed DG, and tended to have higher efficiency of milk yield (1.40 vs. 1.35 kg of milk/kg of DMI). Intake and fecal excretion of P was lower in cows fed SF than in cows fed DG. In cows fed SF, milk P as a percentage of P intake increased compared with cows fed DG. Ruminal pH was unaffected by diet, but milk fat content was lower for cows fed SF. Milk yield, DMI, and feed to milk ratio were not affected by supplementation with PA. Although cows fed PA had increased P intake compared with cows fed low P diet, increased P excretion resulted in no differences in apparent P digestibility. Phosphorus balance tended to be higher in cows fed PA, but milk P as a percentage of intake was reduced. The interaction of starch source and PA affected ruminal phytase activity. Altering starch source to improve efficiency of milk yield in lactating dairy cows may help reduce P losses from dairy farms. [ABSTRACT FROM AUTHOR]

The effect of dietary P intake on intestinal P absorption was evaluated in growing Holstein steers. Diets varying in P content (0.15, 0.27, 0.36, and 0.45%, DM basis) were fed to 8 steers (174 ± 10 kg of BW) fitted with permanent duodenal and ileal cannulas in a replicated 4x4 Latin square with 14-d periods. Ytterbium-labeled corn silage and cobalt-EDTA were used as particulate and liquid phase markers, respectively, to measure digesta flow. Duodenal and ileal samples and spot urine samples were collected every 9 h from d 11 to 14. Total fecal collection was conducted on d 11 to 14 with fecal bags. Blood samples were collected from the coccygeal vessel on d 14. Feed, digesta, and fecal samples were analyzed for total P and inorganic P. Data were analyzed using PROC GLIMMIX in SAS with a model including treatment, square, period, and interaction of treatment and square. Preplanned contrasts were used to evaluate linear and quadratic treatment effects. Results were reported as least squares means. Dry matter intake (mean = 4.90 kg/d, 2.8% of BW) and apparent DM digestibility (mean = 78.1%) were unaffected by treatment. Duodenal and ileal flow of total P increased linearly with increasing P intake (13.4, 18.5, 23.0, and 27.4 g/d; 6.80, 7.87, 8.42, and 10.4 g/d). Increasing P intake increased the quantity of P absorbed from the small intestine linearly (6.96, 11.1, 14.6, and 17.2 g/d), but absorption efficiency was unchanged (mean = 59.6%). Phosphorus was absorbed on a net basis from the large intestine, but this was not affected by treatment and was a small proportion of total P absorption. Blood inorganic P increased linearly with increased dietary P (4.36, 6.31, 7.68, and 8.5 mg/dL) and salivary P secretion was unchanged (mean = 5.79 g/d), suggesting that rumen function was prioritized during short-term P deficiency. These data showing an absence of change in absorption efficiency and salivary P secretion in the face of short-term P deficiency may be used to improve published models of P digestion, absorption, and metabolism. [ABSTRACT FROM AUTHOR]

Accurate estimates of phosphorus (P) availability from feed are needed to allow P requirements to be met with reduced P intake, thus reducing P excretion by livestock. Exogenous phytase supplementation in poultry and swine diets improves bioavailability of P, and limited research suggests that this strategy may have some application in dairy cattle rations. The effects of exogenous phytase and forage particle length on site and extent of P digestion were evaluated with 5 ruminally and ileally cannulated lactating cows (188 ± 35d in milk). Cows were assigned in a 2 x 2 factorial arrangement of treatments in 2 incomplete Latin squares with four 21-d periods. Diets contained P slightly in excess of National Research Council requirements with all P from feed sources. During the last 4 d of each period, total mixed ration, refusals, omasal, ileal, and fecal samples were collected and analyzed for total P, inorganic P (Pi), and phytate (Pp). Total P intake was not influenced by dietary treatments but Pp intake decreased and Pi intake increased with supplemental phytase, suggesting rapid action of the enzyme in the total mixed ration after mixing. Omasal flow of Pi decreased with phytase supplementation, but we observed no effect of diet in ileal flow or small intestinal digestibility of any P fraction. Fecal excretion of total P was slightly higher and Pp excretion was lower for cows receiving diets supplemented with phytase. Milk yield and composition were unaffected by diets. When phytase was added to the mixed ration, dietary Pp was rapidly degraded before intake and total-tract Pp digestion was increased. The lack of effect of phytase supplementation on dietary P utilization was probably because these late-lactation cows had a low P requirement and were fed P-adequate diets. [ABSTRACT FROM AUTHOR]

Milk urea nitrogen (MUN) is correlated with N balance, N intake, and dietary N content, and thus is a good indicator of proper feeding management with respect to protein. It is commonly used to monitor feeding programs to achieve environmental goals; however, genetic diversity also exists among cows. It was hypothesized that phenotypic diversity among cows could bias feed management decisions when monitoring tools do not consider genetic diversity associated with MUN. The objective of the work was to evaluate the effect of cow and herd variation on MUN. Data from 2 previously published research trials and a field trial were subjected to multivariate regression analyses using a mixed model. Analyses of the research trial data showed that MUN concentrations could be predicted equally well from diet composition, milk yield, and milk components regardless of whether dry matter intake was included in the regression model. This indicated that cow and herd variation could be accurately estimated from field trial data when feed intake was not known. Milk urea N was correlated with dietary protein and neutral detergent fiber content, milk yield, milk protein content, and days in milk for both data sets. Cow was a highly significant determinant of MUN regardless of the data set used, and herd trended to significance for the field trial data. When all other variables were held constant, a percentage unit change in dietary protein concentration resulted in a 1.1 mg/dL change in MUN. Least squares means estimates of MUN concentrations across herds ranged from a low of 13.6 mg/dL to a high of 17.3 mg/dL. If the observed MUN for the high herd were caused solely by high crude protein feeding, then the herd would have to reduce dietary protein to a concentration of 12.8% of dry matter to achieve a MUN concentration of 12 mg/dL, likely resulting in lost milk production. If the observed phenotypic variation is due to genetic differences among cows, genetic choices could result in herds that exceed target values for MUN when adhering to best management practices, which is consistent with the trend for differences in MUN among herds. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the disappearance of phytate from the large intestine of dairy heifers. Uncertainty about the availability of phosphorus (P) in different feeds may limit implementation of dietary strategies to reduce fecal P excretion by dairy cows. Increased understanding of the dynamics of phytate degradation and disappearance of P in the large intestine may improve prediction of intestinal P digestion and absorption. Eight ruminally- and ileallycannulated crossbred dairy heifers were used in two 4 × 4 Latin square designs with 9-d periods, including 3 d of washout. All heifers were fed a high-forage diet containing 0.14% P throughout the study. Ytterbiumlabeled corn silage and Co-EDTA were dosed to the rumen 4 times daily as particulate and liquid phase markers, respectively, to measure ileal digesta flow. On d 4 to 7 of each period, each heifer was infused ileally with 0, 5, 15, or 25 g/d of phytate (phytic acid) in solution and total fecal collection was conducted. When infusion ceased (d 8 and 9) ileal digesta was sampled to measure P flow to the ileum from the basal diet. Feed, digesta, and feces were dried, ground, and analyzed for phytate P, inorganic P, and total P using high performance ion chromatography, inductively coupled plasma atomic emission spectroscopy, and the molybdovanadate yellow method, respectively. Phytate degradation in the large intestine was observed but was not complete, and the amount of infused phytate did not influence the degradability of phytate. Fecal excretion of total P increased with increasing total P infused. The slope coefficient for ileal P flow (dietary only) to feces was 0.56 ± 0.26 (mean ± SE), whereas the slope coefficient for infused P was 0.75 ± 0.13. These indicate net absorption of P from the large intestine and greater disappearance of P from dietary P flowing to the ileum than from the infused pure phytate (44 vs. 25%). This data will support mechanistic modeling efforts to improve prediction of P digestion, allowing more accurate estimation of P bioavailability in feeds. [ABSTRACT FROM AUTHOR]