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Selenium is an essential trace mineral for dairy cattle and can be provided in the diet in various forms that may differ in bioavailability. The objective of this study was to determine how source of Se affects animal performance, Se status, retention, and apparent and true absorption. Multiparous Holstein cows (n = 24; 597 ± 49 kg of BW) were blocked by DIM (161 ± 18) and randomly assigned to receive 0.3 mg Se/kg of DM (100% of National Academies of Sciences, Engineering, and Medicine requirements) of either organic Se (ORG; selenized yeast) or inorganic Se (INO; sodium selenite). The Se premix was top dressed on a common TMR fed daily and mixed into the top 15 cm directly before feeding. Following an 11-wk adaptation period, cows received simultaneous infusions of an intraruminal isotope dose of 77 Se in the same chemical form as the premix, and an intravenous dose of 82 Se in an inorganic form. Infusions were followed by a 4-d period of blood and rumen fluid sampling, and total collection of feces, urine, and milk. Daily DMI (23 ± 0.6 kg), milk yield (35 ± 1.2 kg), and serum Se (0.11 ± 0.003 µg/g) were not different between treatments during the adaptation period, but milk Se concentrations were greater for ORG compared with INO. Serum 77 Se maximum concentration and area under the curve (AUC) were not different between treatments for 72 h following infusion, but rumen fluid 77 Se AUC was higher for ORG than INO. Apparent absorption (64% ± 1.4%), and retention (44% ± 1.5%) of the 77 Se dose did not differ between treatments. True absorption was calculated using 82 Se enrichment in serum and feces and was determined to be 69% ± 1.3% and did not differ between treatments. Fecal excretion of the 77 Se dose was not different between treatments (36% ± 1.4%), but ORG had lower urinary excretion and higher milk excretion compared with INO. These results indicate that organic Se resulted in greater Se concentration of milk and lower urinary Se excretion into the environment, but absorption, Se status, and performance of the cow were not affected by Se source at this supplementation level., (© 2024, 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/).)

This randomized controlled trial investigated the effects of temporarily reducing milking frequency (MF) on the resolution of ketosis and milk production in dairy cows in early lactation. To detect ketosis [blood β-hydroxybutyrate (BHB) ≥1.2 mmol/L], Holstein cows were screened daily from 3 to 16 d in milk using a cow-side meter. Cows diagnosed with ketosis (n = 104) were randomly assigned to twice-daily milking (TDM) or reduced to once-daily milking (ODM) for 2 wk, then returned to twice-daily milking. Both treatment groups received a 5-d treatment of an oral propylene glycol drench (PG; 300 g) beginning on the afternoon of the diagnosis; cows received additional 5-d PG treatments if they had a ketotic test result (blood BHB ≥1.2 mmol/L) at least 4 d after finishing the first PG treatment. Blood BHB tests were conducted for the first 3 d after ketosis diagnosis, and then once every 3 d for 21 d of trial (DOT). Milk and milk component data were collected weekly for 15 wk following trial enrollment. The ODM group showed rapidly and markedly decreased blood BHB concentrations (primiparous cows: 1 DOT, 0.92 ODM vs. 1.22 TDM, 15 DOT, 0.55 vs. 0.81 mmol/L; multiparous cows: 1 DOT, 1.01 vs. 1.40, 15 DOT, 0.78 vs. 1.65 mmol/L). In addition, a logistic regression model indicated that ODM cows were less likely to have blood BHB concentrations ≥1.2 mmol/L [primiparous cows: 3 DOT: ODM 1% (95% confidence interval: 0-10%) vs. TDM 43% (30-58%), 15 DOT ODM 0% (0-0.2%) vs. TDM 22% (13-36%); multiparous cows: 3 DOT: ODM 33% (24-44%) vs. TDM 59% (48-69%), 15 DOT ODM 20.9% (13-31%) vs. TDM 64% (53-74%)]. The proportion of ODM cows that required additional treatments of PG were substantially lower than the TDM group (ODM: 39%; TDM: 64%) than the TDM cows during the initial 21-d period. However, during the 2-wk treatment period, cows in the ODM group produced 26% less milk and 25% less energy-corrected milk than the TDM cows. During wk 3 to 15, when all cows were milked twice daily, ODM cows produced less milk (-14%) and energy-corrected milk (-12%) compared with the TDM group. Milk protein percentage was greater, and milk fat percentage and linear score tended to be greater in the ODM group over 15 wk. In conclusion, a 2-wk reduction of MF in ketotic cows from twice to once daily with treatment with PG resolved ketosis and decreased blood BHB concentrations more effectively than treating TDM cows with PG alone. However, the 2-wk MF reduction had immediate and long-term (up to 13 wk after cessation of MF reduction) negative effects on milk production., (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/).)

The objective of this study was to investigate whether health, survival, and performance of dairy heifers from birth through first lactation are associated with parity and health status of their dams. Holstein heifers (n = 1,811) derived from artificial insemination were categorized as (1) daughters of primiparous cows that, consequently, were nonlactating heifers during gestation (Prim-NoL; n = 787); (2) daughters of multiparous cows that did not have any clinical diseases in the previous lactation (Mult-NoCD; n = 638); and (3) daughters of multiparous cows that had at least one clinical disease in the previous lactation (Mult-CD; n = 386). Clinical diseases of the multiparous dams included retained placenta, metritis, mastitis, lameness, and digestive and respiratory problems. Data collected for evaluation of daughters included genotypic and phenotypic characteristics at birth, morbidity, reproductive performance, and culling from birth through 305 d in milk of first lactation. Orthogonal contrasts were used to evaluate the effect of the parity of the dam (Prim-NoL vs. Mult-NoCD + Mult-CD) and the effect of clinical disease occurrence in the previous lactation among multiparous dams (Mult-NoCD vs. Mult-CD). Compared with daughters of multiparous cows, daughters of Prim-NoL were lighter at birth (36 vs. 41 kg), had greater genetic merit for production traits (e.g., genomic estimated breeding value for milk yield: 875 vs. 746 kg), were less likely to leave the herd (17 vs. 28%) and to lose pregnancy as a heifer (9 vs. 14%), calved earlier (703 vs. 711 d old), were less likely to have clinical diseases as a first lactation cow (30 vs. 37%), and had reduced performance in the first lactation when considering their genetic merit (e.g., 305-d yield of energy-corrected milk: 11,270 vs. 11,539 kg). Compared with daughters of Mult-NoCD, daughters of Mult-CD were less likely to have digestive problems as a heifer (17 vs. 27%) and clinical disease as a first lactation cow (32 vs. 42%), but were also more likely to leave the herd as a heifer (32 vs. 25%) even though genetic merit for production traits were similar (e.g., genomic estimated breeding value for milk: 744 vs. 749 kg). In conclusion, both parity and health status of the dam in the previous lactation were associated with morbidity, survival, and performance of their daughters from birth through 305 d in milk of the first lactation and might represent factors affecting developmental programming of dairy heifers in utero., (Copyright © 2020 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Six classical growth functions (monomolecular, Schumacher, Gompertz, logistic, Richards, and Morgan) were fitted to individual and average (by parity) cumulative milk production curves of Canadian Holstein dairy cows. The data analyzed consisted of approximately 91,000 daily milk yield records corresponding to 122 first, 99 second, and 92 third parity individual lactation curves. The functions were fitted using nonlinear regression procedures, and their performance was assessed using goodness-of-fit statistics (coefficient of determination, residual mean squares, Akaike information criterion, and the correlation and concordance coefficients between observed and adjusted milk yields at several days in milk). Overall, all the growth functions evaluated showed an acceptable fit to the cumulative milk production curves, with the Richards equation ranking first (smallest Akaike information criterion) followed by the Morgan equation. Differences among the functions in their goodness-of-fit were enlarged when fitted to average curves by parity, where the sigmoidal functions with a variable point of inflection (Richards and Morgan) outperformed the other 4 equations. All the functions provided satisfactory predictions of milk yield (calculated from the first derivative of the functions) at different lactation stages, from early to late lactation. The Richards and Morgan equations provided the most accurate estimates of peak yield and total milk production per 305-d lactation, whereas the least accurate estimates were obtained with the logistic equation. In conclusion, classical growth functions (especially sigmoidal functions with a variable point of inflection) proved to be feasible alternatives to fit cumulative milk production curves of dairy cows, resulting in suitable statistical performance and accurate estimates of lactation traits., (Copyright © 2015 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The objective of the study was to determine the effect of active dry Saccharomyces cerevisiae (ADSC) supplementation on dry matter intake, milk yield, milk components, ruminal pH, and microbial community during a dietary regimen that leads to subacute ruminal acidosis (SARA). Sixteen multiparous, rumen-cannulated lactating Holstein cows were randomly assigned to 1 of 2 dietary treatments that included ADSC (Biomate; AB Vista, Marlborough, UK; 8 × 10(10) cfu/head per day) or control. During wk 1 to 6, all cows received a high-forage (HF) diet (77:23, forage:concentrate). Cows were then abruptly switched during wk 7 to a high-grain (HG) diet (49:51, forage:concentrate) and remained on the HG until the end of wk 10. Feed intake and milk yields were recorded daily. Ruminal pH was recorded continuously using an indwelling system for 1 to 2 d per week during the pre-experimental phase, and wk 6, 7, and 10. Ruminal digesta samples were collected at the end of the experiment and analyzed for relative change in microbial communities using real-time quantitative PCR. Cows were considered to have SARA if the duration below pH 5.6 was ≥300 min/d. Ruminal pH during wk 6 (HF plateau) was not different across treatments (15 ± 46 min/d at pH <5.6). The dietary regimen successfully induced SARA during wk 7 (transition from HF to HG diet), and ruminal pH (551 ± 46 min/d at pH <5.6) was not different across treatments. However, cows receiving ADSC had an improved ruminal pH (122 ± 57 vs. 321 ± 53 min/d at pH <5.6) during wk 10 (HG plateau) compared with control. Additionally, cows receiving ADSC had a better dry matter intake (23.3 ± 0.66 vs. 21.6 ± 0.61 kg/d) and 4% fat-corrected milk yield (29.6 ± 1.2 vs. 26.5 ± 1.2 kg/d) than control cows during the HG phase (wk 8 to 10). During HG feeding, cows receiving ADSC had greater total volatile fatty acid and propionate concentrations (175 ± 7.5 vs. 154 ± 7.5 and 117 ± 6.1 vs. 94 ± 5.7 mM for ADSC and control, respectively) and lower acetate:propionate ratio (0.26 ± 0.5 vs. 0.36 ± 0.05 for ADSC and control, respectively). Microbial analyses conducted on samples collected during wk 10 showed that cows supplemented with S. cerevisiae had a 9-fold, 2-fold, 6-fold, 1.3-fold, and 8-fold increase in S. cerevisiae, Fibrobacter succinogenes, Anaerovibrio lipolytica, Ruminococcus albus, and anaerobic fungi, respectively, which suggested an increase in cellulolytic microbes within the rumen. Cows supplemented with ADSC had 2.2-fold reduction in Prevotella albensis, which is a gram-negative bacterium predominant during SARA. Prevotella spp. are suggested to be an important source of lipopolysaccharide responsible for inflammation within the rumen. Cows supplemented with ADSC had a 2.3-fold increase in Streptococcus bovis and a 12-fold reduction in Megasphaera elsdenii. The reduction in M. elsdenii may reflect lower concentration of lactic acid within the rumen for ADSC cows. In conclusion, ADSC supplementation to dairy cows was demonstrated to alleviate the condition of SARA caused by abrupt dietary changes from HF to HG, and can potentially improve rumen function, as indicated by greater numbers of cellulolytic microorganisms within the rumen., (Copyright © 2014 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The objective of this study was to determine the effect of feed delivery frequency on the behavioral patterns and productivity of lactating dairy cows. Twelve freestall-housed, lactating Holstein dairy cows, including 6 primiparous (PP) and 6 multiparous (MP), milked 3 ×/d (at 1400, 2200, and 0600 h), were exposed to each of 3 treatments (over 21-d periods) in a replicated Latin square design. Treatments included feed delivery frequency of (1) 1 ×/d (at 1400 h), (2) 2 ×/d (at 1400 and 2200 h), and (3) 3 ×/d (at 1400, 2200, and 0600 h). Milk production as well as feeding, lying, and rumination behaviors were electronically monitored for each animal for the last 7d of each treatment period. Milk samples were collected for the last 3d of each period for milk component analysis. Dry matter intake (DMI) varied with feed delivery frequency, with greatest DMI observed in cows fed 3 ×/d (27.8 kg/d) compared with those fed 2 ×/d (27.0 kg/d) or 1 ×/d (27.4 kg/d). Treatment had no effect on milk yield (41.3 kg/d) or efficiency of production (1.54 kg of milk/kg of DMI). Cows that did not receive delivery of feed following the 2200 h milking (treatment 1) and 0600 h milking (treatments 1 and 2) had lower DMI during the first hour after milking than those that received feed at all milkings (treatment 3). Total feeding time and meal frequency, size, and duration did not vary by treatment, but PP cows consumed smaller meals at a slower rate, resulting in lower DMI compared with MP cows. Primiparous cows consumed 50.1% and 26.1% less dry matter than MP cows during the first meal following the first and second milkings, respectively. Lying time did not vary by treatment, but PP cows spent more time lying (10.3 vs. 8.3h/d) than MP cows. Under 3 ×/d milking schedules, greater feed delivery frequency resulted in greater DMI as a function of increased DMI following the return from milking and the delivery of feed., (Copyright © 2014 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The challenges associated with group-housed dairy cows include within-herd variability in nutrient consumption and milk production, which may be related to feeding management. The objective of this observational study was to examine the association of herd-level feeding management factors, feed sorting, and milk production. Twenty-two freestall herds with an average lactating herd size of 162±118 cows, feeding total mixed rations, were each studied for 7 consecutive days in summer and winter. In cases of multiple feeding groups within a herd, the highest producing group of cows with an even distribution of days in milk and parity was selected for this study. The average group size studied was 83±31 cows. The average study group consisted of cows 187±47 days in milk, with a parity of 2.3±0.6, consuming 24.3±2.6kg of dry matter, with an average group-level yield of 34.3±6kg of milk/d, 3.7±0.3% milk fat, and 3.2±0.18% milk protein. Milk production parameters, including yield, fat, and protein, were recorded through regular Dairy Herd Improvement milk testing. A survey of feeding management practices and barn characteristics was administered on each farm. The amounts of feed offered and refused were recorded and sampled daily to assess dry matter intake (DMI) and particle size distribution. Feeding twice per day compared with once per day was associated with an average increase of 1.42kg of DMI, 2.0kg of milk yield, and less sorting against long ration particles (>19mm). Every 2% group-level selective refusal (sorting) of long particles was associated with 1kg/d of reduction in milk yield. A 10cm/cow increase in feed bunk space was associated with a 0.06-percentage-point increase in group-average milk fat and a 13% decrease in group-average somatic cell count. These results support that herd-level management practices to promote feed access, such as increased feeding frequency and bunk space, may improve DMI and promote more balanced nutrient intake and greater milk production., (Copyright © 2013 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The objective of this study was to determine the effect of milking frequency on the behavioral patterns and productivity of lactating dairy cows. Twelve freestall-housed, lactating Holstein dairy cows (7 primiparous and 5 multiparous) were exposed to each of 2 treatments (over 21-d periods) in a replicated crossover design. Treatments were milking frequency of 2× /d (at 0600 and 1800 h) or 3× /d (at 0600, 1400, and 2200 h). Milk production, feeding, lying, and rumination behavior were monitored for each animal for the last 7d of each treatment period. Milk samples were collected for the last 3d of each period for milk component analysis. The results indicated that cows milked 3× /d produced 2.9 kg/d more milk than those milked 2× /d. Primiparous cows consumed 3.9 kg/d less dry matter (DM) than did multiparous cows. The extra time (14.6 min/d) required for milking 3× /d altered the distribution of cow behavioral activity throughout the day. Although this did not affect total daily lying or rumination time, we observed a tendency for cows milked 2× /d to spend less time (224.6 vs. 237.5 min/d) feeding and, thus, those cows tended to consume their feed at a faster rate (0.13 vs. 0.12 kg of DM/min) than cows milked 3× /d. For multiparous cows, the increase in feeding activity was facilitated through having longer (40.1 vs. 36.8 min/meal) and numerically larger meals (4.8 vs. 4.6 kg of DM/meal) when milked 3× /d. Alternatively, primiparous cows consumed smaller (2.9 vs. 3.2 kg of DM/meal) and more frequent meals (9.1 vs. 7.7 meals/d) throughout the day when milked 3× /d, resulting in a tendency for greater DM intake (24.7 vs. 23.6 kg/d) compared with primiparous cows milked 2× /d. These results indicate that under 3× /d milking schedules, primiparous cows will positively adjust their feeding behavior to achieve similar production increases as multiparous cows. In summary, milking 3× /d can be used to improve production; however, greater milking frequency elicits varying effects on the behavior of primiparous and multiparous cows, suggesting that grouping and management of cows based on parity may be beneficial., (Copyright © 2013 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

In recent years, livestock producers have been supplementing animal diets with fish meal (FM) to produce value-added products for health conscious consumers. As components of FM have unique neuroendocrine-immunomodulatory properties, we hypothesize that livestock producers may be influencing the overall health of their animals by supplementing diets with FM. In this study, 40 pregnant ewes were supplemented with rumen protected (RP) soybean meal (SBM: control diet) or RP FM, commencing gestation day 100 (gd100), in order to evaluate the impact of FM supplementation on the innate and acquired immune response and neuroendocrine response of sheep during pregnancy and lactation. On gd135, half the ewes from each diet (n = 10 FM, n = 10 SBM) were challenged iv with lipopolysaccharide (LPS) to simulate a systemic bacterial infection and the febrile, respiratory and neuroendocrine responses were monitored over time; the other half (n = 10 FM, n = 10 SBM) of the ewes received a saline injection as control. On lactation day 20 (ld20), all ewes (n = 20 FM, n = 20 SBM) were sensitized with hen egg white lysozyme (HEWL) and the serum haptoglobin (Hp) response was measured over time. The cutaneous hypersensitivity response (CHR) to HEWL challenge was measured on ld30 (n = 20 FM, n = 20 SBM), and blood samples were collected over time to measure the primary and secondary immunoglobulin G (IgG) response to HEWL. There was an attenuated trend in the LPS-induced febrile response by the FM treatment when compared with the SBM treatment (P = 0.06), as was also true for the respiratory response (P = 0.07), but significant differences in neuroendocrine function (serum cortisol and plasma ACTH) were not observed between treatments. Basal Hp levels were significantly lower in the FM supplemented ewes when compared with the SBM supplemented ewes (P < 0.01), and the Hp response to HEWL sensitization differed significantly over time between treatments (P < 0.01). The CHR to HEWL was also significantly attenuated in the FM treatment compared with the SBM (P < 0.01); however, treatment differences in the primary and secondary IgG responses to HEWL were not observed. These results indicate that FM supplementation differentially affects the innate and acquired immune responses in pregnant and lactating sheep compared with a typical SBM diet of commercial flocks. The long-term implications of this immunomodulation warrant further investigation.

Data from 1,010 lactating lactating, predominately component-fed Holstein cattle from 25 predominately tie-stall dairy farms in southwest Ontario were used to identify objective thresholds for defining hyperketonemia in lactating dairy cattle based on negative impacts on cow health, milk production, or both. Serum samples obtained during wk 1 and 2 postpartum and analyzed for beta-hydroxybutyrate (BHBA) concentrations that were used in analysis. Data were time-ordered so that the serum samples were obtained at least 1 d before the disease or milk recording events. Serum BHBA cutpoints were constructed at 200 micromol/L intervals between 600 and 2,000 micromol/L. Critical cutpoints for the health analysis were determined based on the threshold having the greatest sum of sensitivity and specificity for predicting the disease occurrence. For the production outcomes, models for first test day milk yield, milk fat, and milk protein percentage were constructed including covariates of parity, precalving body condition score, season of calving, test day linear score, and the random effect of herd. Each cutpoint was tested in these models to determine the threshold with the greatest impact and least risk of a type 1 error. Serum BHBA concentrations at or above 1,200 micromol/L in the first week following calving were associated with increased risks of subsequent displaced abomasum [odds ratio (OR) = 2.60] and metritis (OR = 3.35), whereas the critical threshold of BHBA in wk 2 postpartum on the risk of abomasal displacement was >or=1,800 micromol/L (OR = 6.22). The best threshold for predicting subsequent risk of clinical ketosis from serum obtained during wk 1 and wk 2 postpartum was 1,400 micromol/L of BHBA (OR = 4.25 and 5.98, respectively). There was no association between clinical mastitis and elevated serum BHBA in wk 1 or 2 postpartum, and there was no association between wk 2 BHBA and risk of metritis. Greater serum BHBA measured during the first and second week postcalving were associated with less milk yield, greater milk fat percentage, and less milk protein percentage on the first Dairy Herd Improvement test day of lactation. Impacts on first Dairy Herd Improvement test milk yield began at BHBA >or=1,200 micromol/L for wk 1 samples and >or=1,400 micromol/L for wk 2 samples. The greatest impact on yield occurred at 1,400 micromol/L (-1.88 kg/d) and 2,000 micromol/L (-3.3 kg/d) for sera from the first and second week postcalving, respectively. Hyperketonemia can be defined at 1,400 micromol/L of BHBA and in the first 2 wk postpartum increases disease risk and results in substantial loss of milk yield in early lactation.

The objective of this study was to determine the long-term effects of feeding monensin on milk fatty acid (FA) profile in lactating dairy cows. Twenty-four lactating Holstein dairy cows (1.46 +/- 0.17 parity; 620 +/- 5.9 kg of live weight; 92.5 +/- 2.62 d in milk) housed in a tie-stall facility were used in the study. The study was conducted as paired comparisons in a completely randomized block design with repeated measurements in a color-coded, double blind experiment. The cows were paired by parity and days in milk and allocated to 1 of 2 treatments: 1) the regular milking cow total mixed ration (TMR) with a forage-to-concentrate ratio of 60:40 (control TMR; placebo premix) vs. a medicated TMR [monensin TMR; regular TMR + 24 mg of Rumensin Premix per kg of dry matter (DM)] fed ad libitum. The animals were fed and milked twice daily (feeding at 0830 and 1300 h; milking at 0500 and 1500 h). Milk samples were collected before the introduction of treatments and monthly thereafter for 6 mo and analyzed for FA composition. Monensin reduced the percentage of the short-and medium-chain saturated FA 7:0, 9:0, 15:0, and 16:0 in milk fat by 26, 35, 19, and 6%, respectively, compared with the control group. Monensin increased the percentage of the long-chain saturated FA in milk fat by 9%, total monounsaturated FA by 5%, total n-6 polyunsaturated FA (PUFA) by 19%, total n-3 PUFA by 16%, total cis-18:1 by 7%, and total conjugated linoleic acid (CLA) by 43% compared with the control group. Monensin increased the percentage of docosahexaenoic acid (22:6n-3), docosapentaenoic acid (22:5n-3), and cis-9, trans-11 CLA in milk fat by 19, 13, and 43%, respectively, compared with the control. These results suggest that monensin was at least partly effective in inhibiting the biohydrogenation of unsaturated FA in the rumen and consequently increased the percentage of n-6 and n-3 PUFA and CLA in milk, thus enhancing the nutritional properties of milk with regard to human health.

Effects of prepartum administration of a monensin controlled release capsule (CRC) on rumen pH, dry matter intake, and milk production during the transition period and early lactation were determined in 16 multiparous Holstein cows. Cows were divided into blocks of 2 depending on calving date. Cows were fed either a close-up dry cow or a lactating cow total mixed ration ad libitum. Rumen pH was monitored continuously using indwelling probes. Monensin did not affect average daily rumen pH, time below pH 6, time below pH 5.6, area below pH 6, and area below pH 5.6 throughout the experiment. Average daily pH, time below pH 6, and time below pH 5.6 before calving were 6.62, 65.6 min/d, and 17.6 min/d, respectively, and did not differ among the weeks before calving. Average daily pH, time below pH 6, and time below pH 5.6 were 6.19, 443.3 min/d, and 115.5 min/d, respectively, during the first week after calving, and were 6.36, 204.3 min/d, and 52.4 min/d, respectively, during the sixth week after calving. In the weeks after calving, average daily pH showed a quadratic increase, time below pH 6 showed a quadratic decrease, and time below pH 5.6 showed a linear decrease. Monensin did not affect dry matter intake and daily yields of milk, milk fat, and milk protein. Results suggest that prepartum administration of a monensin CRC did not increase rumen pH in multiparous cows fed the experimental diets during the transition period and early lactation.

The effect of ruminally protected Met (RPM) on splanchnic metabolism was measured in 3 primiparous and 3 multiparous Holstein cows. Doses of RPM (0, 36, and 72 g/d) were tested in a replicated 3 x 3 Latin square design, over 3 consecutive 14-d experimental periods. A mixed ration was fed in 12 equal meals per d (average dry matter intake: 17.5 +/- 0.08 kg/d). Indwelling catheters were surgically implanted in the mesenteric artery and the portal and hepatic veins for blood collection, as well as in 2 distal branches of the mesenteric vein for infusion of p-aminohippurate to determine blood flow. On d 14 of each period, a temporary catheter was inserted into a mammary vein and 6 hourly blood samples were collected to determine plasma concentrations of metabolites, hormones, and their respective fluxes across the splanchnic bed and mammary glands. Yields of milk (32.8, 32.0, and 32.9 +/- 0.92 kg/d) and protein (1,028, 1,053, and 1,075 +/- 28.7 g/d) were unaffected by level of RPM. However, the true protein content in milk from primiparous cows increased linearly (2.92, 3.09, and 3.34 +/- 0.077%). The addition of RPM linearly increased the net flux of Met across the portal-drained viscera, which resulted in increased arterial Met concentrations (25, 29, and 40 +/- 1.1 microM). Although it had no significant effect on net portal and hepatic fluxes of other essential amino acids, RPM resulted in a linear increase in the total splanchnic output of Ile, Leu, Phe, and Thr. These results suggest that feeding RPM triggered a homeostatic response resulting in less utilization of certain essential amino acids through the gastrointestinal tract and liver. Net mammary uptake of Met did not change with the addition of RPM. However, mammary extraction of Met decreased in a linear fashion in response to increased arterial inflow.

Effects of prepartum administration of a monensin controlled release capsule (CRC) and stage of lactation on variation of blood metabolites within 24 h were determined in 16 dairy cows. Cows were fed a total mixed ration ad libitum twice daily at 0700 and 1300 h. At calving, cows were switched from a close-up dry cow diet to a lactating cow diet. Cows were blood sampled every 3 h for 24 h at 3 stages of lactation, including 1 wk before calving (wk -1), 1 wk after calving (wk 1), and 6 wk after calving (wk 6). Serum concentrations of glucose, beta-hydroxybutyrate (BHBA), nonesterified fatty acids (NEFA), and urea exhibited significant variation within 24 h. Glucose and NEFA were, respectively, 0.09 and 0.08 mM lower between 1030 and 2230 h than between 2230 and 1030 h. beta-Hydroxybutyrate and urea were, respectively, 95.1 and 0.49 mM higher between 1030 and 2230 h than between 2230 and 1030 h. Monensin did not significantly affect glucose, NEFA, and urea in this study. Monensin reduced BHBA at wk 1, but not at wk -1 or wk 6. Glucose was lower and BHBA and NEFA were higher at wk 1 compared with wk -1 and wk 6. Urea was higher at wk 6 compared with wk -1. The variation within 24 h of glucose, BHBA, and NEFA were not affected by monensin and stage of lactation. Diurnal variation of urea was affected by stage of lactation, but not by monensin.

Subacute rumen acidosis is thought to be a common condition in early lactating dairy cattle; however, diagnosis is difficult. There are currently only two techniques available for measuring rumen pH under field conditions: rumenocentesis and oral stomach tube. Sixteen rumen-fistulated cows were sampled in four sites of the rumen (cranial-ventral, caudal-ventral, central, and cranial-dorsal) with a rumen cannula. Rumen pH results were compared to those obtained at the same time with rumenocentesis and with an oro-ruminal (Geishauser) probe. Rumen fluid was obtained between 6 and 12 wk of lactation. Samples were analyzed for pH, lactate, bicarbonate, sodium, potassium, and chloride. Rumen pH results were also compared to those obtained from 24-h continuous rumen pH measurement using indwelling rumen pH probes. Oro-ruminal probe samples had the highest pH values and the highest bicarbonate concentrations. Rumenocentesis samples had the lowest pH values and the lowest bicarbonate concentrations. Small differences in electrolyte concentrations were noted among rumen fluid collection techniques in the different rumen sites. The highest correlations of rumen pH were obtained between rumenocentesis and rumen cannulation (cranial-ventral), and between rumen cannulation (cranial-ventral) and the 24-h indwelling pH meter. Compared with samples obtained from the cranial-ventral rumen, rumenocentesis was more sensitive than the oro-ruminal probe in the measurement of low rumen pH; both techniques were moderately specific. The most accurate field technique was rumenocentesis. Improved field techniques are required for better on-farm diagnosis of subacute rumen acidosis.

The effect of inducing subacute ruminal acidosis (SARA) on the free-choice intake of sodium bicarbonate (SB) was investigated in four midlactation Holstein cows in a switchover experiment with four 1-wk periods. The SARA was induced by replacing 25% of the ad libitum intake of total mixed ration (TMR) with pellets containing 50% ground wheat and 50% ground barley and restricting access to TMR from 0700 to 1700 h. Control consisted of feeding TMR ad libitum. Powdered SB was provided for ad libitum consumption. Rumen pH was measured continuously using indwelling pH probes. Induction of SARA reduced (P < 0.05) the average daily rumen pH from 6.08 to 5.87, increased (P < 0.05) the average duration of rumen pH below 6 from 547 min x d(-1) to 916 min x d(-1), and increased (P < 0.05) the average duration of rumen pH below 5.6 from 132 min x d(-1) to 397 min x d(-1) (P < 0.05) but did not significantly affect SB intake. Average intake of SB was 26.8 g x d(-1) during SARA and 34.5 g x d(-1) during control. These low SB intakes must not have substantially affected rumen pH. Sodium bicarbonate intake differed significantly (P < 0.05) between cows. These data indicate that cows did not select SB in order to attenuate SARA.

This experiment determined the effects of dietary protein solubility on amount, form, and route of nitrogen loss in lactating Holstein dairy cows, and the ability of the Cornell Net Carbohydrate and Protein System (CNCPS) to accurately predict rumen microbial yield, serum urea N (SUN), milk urea N (MUN), and fecal N. Eighteen multiparous Holstein cows were assigned randomly to one of three dietary treatments that were similar in crude protein (17.7%) content but differed in their content of soluble intake protein (SIP). Dietary contents of SIP, as % of total CP were 30, 36, and 48%. The experimental period was 21 d, and total N balance collections were done during the last 5 d. As dietary content of SIP increased, excretion of urinary N increased quadratically, and it was the primary route of N excretion. Urinary excretion of purine derivatives (PD) responded quadratically as dietary SIP content increased. The CNCPS predicted a quadratic decrease in total metabolizable protein (MP) supply. No effect of dietary content of SIP was detected on MUN and SUN. The CNCPS predicted a quadratic decrease in SUN and MUN as dietary SIP increased. Results from this study indicated that changing the dietary content of SIP altered routes of N excretion in dairy cows, but had no effect on total N balance. The CNCPS did not adequately predict changes in SUN and MUN for cows fed diets varying in SIP.

To evaluate a close mammary infusion technique for the study of milk protein responses to blood amino acid profile, five early-lactation, multiparous Holstein cows were surgically fitted with catheters in both external iliac arteries. Animals were infused into one arterial catheter with five different solutions on 5 consecutive days in a Latin square design. Infusions began at 0800 h and continued until 1800 h. The five infusates were a 3% saline control, 15 g/h of complete amino acid mix, 15 g/h of imbalanced amino acid mix (minus His), 30 g/h of complete amino acid mix, and 30 g/h of imbalanced amino acid mix (minus His). Cows were fed a total mixed ration twice daily containing 16% crude protein and 1.7 Mcal/kg of net energy for lactation. Infusion of the complete amino acid mix elevated amino acid concentrations in arterial plasma two- to threefold but caused only a small dose-dependent increase in milk protein content and yield. Fat percentage in milk was decreased from 4.08 to 3.35% by the complete amino acid infusions so that the protein:fat ratio climbed from 0.76 on the control to 0.99 with 30 g/h of amino acid. Removal of His from the infusate caused plasma His concentrations to drop but had no effect on any other circulating amino acids. Milk composition was restored to control levels by removal of the single amino acid. A short-term circulating amino acid imbalance depresses milk protein percentage and increases milk fat content in dairy cows.

Dry cows and pregnant heifers from 25 farms near Guelph, Ontario, Canada were enrolled in a large double-blind, randomized clinical trial that was designed to evaluate the impact of monensin on energy metabolism, health, and production. A total of 503 cows was given monensin in controlled-release capsules, and 507 were administered placebo capsules 3 wk prior to the expected calving date. The effects of treatment on milk production and milk components at the first three Dairy Herd Improvement (DHI) tests were evaluated using repeated measures analysis of variance. Treatment with monensin increased milk production, but this effect was dependent on body condition score prior to calving. Cows that were classified as thin (score of < or = 3.0) did not have increased production in response to monensin treatment. Cows with fair body condition (score of 3.25 to 3.75) produced significantly more milk at the second DHI test (+0.85 kg), but cows that were fat (score of > or = 4.0) produced significantly more milk than did controls for all three DHI tests (+1.25 kg) in early lactation. Monensin significantly increased projected 305-d milk production in cows from herds at increased risk of ketosis. Treatment with monensin had no significant effect on either milk fat percentage or milk protein percentage.

A mathematical model is used to describe uptake by a countertransport system and subsequent flow of three amino acids (AA), Phe, Val, and Met, from arterial blood to milk protein in the mammary gland of a lactating cow. The model suggests that total uptake of all AA is higher than net uptake and that a large proportion of the incoming AA is released from the cell directly back to blood. The model is used to predict which of the three AA is limiting the rate of milk protein synthesis and the response to increased arterial concentration of the first-limiting AA. Simulations are performed to predict possible outcomes of several experimental protocols to AA infusion, which might be used to test in vivo the responsiveness of the bovine mammary gland to an altered arterial concentration of AA. Of the three AA considered, arterial Met concentration appears to be first-limiting. The infusion profile that gives the greatest response in milk protein synthesis rate alters the arterial profile of AA such that it is identical to that of proteins originating in the mammary gland. Model construction can be simplified by acknowledging normal biological constraints.

Anti-idiotypic antibodies produced in lactating cows by immunization with rabbit antibodies raised against bovine somatotropin (bST) were evaluated for bST-like immunoactive and biological activities. Twenty New Zealand White rabbits were immunized against bST. Serum was purified using protein A-Sepharose CL-4B and bST-Sepharose 4B affinity chromatography to yield specific anti-bST immunoglobulin G (IgG). Twenty-four lactating cows were allocated to a randomized complete block design and were immunized with either: (1) rabbit anti-bST (n = 12) or (2) non-specific rabbit IgG (n = 12, control). Cows were immunized starting at day 68 of lactation with 800 micrograms antigen emulsified with Freund's complete adjuvant and 1 mg Quil A administered by i.m. injections. Repeated immunizations of 800 micrograms antigen in Freund's incomplete adjuvant and 1 mg Quil A followed after 3 weeks and then every 5 weeks throughout lactation. Serum samples were collected twice weekly and were analysed for anti-rabbit IgG titre and immunoactive bST concentration by radioimmunoassay. All cows developed antibodies against rabbit IgG by the second and third immunizations. With rising titres, immunoactive bST concentrations increased in cows treated with anti-bST following each of the six repeated immunizations to 4.7 +/- 3.3, 10.0 +/- 4.2, 12.0 +/- 4.8, 17.3 +/- 6.7, 24.0 +/- 10.0 and 36.3 +/- 20.4 ng/ml (mean +/- S.E.M.) compared with controls (0.81 +/- 0.09 ng/ml, overall mean +/- S.E.M.). To assess the biological activity of these bST anti-idiotypic antibodies, milk yield and serum insulin-like growth factor-I (IGF-I) concentrations were analysed in all cows and a subset of six cows per treatment respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Twenty-five primigravid ewes were used to investigate the effect of bST, between 97 and 124 d of gestation, on mammogenesis and subsequent milk production. Five ewes (reference group) were slaughtered at 96 d of gestation, and the remaining ewes were injected daily with saline (control group: n = 10) or .1 mg/kg of BW of bST (bST group: n = 10). Following bST treatment, 5 control and 5 bST group ewes were slaughtered (slaughter group). The remaining ewes were slaughtered after lambing and being milked for 8 wk (production group). Weekly blood samples were obtained from both slaughter and production group ewes. Slaughter group ewes were also subjected to 8-h serial blood sampling at 98 d (period 1) and 123 d (period 2) of gestation. Milk production was 42% higher in ewes treated prepartum with bST than in those treated with saline. Results suggest that the increase in milk was due to an increase in mammary parenchymal cell number rather than to an increase in cellular activity. The high rate of [3H]thymidine incorporation into parenchymal tissue in reference group ewes suggests that the increase in parenchyma during the second trimester of gestation is due to cellular hyperplasia but that cellular hypertrophy may be more important during the last trimester. Plasma IGF-I concentrations were significantly higher during bST treatment and remained elevated between daily injections; the increase was greatest in period 2.

Seventy-four Holstein cows (26 primiparous) were utilized to compare the efficacy and safety of sustained-release versus daily injectable formulations of recombinant bST. Twenty-four control cows were injected biweekly with oil microsphere; 25 cows were injected biweekly with 350 mg of bST microsphere; and 25 cows were injected daily with 10.3 mg of bST. Injections were initiated between wk 4 and 5 of lactation and continued for 280 d. Administration of bST caused a moderate increase in milk and FCM production and improved the efficiency of feed and energy conversions. Most health-related and reproduction-related variables did not differ among treatment groups. However, incidence of teat and udder disorders and feet and leg problems tended to be higher during the 40-wk injection period for the bST-treated cows than for the control cows. Incidence of GnRH therapy and number of days to first service were higher for daily bST-treated cows than for controls. No differences existed between sustained-release and daily bST-treated cows for any parameters monitored.

Thirteen (control) cows were injected daily with saline and 22 with bST (12 at 10.3 mg/d and 10 at 20.6 mg/d) through wk 5 to 42 of lactation. Nine of the treated cows had received bST in the previous lactation, and 7 cows received bST in the previous two lactations. All control cows and 6 treated cows had not previously received bST. Treatment with bST caused substantial increases in milk production, feed intake, and efficiency of feed conversion in the current lactation, which is consistent with previous trials. Increases in feed intake were established fully within 9 wk of starting bST administration, somewhat earlier than usually reported. Treatment with bST in one or two previous lactations caused a statistically significant 14% reduction in production and 8% reduction in efficiency of feed conversion during the first 9 wk of bST treatment in the current lactation; reductions observed later in lactation were not statistically significant. Differences for other traits were not statistically significant. In combination with earlier trials, these results suggest that, although bST has beneficial effects on production and efficiency traits, these benefits may be considerably lower in the second and subsequent lactations of bST use. However, carry-over effects on cows not receiving bST in the current lactation were not explored in this trial.

Evidence was sought for an interaction between both phenotypic and genetic production potential and response of milk production to administration of bST in three trials of 38, 43, and 35 cows. In each trial, bST was administered in doses of 0, 10.3, 20.6, and, in trial 1 only, 41.2 mg/d for 38 wk from wk 4 of lactation. Data were analyzed for each experiment separately and combined across experiments. Analyses included separate regressions for treated and untreated animals for milk production during the production period on pretreatment production and estimated breeding value for milk production. Breeding value was estimated as the sire's estimated transmitting ability plus one-half of the maternal grandsire's estimated transmitting ability. With the exception of regression on estimated breeding value in trial 1 and in combined data, differences between treated and untreated animals in the regression of milk production on pretreatment milk production or on estimates of breeding value were not statistically significant. However, regressions on pretreatment production were substantially lower for treated than for untreated animals in each of the three trials. Regressions on breeding value estimated from sire and maternal grandsire estimated transmitting abilities were substantially, but not significantly, lower for untreated than for treated animals in all three trials. The results suggest that cows with high production potential for nongenetic reasons may show diminished response to bST, whereas cows with genetically high production potential show enhanced response. However, borderline statistical significance argues for considerable further examination before drawing firm conclusions.

Thirty-seven primigravid Holstein heifers (600.7 +/- 9.4 kg) were used to determine the effect of recombinant bST, administered during the last trimester of gestation, on growth and subsequent 270-d milk yield. Treatments consisted of daily subcutaneous injections of saline or of 20 or 40 mg of recombinant bST. Four weeks before expected date of parturition, 8 heifers (3 receiving saline, 3 receiving 20 mg of bST, and 2 receiving 40 mg of bST) were fitted with jugular catheters, and blood plasma bST and insulin-like growth factor-I concentrations were determined in samples collected during a 9-h period. Feed efficiency (DMI/gain) was improved in heifers treated with 20 mg of bST, but DMI was not affected by treatment. Average daily gain was increased in heifers treated with 20 mg of bST, but not in those treated with 40 mg of bST. Fat-uncorrected milk yield following prepartum bST treatment was 19% higher in heifers treated with 20 mg of bST, but the 40-mg dose of bST did not increase milk yield. Percentage of milk fat was lower in heifers treated with 20 mg of bST prepartum, but daily milk fat yields did not differ among groups. Solids-not-fat yield was highest in the group treated previously with 20 mg of bST. The higher milk yield of these heifers became significant (P less than .05) only after 90 d of lactation. Plasma bST and insulin-like growth factor-I concentrations were both elevated in bST-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Our objectives were to determine the effects of exogenous bovine somatotropin on peripheral blood lymphocyte responsiveness to mitogen and on concentrations of serum insulin-like growth factor-I and to determine whether a statistical relationship exists between these two variables. The cows on trial were treated with 0, 10.3, or 20.6 mg/d somatotropin, starting between wk 4 and 5 of lactation and continuing for 266 consecutive d. Lymphocyte proliferation (counts per minute) and concentration of insulin-like growth factor-I (nanograms per milliliter) were recorded from blood sampled at wk 3, 10, 26, 35, and 46 of lactation. The results showed that lymphocytes from the blood of treated cows responded to mitogen with higher proliferative responsiveness than cells from control cows, but that this effect required long-term treatment and adequate mitogen concentrations to be detected. The blood of treated cows also had elevated concentrations of insulin-like growth factor-I relative to that of control cows, but these were not statistically associated with the proliferative responsiveness of the peripheral blood lymphocytes to mitogen. Our results suggest that somatotropin has a role in the immune system of cows, but its mode of action and target tissues must be determined. Bovine somatotropin, injected at doses that increase milk yield, can augment cow immunity as judged by the proliferative responsiveness of peripheral blood lymphocytes in culture.

Consistent with the increased demand for nutrients imposed by lactation and growth, those tissues directly involved in the digestion, absorption, and processing of the required additional nutrients show response to these states. During lactation, the rumen, upper intestine, and liver increase in size, and more energy is spent on Na+,K+ transport and on protein turnover. The massive endocrine influences during lactation suggest that the metabolism of other tissues besides these and mammary tissue would be influenced, but evidence is rather sparse. Ion transport and protein metabolism in some muscles may indeed be increased. Although substrate cycles characteristically account for a substantially smaller portion of the energy expenditure in the intact animal than do ion transport and protein turnover, stage of lactation influences some of these cycles, particularly the triacylglycerol fatty acid cycle. The needs for additional quantitative in vivo measurements of metabolic conversions and for mechanistic model description of metabolic events in nonmammary tissues are discussed.

Fifteen (control) cows were injected with saline; 28 cows were treated with rbST (15 with 10.3 and 13 with 20.6 mg/d). Fourteen of the 28 treated cows had between injected with rbST in the previous lactation. A total of 29 cows in the present trial had not received rbST in previous lactation. Treatment injections were started between wk 4 and 5 of lactation and continued for 266 consecutive days. Milk production, fee intake and efficiency, and BW data were recorded for 3 wk before and 3 wk after a 38-wk rbST treatment period. Administration of rbST increased average FCM yields in the current lactation by 19%, increased feed energy intake by 7%, and decreased feed conversion (energy intake per unit FCM output) by 17%. Previous treatment with rbST did not significantly affect current milk production but caused a nonsignificant increase in feed intake and a significant, unfavorable, increase in feed conversion of 12%. The results suggest that the advantages of rbST in terms of increased milk yield are maintained for a second consecutive lactation of rbST administration. However, the advantages of rbST in terms of improved feed conversion may be substantially reduced in a second consecutive lactation of administration.

Recombinant bST at daily dosages of 0, 10.3, 20.6, and 41.2 mg/d were injected for 266 d into 8, 10, 9, and 9 Holstein cows, respectively. Treatment effects of recombinant bST were assessed for milk production traits, BW, blood components, and health and reproductive variables. Data reported compare controls to all bST-treated cows. There was an average increase of 18% in 3.5% FCM for bST versus control cows. This increase resulted in enhanced feed efficiency for bST cows, as their DM intakes were not elevated above those of the control cows. Recovery of BW was similar between control and bST groups. Milk composition was unaffected except for a slight decrease in protein percentage during the first 9 wk of treatment, and an elevated SCC between wk 19 and 28. Blood parameters were not different between control and bST cows, except for hematocrit, which decreased with bST treatment. The only health and reproductive parameters affected by bST were mastitis and days open, which were increased in the highest dosage groups.

Thirty-four multiparous and primiparous Holstein cows were utilized to examine the association between the response to long-term administration of recombinant bovine somatotropin and the cow's phenotypic and genetic production potential. Cows representing a range of phenotypic and genetic production potentials were assigned to one of four treatment groups: 0, 12.5, 25.0, or 50.0 mg recombinant bovine somatotropin daily. They were injected daily for 266 d beginning on d 24 to 35 postpartum. Pretreatment milk and fat yields were used to predict daily yields over the lactation and allowed treatment groups to serve as their own controls. Actual minus predicted yield estimated the response to treatment for milk, fat, and FCM for each cow. Milk composition (fat, protein, and lactose percentage) was not significantly affected by treatment. Response in yield for milk, fat, and FCM was significant during the treatment period (266 d). Milk yield increased by 18.5, 19.9, and 21.4%; fat yield increased by 13.4, 20.3, and 18.1%; and FCM increased by 16.3%, 19.7%, and 21.1% after receipt of 12.5, 25.0 and 50.0 mg recombinant bovine somatotropin, respectively. Differences in response were not significant. The dramatic effect recombinant bovine somatotropin has on production requires that alternative approaches be adopted in the future for accurate genetic evaluation of sires and dams if somatotropin is discriminantly used in the national herd.

Oxygen consumption and ouabain-sensitive respiration was measured for liver biopsies from lactating and non-lactating ewes and for hepatocytes isolated from mature, dry ewes. O2 consumption, ouabain-sensitive respiration and 86Rb+ uptake were also measured for hepatocytes isolated from lambs, fed adult sheep and adult sheep starved for 5 d. Ouabain-sensitive respiration in the liver of ewes at peak lactation accounted for 45% of the total liver O2 consumption. This percentage was 24-37% higher (P less than 0.05) than measurements made during late lactation and during the non-lactating period. Total O2 consumption and ouabain-sensitive respiration rates of lamb hepatocytes were greater (P less than 0.05) than similar measurements for hepatocytes isolated from adult sheep. Ouabain-sensitive 86Rb+ uptake by hepatocytes from fed sheep was up to six times greater (P less than 0.05) than that by cells from starved sheep. The magnitude of ouabain-sensitive respiration of hepatocytes from starved sheep was 62% lower (P less than 0.05) than that for hepatocytes from fed sheep.

The objectives of the current study were to 1) determine whether a fish–meal–supplemented diet fed to ewes during late gestation and early lactation would increase the proportion of docosahexaenoic acid (22:6n–3) in colostrum and milk and 2) examine the subsequent effect on the plasma fatty acid profile of nursing lambs. Eight gestating ewes (Rideau–Arcott; 97 ± 5 kg of initial BW; 100 d of gestation) were used in a completely randomized design. Ewes were individually housed and fed a control diet (supplemented with soybean meal) or a fish–meal–supplemented diet for 6 wk before lambing and throughout 7 wk of lactation. Colostrum at d 0 and milk samples at d 36 and 49 of lactation were collected. Blood samples were collected from lambs throughout the preweaning period (at 0, 36, and 49 d of age). Fatty acids of the samples were analyzed by GLC. The ewes fed the fish–meal–supplemented diet had greater (P ⩽ 0.013) percentages (g⁄100 g of total fatty acids) of eicosapentaenoic acid (20:5n–3, 0.16 vs. 0.08), docosahexaenoic acid (0.33 vs. 0.09), total n–3PUFA (2.72 vs. 1.91), total CLA (0.83 vs. 0.64), and total very long chain n–3–PUFA (>C18, 0.70 vs. 0.38), in colostrum and milk compared with the ewes fed the control diet. However, these fatty acids, excluding total n–3–PUFA, did not change over time, nor was there an interaction between diet and time. The percentage of total SFA was increased (P 0.012) linearly over time without having any diet effect. The ratio of n–6–PUFA to n–3–PUFA in colostrum and milk from the control group was greater (P = 0.003) than that of the fishmeal–supplemented group. This ratio was decreased over time (P = 0.001). At birth (d 0), lambs born to the fish–meal–supplemented ewes had greater (P = 0.001) plasma concentrations (g⁄100 g of total fatty acids) of eicosapentaenoic acid, docosahexaenoic acid, and total very long chain n–3–PUFA than the lambs born to the control ewes. The concentrations of these fatty acids were further increased over time (P = 0.001) for the lambs nursing ewes fed the fish–meal–supplemented diet. The present findings suggest that the concentrations of docosahexaenoic acid in ewe colostrum and milk can be enhanced through diet supplementation with fish meal. The docosahexaenoic acid status of their suckling lambs can also be further enhanced, and this may contribute to improve neural tissue development and overall performance of suckling lambs. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is a key mineral essential to nearly every aspect of metabolism in a dairy cow and needs to be supplied in sufficient quantity. However, dairy cows use less than 40% of dietary P; the rest is excreted mainly in feces, which can lead to environmental pollution. The objective of this study was to develop empirical models of P utilization and evaluate an extant mechanistic model. Data were collected from 12 lactating Holstein cows (678±17 kg body weight, 30 to 52 DIM) fed various amounts of P ranging from 63 to 101 g/d. Dry matter intake (DMI), P intake (total, tP, and digestible, dP), P excreted in feces and urine, P secreted in milk, and plasma P were recorded. An empirical model was developed using the REG procedure in SAS. Digestible P intake was highly related to fecal P, explaining 73.4% of the variation. Adding tP to the regression increased the r2 to 99.6% (Fecal P, g/d = 34.2 + 0.59 tP - 0.85 dP). Urinary P excretion correlated best with plasma P but the relationship was not significant, probably because within the range of P fed, threshold plasma P (3 mmol/L) was not reached. Milk P secretion best related to DMI (r2=0.34), with addition of tP to the model increasing the r2 to 45.2% (Milk P, g/d = 0.00046 DMI + 0.08 tP). The data were also inputted to an extant mechanistic P model to generate predictions of fecal P values and the results evaluated using mean square prediction error (MSPE). The difference between overall observed (50.1 g/d) and predicted mean (54.2 g/d) fecal P output was 4.1 g/d. Root MSPE was 8.2 g/d, which was 16% of observed mean. Although most of the calculated error (75%) was due to random variation, 24% was due to central deviation from the mean due to overestimation of fecal P. This bias is most probably because the model was developed on cows fed grass silagebased diets while in the current experiment, the cows were fed corn silage/alfalfa haylage-based diets. Both analyses show that dietary manipulation of dP can reduce P excretion but under current conditions, urinary P excretion does not pose environmental problems. However, there is a need to calibrate the extant model to make it more relevant to cows in North America. [ABSTRACT FROM AUTHOR]

The objective of this study was to validate the efficacy of a radiotelemetric bolus (RTB) to detect changes in ruminal temperature resulting from (1) systemic illnesses that are associated with febrile responses and (2) subacute ruminal acidosis (SARA). Eight rumenfistulated, lactating Holstein cows (586 ± 37 kg of body weight, 106 ± 18 d in milk) were used in a replicated 4 x 4 Latin square design with a 2 x 2 factorial arrangement. Each period consisted of 21 d. The factors were 2 diets, a moderate forage:concentrate [MFC; 52:48; % of dry matter (DM)] or a high forage:concentrate (HFC; 65:35, % of DM) total mixed ration, and a challenge with a single intramammary injection of lipopolysaccharide (LPS; 100 µg derived from Escherichia coli 0111:B4) or no LPS (sterile saline). Thus, the 4 resulting treatments were (1) MFC with LPS challenge, (2) MFC with saline, (3) HFC with LPS challenge, and (4) HFC with saline. Cows were fed at 0800 and 1400 h daily. Cows received the intramammary injections at 0900 h of d 21. Ruminal pH and ruminal temperature were also measured on d 21 every minute via an indwelling logging system that resided in the ventral sac of the rumen and via a radiotelemetric bolus that resided in the reticulum. Vaginal temperature was also recorded every minute via temperature loggers. Prior to LPS injection, the duration of rumen pH below 5.6 (indicative of SARA) was higher in cows receiving MFC than cows receiving HFC (148 ± 24 and 62 ± 24 min/d, respectively). The temperature measured at the same time via RTB was higher for MFC than HFC cows (167 ± 21 vs. 104 vs. 21 min/d above 38.8°C, respectively). The following day, cows challenged with LPS showed signs of mastitis within the injected quarters, depressed DM intake, decreased milk yield, and a peak vaginal temperature of 41.3 ± 0.1°C 5.5 h after the LPS injection. The RTB system successfully detected a fever response parallel to that measured by the vaginal loggers but temperature peak detected by RTB was, on average, 0.5°C lower than that detected by the vaginal logger. Although the RTB system was able to detect a temperature response to the diet effect before LPS challenge, it was unable to detect this effect during the LPS challenge, likely because cows receiving the LPS challenge had decreased feed consumption. In conclusion, radiotelemetry has the potential to improve the detection of SARA and fever on farm. [ABSTRACT FROM AUTHOR]

A long-term monensin supplementation trial involving lactating dairy cattle was conducted to determine the effect of monensin on the quantity and diversity of rumen methanogens in vivo. Fourteen cows were paired on the basis of days in milk and parity and allocated to one of two treatment groups,'receiving (i) a control total mixed ration (TMR) or (ii) a TMR with 24 mg of monensin premix/kg of diet dry matter. Rumen fluid was obtained using an ororuminal probe on day -15 (baseline) and days 20, 90, and 180 following treatment. Throughout the 6-month experiment, the quantity of rumen methanogens was not significantly affected by monensin supplementation, as measured by quantitative real-time PCR. The diversity of the rumen methano- gen population was investigated using denaturing gradient gel electrophoresis (DGGE) and 16S rRNA clone gene libraries. DGGE analysis at each sampling point indicated that the molecular diversity of rumen methanogens from monensin-treated cattle was not significantly different from that of rumen methanogens from control cattle. 16S rRNA gene libraries were constructed from samples obtained from the rumen fluids of five cows, with a total of 166 clones examined. Eleven unique 16S rRNA sequences or phylotypes were identified, five of which have not been recognized previously. The majority of clones (98.2%) belonged to the genus Methanobrevibacter, with all libraries containing Methanobrevibacter strains M6 and SM9 and a novel phylotype, UG3322.2. Overall, long-term monensin supplementation was not found to significantly alter the quantity or diversity of methanogens in the rumens of lactating dairy cattle in the present study. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the effect of monensin (MN) and dietary soybean oil (SBO) on milk fat percentage and milk fatty acid (FA) profile. The study was conducted as a randomized complete block design with a 2 x 3 factorial treatment arrangement using 72 lactating multiparous Holstein dairy cows (138 ± 24 d in milk). Treatments were [dry matter (DM) basis] as follows: 1) control total mixed ration (TMR, no MN) with no supplemental SBO; 2) MN-treated TMR (22 g of MN/kg of DM) with no supplemental SBO; 3) control TMR including 1.7% SBO; 4) MN-treated TMR including 1.7% SBO; 5) control TMR including 3.4% SBO; and 6) MN-treated TMR including 3.4% SBO. The TMR (% of DM; corn silage, 31.6%; haylage, 21.2%; hay, 4.2%; high-moisture corn, 18.8%; soy hulls, 3.3%; and protein supplement, 20.9%) was offered ad libitum. The experiment consisted of a 2-wk baseline, a 3-wk adaptation, and a 2-wk collection period. Monensin, SBO, and their interaction linearly reduced milk fat percentage. Cows receiving SBO with no added MN (treatments 3 and 5) had 4.5 and 14.2% decreases in milk fat percentage, respectively. Cows receiving SBO with added MN (treatments 4 and 6) had 16.5 and 35.1% decreases in milk fat percentage, respectively. However, the interaction effect of MN and SBO on fat yield was not significant. Monensin reduced milk fat yield by 6.6%. Soybean oil linearly reduced milk fat yield and protein percentage and linearly increased milk yield and milk protein yield. Monensin and SBO reduced 4% fat-corrected milk and had no effect on DM intake. Monensin interacted with SBO to linearly increase milk fat concentration (g/100 g of FA) of total trans-18:l in milk fat including trans-6 to 8, trans-9, trans-10, trans-11, trans-12 18:1 and the concentration of total conjugated linoleic acid isomers including cis-9, trans-11 18:2; trans-9, cis-11 18:2; and trans-10, cis-12 18:2. Also, the interaction increased milk concentration of polyunsaturated fatty acids. Monensin and SBO linearly reduced, with no significant interaction, milk concentration (g/100 g of FA) of short- and medium -chain fatty acids (

The objective of this study was to evaluate the effects of level of concentrate acidogenic value (AV) and forage particle size on ruminal pH and feed intake in lactating dairy cows. Two isoenergetic (net energy for lactation = 1.5 ± 0.01 Mcal/kg) and isonitrogenous (crude protein = 17.4 ± 0.1% dry matter) concentrates with either a low AV or high AV were formulated and fed in a total mixed ration with either coarsely or finely chopped corn silage and alfalfa haylage ad libitum. Four rumen-fistulated cows (114 ± 14 d in milk) were randomly assigned to 1 of the 4 treatments in a 4 x 4 Latin square with a 2 x 2 factorial treatment arrangement. Each period consisted of 3-wk (14-d treatment adaptation and 7-d data collection). Increasing the concentrate AV decreased the mean pH (from 6.07 to 5.97) and minimum pH (from 5.49 to 5.34). Cows fed high-AV diets spent a longer time below pH 5.6 (135.1 vs. 236.7 min/d; low-AV diet vs. high-AV diet, respectively) and pH 5.8 (290.0 vs. 480.6 min/d; low-AV diet vs. high-AV diet, respectively) than cows fed low-AV diets. Increasing forage particle size had no effect on the mean and minimum ruminal pH. There was an interaction between concentrate AV and forage particle size on maximum ruminal pH. Increasing forage particle size increased the maximum pH for cows fed the high-AV concentrate (6.69 vs. 6.72; low-AV diet vs. high-AV diet, respectively) and had no effect on the maximum pH for cows fed the low-AV concentrate (6.98 vs. 6.76; low-AV diet vs. high-AV diet, respectively). Increasing the concentrate AV did not affect dry matter intake but reduced neutral detergent fiber intake from 9.7 to 8.8 kg/d. Milk fat content was negatively correlated with time and area below pH 5.6 (time below, r = -0.51; area below, r = -0.56) and pH 5.8 (time below, r = -0.42; area below, r = -0.54). These results suggest that coarse forage particle size can attenuate drops in ruminal pH. However, the ameliorating effects of forage particle size on drops in ruminal pH were more apparent for high-AV diets than for low-AV diets. The AV approach combined with physically effective neutral detergent fiber would therefore improve the formulation of diets and help to mitigate subacute ruminal acidosis in dairy cows. [ABSTRACT FROM AUTHOR]