Risk factors associated with bulk tank standard plate count,bulk tank coliform count,and the presence of Staphylococcus aureus on organic and conventional dairy farms in the United States

The purpose of this study was to assess the association of bulk tank milk standard plate counts, bulk tank coliform counts (CC), and the presence of Staphylococcus aureus in bulk tank milk with various management and farm characteristics on organic and conventional dairy farms throughout New York, Wisconsin, and Oregon. Data from size-matched organic farms (n = 192), conventional nongrazing farms (n = 64), and conventional grazing farms (n = 36) were collected at a single visit for each farm. Of the 292 farms visited, 290 bulk tank milk samples were collected. Statistical models were created using data from all herds in the study, as well as exclusively for the organic subset of herds. Because of incomplete data, 267 of 290 herds were analyzed for total herd modeling, and 173 of 190 organic herds were analyzed for the organic herd modeling. Overall, more bulk tanks from organic farms had Staph. aureus cultured from them (62% of organic herds, 42% conventional nongrazing herds, and 43% of conventional grazing herds), whereas fewer organic herds had a high CC, defined as ≥50 cfu/mL, than conventional farms in the study. A high standard plate count (×1,000 cfu/mL) was associated with decreased body condition score of adult cows and decreased milk production in both models. Several variables were significant only in the model created using all herds or only in organic herds. The presence of Staph. aureus in the bulk tank milk was associated with fewer people treating mastitis, increased age of housing, and a higher percentage of cows with 3 or fewer teats in both the organic and total herd models. The Staph. aureus total herd model also showed a relationship with fewer first-lactation animals, higher hock scores, and less use of automatic takeoffs at milking. High bulk tank CC was related to feeding a total mixed ration and using natural service in nonlactating heifers in both models. Overall, attentive management and use of outside resources were useful with regard to CC on organic farms. In all models except the organic CC model, we observed an association with the average reported somatic cell count from 3 mo before the herd visit, indicating that many of the regularly tested milk quality parameters are interconnected. In conclusion, we found that conventional and organic farms are similar in regard to overall herd management, but each grazing system faces unique challenges when managing milk quality.     

A field study of dietary interactions with monensin on milk fat percentage in lactating dairy cattle

Ninety-one Ontario Holstein dairy herds were surveyed about their lactating cow ration and use of a premix containing monensin to identify possible dietary interactions with monensin on milk fat suppression. All herds were enrolled in Ontario Dairy Herd Improvement (DHI) milk recording, and results from four DHI tests were used. Herd mean fat tests were calculated only for cows between 100 and 200 d in milk to avoid potential confounding due to stage of lactation. Wet forage and total mixed ration (TMR) samples from all herds were evaluated for particle size using the Penn State Particle Size Separator. Of the herds using monensin (n = 58), the dose (per kg of dry matter) ranged from 9 to 14 mg/kg in TMR-fed herds and from approximately 9 to 23 mg/kg in herds in which concentrates were fed separately from forages (component-fed). Of the samples submitted for particle size evaluation, 15% of the haylage (n = 80), 14% of the corn silage (n = 79), and 42% of the TMR (n = 58) samples were classified as having low fiber. There was a significant negative univariable association between monensin and mean milk fat percentage. Monensin significantly reduced milk fat percentage in TMR-fed but not component-fed herds. Fiber length significantly interacted with monensin in TMR-fed herds: Herds that had low fiber in their TMR (< or = 6.0% in the top screen) were susceptible to milk fat decrease by monensin, whereas herds that had adequate fiber (> 6.0%) were not. Monensin also significantly reduced milk fat percentage in herds receiving diets low in nonstructural carbohydrate (< 40.2%) but not in those receiving diets high in NSC (> or = 40.2%). The results of this study suggest that there are significant interactions between monensin and certain dietary factors on milk fat suppression in Holstein dairy herds.     

Long-term effects of feeding monensin on milk fatty acid composition in lactating dairy cows

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.     

A meta-analysis of the impact of monensin in lactating dairy cattle. Part 2. Production effects

A meta-analysis of the impact of monensin on production outcomes in dairy cattle was conducted using the 36 papers and 77 trials that contained eligible data. Statistical analyses were conducted in STATA and included a consideration of fixed or random effects models, assessment of publication bias, and impact of influential studies. Meta-regression was used to investigate sources of heterogeneity of response. There were 71 trials containing data from 255 trial sites and 9,677 cows examining milk production and composition. Monensin use in lactating dairy cattle significantly decreased dry matter intake by 0.3 kg, but increased milk yield by 0.7 kg and improved milk production efficiency by 2.5%. Monensin decreased milk fat percentage 0.13%, but had no effect on milk fat yield; however, there was significant heterogeneity between studies for both of these responses. Milk protein percentage was decreased 0.03%, but protein yield was increased 0.016 kg/d with treatment. Monensin had no effect on milk lactose percentage. Monensin increased body condition score by 0.03 and similarly improved body weight change (0.06 kg/d). Analysis of milk fatty acid profile data indicated that monensin was associated with a reduction of short-chain fatty acids (from 1 to 12% reduction) and stearic acid (−7.8%). The impact of monensin on linoleic and linolenic acids was variable, but monensin significantly increased conjugated linoleic acid (22%). Meta-regression of the effect of monensin on milk component percentages and yields indicated an influence of delivery method, stage of lactation, dose, and diet. Increasing concentrations of C18:1 in the diet enhanced the effect of monensin on decreasing milk fat yield, whereas increasing the rumen peptide balance increased the effect of monensin on milk protein yield. These findings indicate a benefit of monensin for improving milk production efficiency while maintaining body condition. The effect of monensin on milk fat percentage and yield was influenced by diet.     

Long-term effects of feeding monensin on methane production in lactating dairy cows

The objective of this study was to determine the long-term effects of feeding monensin on methane (CH₄) production 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 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/kg of dry matter) fed ad libitum. The animals were fed and milked twice daily (feeding at 0830 and 1300 h; milking at 0500 and 1500 h) and CH₄ production was measured prior to introducing the treatments and monthly thereafter for 6 mo using an open-circuit indirect calorimetry system. Monensin reduced CH₄ production by 7% (expressed as grams per day) and by 9% (expressed as grams per kilogram of body weight), which were sustained for 6 mo (mean, 458.7 vs. 428.7 ± 7.75 g/d and 0.738 vs. 0.675 ± 0.0141, control vs. monensin, respectively). Monensin reduced milk fat percentage by 9% (3.90 vs. 3.53 ± 0.098%, control vs. monensin, respectively) and reduced milk protein by 4% (3.37 vs. 3.23 ± 0.031%, control vs. monensin, respectively). Monensin did not affect the dry matter intake or milk yield of the cows. These results suggest that medicating a 60:40 forage-to-concentrate TMR with 24 mg of Rumensin Premix/kg of dry matter is a viable strategy for reducing CH₄ production in lactating Holstein dairy cows.     

Management of Wisconsin dairy herds enrolled in milk quality teams

A study was conducted to characterize Wisconsin dairy herds that enrolled in a team-based milk quality improvement program and to assess association of specific management practices with milking efficiency and milk quality. Management and financial data were obtained from dairy farms (n = 180) that participated in the program. Upon enrollment, herds reported a median bulk milk somatic cell count (SCC) of 333,500 cells/mL, an average of 125 lactating cows, and a mean rolling-herd average of 10,100 kg. Many management practices and bulk milk SCC were strongly associated with herd size and facility type. Managers of herds housed in freestall barns adopted more standardized procedures and recommended management practices compared with managers of herds housed in stall barns. Those managers also reported less bulk milk SCC and greater milk yields, and had a tendency for lower prevalence of subclinical mastitis and reduced estimates of the incidence of clinical mastitis. Managers of freestall herds received more quality premiums for milk shipped, estimated that they had fewer financial losses related to mastitis, and reported more efficient milking performance. A more efficient milking performance did not increase estimates of clinical mastitis or bulk milk SCC. In herds having freestalls, frequent training of employees seemed to be the fundamental factor that increased milking efficiency. Bulk milk SCC was positively associated with standard plate count, estimated rate of clinical mastitis, prevalence of subclinical mastitis, numbers of cows culled for mastitis, and estimated financial losses attributable to mastitis. Herds reporting high bulk milk SCC had an increased prevalence of subclinical mastitis, but incidence did not differ among bulk milk SCC categories. Overall, herds did not discuss milk quality frequently with dairy professionals, and herds having greater bulk milk SCC reported less consultation with their herd veterinarian.     

A high dose of monensin does not reduce methane emissions of dairy cows offered pasture supplemented with grain

The primary objective of our research was to determine the effect of a high dose of monensin supplementation on enteric CH₄ emissions of dairy cows offered a ryegrass pasture diet supplemented with grain. An additional objective was to evaluate effects on milk production and rumen function, because a commensurate improvement in milk production could lead to adoption of monensin as a profitable strategy for methane abatement. Two experiments were conducted (grazing and respiratory chambers) and in both experiments monensin (471 mg/d) was topdressed on 4 kg (dry matter)/d of rolled barley grain offered in a feed trough twice daily at milking times. In the grazing experiment, 50 Holstein-Friesian cows were assigned randomly to 1 of 2 groups (control or monensin). Cows grazed together as a single herd on a predominantly ryegrass sward and received monensin over a 12-wk period, during which time measurements of milk production and body weight change were made. The SF₆ tracer technique was used to estimate methane production of 30 of the 50 cows (15 control cows and 15 monensin cows) for 3 consecutive days in wk 3, 5, 8, and 12 of treatment. Samples of rumen fluid were collected per fistula from 8 of the 50 cows (4 per diet) on 2 consecutive days in wk 3, 5, 8, and 12 of treatment and analyzed for volatile fatty acids and ammonia-N. In the metabolic chamber experiment, 10 pairs of lactating dairy cows (control and monensin) were used to determine the effects of monensin on methane emissions, dry matter intake, milk production, and body weight change over a 10-wk period. Methane emissions were measured by placing cows in respiration chambers for 2 d at wk 5 and 10 of treatment. Cows received fresh ryegrass pasture harvested daily. Monensin did not affect methane production in either the grazing experiment (g/d, g/kg of milk) or the chamber experiment (g/d, g/kg of dry matter intake, g/kg of milk). In both experiments, milk production did not increase with addition of monensin to the diet. Monensin had no effect on body weight changes in either experiment. Monensin did not affect volatile fatty acids or ammonia-N in rumen fluid, but the acetate to propionate ratio tended to decrease. Monensin did not improve milk production of grazing dairy cows and no effect on enteric methane emissions was observed, indicating that monensin cannot be promoted as a viable mitigation strategy for dairy cows grazing ryegrass pasture supplemented with grain.     

Effects of monensin and dietary soybean oil on milk fat percentage and milk fatty acid profile in lactating dairy cows

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 × 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-18:1 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 (<C16). Soybean oil reduced total saturated FA and increased total monounsaturated FA. These results suggest that monensin reduces milk fat percentage and this effect is accentuated when SBO is added to the ration.     

Monitoring the bulk milk antibody response to bovine viral diarrhea in dairy herds vaccinated with inactivated vaccines

This study was designed to determine long-term responses in dairy herds after vaccination with 1 of 3 inactivated bovine viral diarrhea virus (BVDV) vaccines with regard to antibodies against p80 protein in bulk tank milk samples, as detected by ELISA. In the present study, 29 dairy herds were vaccinated with Bovilis BVD (MSD Animal Health, Milton Keynes, UK), 11 with Hiprabovis Balance (Laboratorios Hipra, Amer, Spain), and 9 with Pregsure BVD (Zoetis, Florham Park, NJ). In these herds, bulk tank milk samples were collected and examined at the time of the first vaccination and every 6 mo during a 3-yr period. Samples were analyzed with a commercial ELISA test for the p80 protein of BVDV. The results demonstrated that vaccination affected the level of antibodies against p80. Hence, vaccination status should be taken into consideration when interpreting bulk tank milk antibody tests.     

Anti-methanogenic effects of monensin in dairy and beef cattle: A meta-analysis

Monensin is a widely used feed additive with the potential to minimize methane (CH₄) emissions from cattle. Several studies have investigated the effects of monensin on CH₄, but findings have been inconsistent. The objective of the present study was to conduct meta-analyses to quantitatively summarize the effect of monensin on CH₄ production (g/d) and the percentage of dietary gross energy lost as CH₄ (Y_m) in dairy cows and beef steers. Data from 22 controlled studies were used. Heterogeneity of the monensin effects were estimated using random effect models. Due to significant heterogeneity (>68%) in both dairy and beef studies, the random effect models were then extended to mixed effect models by including fixed effects of DMI, dietary nutrient contents, monensin dose, and length of monensin treatment period. Monensin reduced Y_m from 5.97 to 5.43% and diets with greater neutral detergent fiber contents (g/kg of dry matter) tended to enhance the monensin effect on CH₄ in beef steers. When adjusted for the neutral detergent fiber effect, monensin supplementation [average 32 mg/kg of dry matter intake (DMI)] reduced CH₄ emissions from beef steers by 19 ± 4 g/d. Dietary ether extract content and DMI had a positive and a negative effect on monensin in dairy cows, respectively. When adjusted for these 2 effects in the final mixed-effect model, monensin feeding (average 21 mg/kg of DMI) was associated with a 6 ± 3 g/d reduction in CH₄ emissions in dairy cows. When analyzed across dairy and beef cattle studies, DMI or monensin dose (mg/kg of DMI) tended to decrease or increase the effect of monensin in reducing methane emissions, respectively. Methane mitigation effects of monensin in dairy cows (–12 ± 6 g/d) and beef steers (–14 ± 6 g/d) became similar when adjusted for the monensin dose differences between dairy cow and beef steer studies. When adjusted for DMI differences, monensin reduced Y_m in dairy cows (–0.23 ± 0.14) and beef steers (–0.33 ± 0.16). Monensin treatment period length did not significantly modify the monensin effects in dairy cow or beef steer studies. Overall, monensin had stronger antimethanogenic effects in beef steers than dairy cows, but the effects in dairy cows could potentially be improved by dietary composition modifications and increasing the monensin dose.     

Evaluation of national surveillance methods for detection of Irish dairy herds infected with Mycobacterium avium ssp. paratuberculosis

The aim of this study was to evaluate the utility and cost-effectiveness of a range of national surveillance methods for paratuberculosis in Irish dairy herds. We simulated alternative surveillance strategies applied to dairy cattle herds for the detection of Mycobacterium avium ssp. paratuberculosis (MAP)-infected herds (case-detection) or for estimation of confidence of herd freedom from infection (assurance testing). Strategies simulated included whole-herd milk or serum serology, serology on cull cows at slaughter, bulk milk tank serology, environmental testing, and pooled fecal testing. None of the strategies evaluated were ideal for widespread national case-detection surveillance. Herd testing with milk or serum ELISA or pooled fecal testing were the most effective methods currently available for detection of MAP-infected herds, with median herd sensitivity >60% and 100% herd specificity, although they are relatively expensive for widespread use. Environmental sampling shows promise as an alternative, with median herd sensitivity of 69%, but is also expensive unless samples can be pooled and requires further validation under Irish conditions. Bulk tank milk testing is the lowest cost option and may be useful for detecting high-prevalence herds but had median herd sensitivity <10% and positive predictive value of 85%. Cull cow sampling strategies were also lower cost but had median herd sensitivity <40% and herd positive predictive values of <50%, resulting in an increased number of test-positive herds, each of which requires follow-up herd testing to clarify status. Possible false-positive herd testing results associated with prior tuberculosis testing also presented logistical issues for both cull cow and bulk milk testing. Whole-herd milk or serum ELISA testing are currently the preferred testing strategies to estimate confidence of herd freedom from MAP in dairy herds due to the good technical performance and moderate cost of these strategies for individual herd testing. Cull cow serology and bulk tank milk sampling provide only minimal assurance value, with confidence of herd freedom increasing only minimally above the prior estimate. Different testing strategies should be considered when deciding on cost-effective approaches for case-detection compared with those used for building confidence of herd freedom (assurance testing) as part of a national program.     

Milk coagulation ability of five dairy cattle breeds

Samples of herd milk (506) were analyzed to assess sources of variation for milk coagulation properties (MCP) for 5 different dairy cattle breeds. Data were recorded in 55 single-breed dairy herds in the Trento province, a mountain area in northeast Italy. The 5 cattle breeds were Holstein-Friesian (8 herds), Brown Swiss (16 herds), Simmental (10 herds), Rendena (13 herds), and Alpine Gray (8 herds). Herd milk samples were analyzed for the MCP traits, milk rennet coagulation time (RCT), curd-firming time, and curd firmness (a₃₀), as well as protein and fat percentages, somatic cell count, Soxhlet-Henkel acidity, and bacterial count. An ANOVA was performed to study the effect of breed, herd within breed, DIM, month of lactation, protein and fat percentages, somatic cell score, titratable acidity, and log bacterial count within breed on MCP. Breed was the most important source of variation. In particular, the Rendena breed showed the best MCP traits at 13.5 min and 27.0 mm for RCT and a₃₀, respectively. The Holstein-Friesian breed had the worst coagulation properties at 18.0 min and 17.5 mm for RCT and a₃₀, respectively. The other 3 breeds showed intermediate coagulation properties. The RCT values were better at the beginning of lactation, whereas RCT and a₃₀ values were better in September and October (14.3 min and 25.7 mm, respectively). Among the composition traits, only the titratable acidity affected MCP traits of herd milk positively.     

A meta-analysis of the impact of monensin in lactating dairy cattle. Part 1. Metabolic effects

A meta-analysis of the impact of monensin on metabolism of dairy cattle was conducted following a search of the literature. A total of 59 studies with monensin feeding in dairy cattle were identified in which 30 papers and 45 trials contained metabolic data. The β-hydroxybutyrate (BHBA) data were obtained from over 4,000 cows and 115 trial sites. Data for each trial were extracted and analyzed using meta-analysis software in Stata. Estimated effect sizes of monensin were calculated on blood concentrations of BHBA, acetoacetate, nonesterified fatty acids (NEFA), glucose, cholesterol, urea, calcium, insulin, and milk urea. Monensin use in lactating dairy cattle significantly reduced blood concentrations of BHBA 13%, acetoacetate 14%, and NEFA 7%. Monensin increased glucose 3% and urea 6%. Monensin had no significant effect on cholesterol, calcium, milk urea, or insulin. Heterogeneity was significant for BHBA and cholesterol [I² (measure of variation beyond chance) = 37 and 54%, respectively]; therefore, random effects models were used for those analytes. Publication bias existed with the monensin effect on BHBA, with a tendency for studies to be published if there was a significant reduction in this ketone. Meta-regression analysis of the effect sizes obtained from the metabolic data showed that method of delivery, timing of administration, stage of lactation, and diet were influential in modifying effect size of monensin treatment. Use of top dress or delivery via a controlled release capsule reduced the magnitude of effect on BHBA (coefficient +0.353); however, top dress use compared with controlled release capsule or total mixed ration enhanced the monensin effect on glucose (coefficient +0.296). There was a greater impact with monensin on reducing BHBA in early lactation (coefficient −0.151) and in pasture-based trials (coefficient −0.194). Use of monensin in both the pre- and postcalving periods was associated with an enhanced impact on NEFA (coefficient −0.254). Monensin had less impact on serum glucose in the pre-calving time period (coefficient −0.237). These findings demonstrate an improvement in the energy metabolism of dairy cows supplemented with monensin.     

Microbiological quality of bulk tank raw milk in Prince Edward Island dairy herds

The objectives of this study were to evaluate microbiological quality of bulk tank milk in Prince Edward Island, to evaluate correlation among milk quality criteria, and to determine seasonal effects on milk quality parameters. Bulk tank raw milk quality was evaluated on all Prince Edward Island dairy herds (n = 235) over a 2-yr period (March 2005 to March 2007). Biweekly total aerobic (TAC), preliminary incubation (PIC), laboratory pasteurization, and coliform (CC) counts were determined using a Petrifilm culture system. Additionally, bulk tank somatic cell count was determined weekly. The mean and median values were 12.8 × 10³ and 4.9 × 10³ cfu/mL for TAC, 29.6 × 10³ and 13 × 10³ cfu/mL for PIC, 87 and 12 cfu/mL for laboratory pasteurization count, 21 and 5 cfu/mL for CC, and 218 × 10³ and 187 × 10³ cells/mL for somatic cell count. There was moderate correlation (0.57) between TAC and PIC. All other correlation coefficients were low (<0.26). Correlation results suggest that a single quality parameter could not predict others used in this study. Seasonal data indicate that 1) in general, all counts tended to be low in winter, 2) the CC and somatic cell count were always high in summer, and 3) TAC tended to be high during summer.     

Effects of monensin and stage of lactation on variation of blood metabolites within twenty-four hours in dairy cows

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, β-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. β-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.     

A meta-analysis of the impact of monensin in lactating dairy cattle. Part 3. Health and reproduction

A meta-analysis of the impact of monensin on health and reproductive outcomes in dairy cattle was conducted. A total of 16 papers were identified with sufficient data and quality to evaluate health and reproductive outcomes for monensin. The available trials provided approximately 9,500 cows with sufficient data for analysis. This provided good statistical power to examine the effects of monensin on health and reproduction. Over all the trials analyzed, monensin decreased the risk of ketosis [relative risk (RR) = 0.75], displaced abomasums (RR = 0.75), and mastitis (RR = 0.91). No significant effects of monensin were found for milk fever, lameness, dystocia, retained placenta, or metritis. Monensin had no effect on first-service conception risk (RR = 0.97) or days to pregnancy (hazard ratio = 0.93). However, the impact of monensin on dystocia, retained placenta, and metritis was heterogeneous for all 3 outcome measures and random effect models were utilized. Causes of the heterogeneity were explored with meta-regression. Days of treatment with monensin before calving increased the risk of dystocia. Delivery method of monensin influenced the incidence of retained placenta and metritis, with risk being lower with controlled release capsule treatment compared with delivery in either topdress or in a total mixed ration. Days of treatment before calving also influenced retained placenta with an increase in risk with more days treated before calving. Improvements in ketosis, displaced abomasums, and mastitis with monensin were achieved. Exposure to prolonged treatment in the dry period with monensin may increase the risk of dystocia and retained placenta.     

Use of monensin controlled-release capsules to reduce methane emissions and improve milk production of dairy cows offered pasture supplemented with grain

We examined the effects of monensin, provided by controlled-release capsules, on the enteric methane emissions and milk production of dairy cows receiving ryegrass pasture and grain. In a grazing experiment, 60 Holstein-Friesian cows were assigned randomly to 1 of 2 groups (control or monensin). Cows in the monensin group received 2 controlled-release capsules, with the second capsule administered 130 d after the first. Milk production was measured for 100 d following insertion of each capsule. The sulfur hexafluoride tracer gas technique was used to measure enteric methane emissions for 4 d starting on d 25 and 81 after insertion of the first capsule, and on d 83 after insertion of the second capsule. All cows grazed together as a single herd on a predominantly ryegrass sward and received 5 kg/d of grain (as-fed basis). In a second experiment, 7 pairs of lactating dairy cows (control and monensin) were used to determine the effects of monensin controlled-release capsules on methane emissions and dry matter intake. Methane emissions were measured on d 75 after capsule insertion by placing cows in respiration chambers for 3 d. Cows received fresh ryegrass pasture harvested daily and 5 kg/d of grain. The release rate of monensin from the capsules used in both experiments was 240 ± 0.072 mg/d, determined over a 100-d period in ruminally cannulated cows. The monensin dose was calculated to be 12 to 14.5 mg/kg of dry matter intake. There was no effect of monensin on methane production in either the grazing experiment (g/d, g/kg of milk solids) or the chamber experiment (g/d, g/kg of dry matter intake). In the grazing study, there was no effect of monensin on milk yield, but monensin increased milk fat yield by 51.5 g/d and tended to increase milk protein yield by 18.5 g/d. Monensin controlled-release capsules improved the efficiency of milk production of grazing dairy cows by increasing the yield of milk solids. However, a higher dose rate of monensin may be needed to reduce methane emissions from cows grazing pasture.     

The impact of cooling ponds in North Central Texas on dairy farm performance

The objective of this study was to determine whether measurable differences existed between farms with and without cooling ponds. Data from Dairy Herd Improvement records for 1999 through 2002 were obtained on 42 herds located in North Central Texas. Nineteen herds had installed cooling ponds, whereas 23 herds had not. Monthly somatic cell counts for each herd were obtained from the Federal Milk Market Administrator. Data were analyzed using the PROC MIXED regression model of SAS. Within and across herd groups, milk production from June to October was significantly lower compared with milk production for the rest of the year. Although there was numerically higher average milk production per cow per day throughout the year for herds that used cooling ponds, differences between herd groups that used or did not use cooling ponds were significant only for August production. Herds without a cooling pond had 4.8 kg/d per cow lower production in August than in the cool-season months of November to May (26.4 ± 0.6 vs. 31.2 ± 0.5 kg/d), whereas the difference in August production was only 2.9 kg/d per cow in herds that used cooling ponds (29.0 ± 0.7 vs. 31.9 ± 0.6 kg/d). Differences caused by seasonal use of a cooling pond in culling, days to first service, days open, percentage of estruses observed, and somatic cell counts were not significant. Bulk tank milk samples cultured for 10 different bacteria showed no difference between cooling pond and noncooling pond herds in 2002. Also, there was no difference in incidence of violations from the Texas Department of Health for herds that used or did not use cooling ponds. However, herds with cooling ponds did have a lower percentage of successful breedings, fewer days dry, and a higher percentage of cows in milk compared with dairy herds that used other forms of cooling. Such differences may or may not be attributed to seasonal use of a cooling pond. Therefore, cooling ponds may provide relief from heat stress without adversely affecting most important measures of herd performance.     

Effect of supplementing myristic acid in dairy cow rations on ruminal methanogenesis and fatty acid profile in milk

The objective of this study was to evaluate the effects of supplementing myristic acid in dairy cow rations on ruminal methanogenesis and the fatty acid profile in milk. Twelve multiparous Holstein dairy cows (710 ± 17.3 kg of live weight; 290 ± 41.9 d in milk) housed in a tie-stall facility were used in the study. 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 (control diet), and 2) the regular milking cow total mixed ration supplemented with 5% myristic acid on a dry matter basis (MA diet). The cows were fed and milked twice daily (feeding, 0830 and 1300 h; milking, 0500 and 1500 h). The experiment was conducted as a completely randomized design and consisted of a 7-d pretrial period when cows were fed the control diet to obtain baseline measurements, a 10-d dietary adaptation period, and a 1-d, 8-h measurement period. The MA diet reduced methane (CH₄) production by 36% (608.2 vs. 390.6 ± 56.46 L/d, control vs. MA diet, respectively) and milk fat percentage by 2.4% (4.2 vs. 4.1 ± 0.006%, control vs. MA diet, respectively). The MA diet increased 14:0 in milk by 139% and cis-9 14:1 by 195%. There was a correlation (r = −0.58) between the 14:0 content in milk and CH₄ production and cis-9 14:1 and CH₄ production (r = −0.47). Myristic acid had no effect on the contents of CLA or trans-10 18:1 and trans-11 18:1 isomers in milk. These results suggest that MA could be used to inhibit the activities of methanogens in ruminant animals without altering the conjugated linoleic acid and trans-18:1 fatty acid profile in milk.