Effect of paratuberculosis on culling, milk production, and milk quality in dairy herds

OBJECTIVE: To determine the effect of paratuberculosis on culling, milk production, and milk quality in infected dairy herds. DESIGN: Cross-sectional study. ANIMALS: 689 lactating dairy cows in 9 herds. PROCEDURE: Milk, blood, and fecal samples were obtained from all cows. Fecal samples were evaluated via mycobacterial culture. Serum samples were tested with a commercially available ELISA for antibodies against Mycobacterium avium subsp paratuberculosis, and preserved milk samples were tested with an ELISA for antibodies against M paratuberculosis. Mixed effect and proportional hazards models were used to determine the effect of paratuberculosis on 305-day milk, fat, and protein production; somatic cell count linear score; and the risk of culling. RESULTS: Cows with positive results of bacteriologic culture of feces and milk ELISA produced less milk, fat, and protein, compared with herdmates with negative results. No difference in 305-day milk or fat production was detected in cows with positive results of serum ELISA, compared with seronegative cows. The 3 survival analyses revealed that cows with positive results of each test were at higher risk of being culled than cows with negative results. Paratuberculosis status, as determined by use of all 3 diagnostic tests, was not associated with milk somatic cell count linear score. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that for the 9 herds in this study, paratuberculosis significantly decreased milk production and cow longevity.     

Association of Mycobacterium avium subspecies paratuberculosis infection with milk production and calving interval in Iranian Holsteins

There are inconsistent results for the association of Mycobacterium avium subspecies paratuberculosis (MAP) infection with production and reproduction in dairy cows. Determination of these associations in each region is essential to encourage participation of dairy cattle producers in disease control programs. This study was conducted in Shiraz, southern Iran, to quantify the association of subclinical MAP infection with 305-day milk production and calving interval in Iranian Holsteins. A total of 21 dairy herds were selected for the study and in each herd, quarter milk samples were collected from ten to 12 dairy cows for PCR analysis. Data about parity, calving interval, length of lactation period, total milk production and 305-day milk production were also provided for each animal. Overall, 252 individual milk samples were collected. Herd- and individual-level prevalence of MAP infection were 23.8% (95% CI, 6.2–41.4%) and 3.2% (95% CI, 1.3–5.1%), respectively based on IS900 nested PCR. The results for 305-day milk production revealed a 248 kg reduction in positive cows compared with negative ones (P = 0.009). When cows from positive herds were compared with cows from negative herds, a 335-kg reduction in 305-day milk production (P = 0.005) and a 30-day increase in calving interval (P = 0.057) were observed in the former group. These findings support the previous results that paratuberculosis infection is negatively associated with the performance of the animals.     

Use of age and milk production data to improve the ability of enzyme-linked immunosorbent assay test results to predict Mycobacterium avium ssp. paratuberculosis fecal culture status.

Cows from 2 California dairies were tested for paratuberculosis at the end of lactation by using fecal culture and a commercially available serum enzyme-linked immunosorbent assay (ELISA) test kit. Individual cow characteristics and production variables were evaluated along with ELISA testing results as predictors of fecal culture status. In multivariable logistic regression analysis, age and a herd-standardized version of 305-day mature equivalent (305 ME) milk production were significant predictors of fecal culture status after adjusting for herd, quarter of the study year, and ELISA sample-to-positive (S/P) ratio. The area under a nonparametric receiver operating characteristic curve was significantly greater for a multivariable model that included age and the level of milk production when compared with a model without these covariates. In conclusion, consideration of cow-level covariates was useful as an aid in predicting Mycobacterium avium ssp. paratuberculosis (MAP) fecal culture status. For a given ELISA S/P ratio, older cows and those with lower 305 ME milk production relative to other cows in the herd were significantly more likely to be shedding MAP in their feces at the end of lactation.     

Comparison of milk and serum enzyme-linked immunosorbent assays for diagnosis of Mycobacterium avium subspecies paratuberculosis infection in dairy cattle.

Milk and serum samples from 35 dairy herds in 17 states were evaluated for cow- and herd-level Mycobacterium avium subspecies paratuberculosis (MAP) antibody test agreement. Evaluation of 6,349 samples suggested moderate agreement between milk and serum enzyme-linked immunosorbent assay (ELISA) results, with a kappa value of 0.50. Cow-level sensitivity (Se) for 18 dairy operations with 1,921 animals was evaluated relative to fecal culture results. At the cow level, the milk ELISA relative Se was not significantly different from that of the serum ELISA (21.2 and 23.5%, respectively). Logistic regression models revealed a positive association between lactation number and milk ELISA status. Non-Holstein cows were more likely to test milk ELISA positive than Holstein cows. Cows in the first 2 weeks of lactation and after week 45 of lactation were more likely to test milk ELISA positive than cows between 3 and 12 weeks of lactation. Milk production > 80% of herd average was negatively associated with testing milk ELISA positive. Animals in the West and Midwest regions were less likely than animals in the Southeast region to test ELISA positive by either test. Estimates for herd-level sensitivity for the milk and serum ELISA, relative to fecal culture results, ranged from 56 to 83%. At the cow and herd levels, milk ELISA performed equivalent to serum ELISA using fecal culture as a reference for MAP infection and has the advantage of decreased labor costs on farms that use Dairy Herd Improvement Association testing.     

Effects of bovine leukemia virus infection on production and reproduction in dairy cattle.

The purpose of this study was to determine the effects of bovine leukemia virus (BLV) infection on production, reproduction and longevity in dairy cattle. The study population was a commercial Holstein dairy herd of approximately 400 milking cows. Cattle were tested for antibodies to BLV at least annually for three years and when culled. Four groups of culled cows were compared: seronegative cows (n = 79), seropositive cows without lymphocytosis (n = 176), seropositive cows with lymphocytosis (> or = 9,000 lymphocytes/microliter) (n = 74), and seropositive cows with lymphosarcoma (n = 29). Seropositive groups of cows were bred more times and had longer calving intervals than seronegative cows. The seropositive groups had greater 305-day ME (mature equivalent) FCM (3.5% fat-corrected milk) per lactation and were older when culled than seronegative cows. However, the percent fat per lactation was greater in seronegative cows. In the last complete lactation, differences in 305-day ME FCM, days open and cull age between groups were reduced and none were significant (p > 0.05). In the cull lactation, only cows with lymphocytosis had reduced milk production relative to seronegative cows, although this difference was not significant. After adjustment for initial production and reproductive values, only seropositive nonlymphocytotic cows were culled at a significantly older age than seronegative cattle. Lymphocytotic cows were culled four months younger on average than nonlymphocytotic seropositive cows. Hence, BLV infected cows had greater milk production on average than uninfected cows. Adverse effects of BLV infection were primarily limited to lymphocytotic cows which were culled earlier and had reduced milk production in the cull lactation.     

Effect of Mycobacterium paratuberculosis infection on production, reproduction, and health traits in US Holsteins

Our objective was to estimate the effect of Mycobacterium paratuberculosis infection on milk, fat, and protein yield deviations, pregnancy rate, lactation somatic cell score, and projected total months in milk (productive life). A serum ELISA and fecal culture for M. paratuberculosis were performed on 4375 Holsteins in 232 DHIA herds throughout the US. Primarily first through third lactation cows (99% of total) were assayed for infection. Trait information (except productive life) was obtained for the lactation concurrent with disease tests. Productive life was total months in milk through a cow's life, which was projected if a cow was still milking. For most analyses, case definition for M. paratuberculosis infection was defined as either an ELISA S/P ratio>or=0.25 or a positive fecal culture for M. paratuberculosis or both. To determine if diagnostic test affected estimates, case definition was redefined to include only cows with ELISA S/P ratios>or=0.25 or only fecal culture-positive cows. Linear models were used to estimate effect of M. paratuberculosis infection on traits. M. paratuberculosis-infected cows (7.89% of cows) produced 303.9 kg less milk/lactation, 11.46 kg less fat/lactation, and 9.49 kg less protein/lactation (P相似文献   

Association between exposure to Neospora caninum and milk production in dairy cows

OBJECTIVE: To determine association between exposure to Neospora caninum and milk production in dairy cows. DESIGN: Prospective observational study. Animals: 565 Holstein cows. PROCEDURE: Cows were classified as seropositive or seronegative to N. caninum within 7 days after calving by use of a kinetic ELISA. Milk production was compared between seropositive and seronegative cows. RESULTS: On the basis of 305-day mature equivalent milk production data, seropositive cows produced less milk (2.8 lb/cow per day) than did seronegative cows. In addition, analysis of results throughout the first 300 days of lactation revealed that after adjusting for effects of lactation number, calving season, clinical mastitis, and lameness, milk weight of seropositive cows was 2.5 lb/cow per day less than that of seronegative cows. CONCLUSIONS AND CLINICAL RELEVANCE: Exposure to N. caninum was associated with a 3 to 4% decrease in milk production. A decrease in milk production of 800 lb/cow for a typical 305-day lactation represents a loss of $128/cow.     

Neospora caninum serostatus and milk production of Holstein cattle

OBJECTIVE: To determine whether Neospora caninum serostatus was associated with milk production among Holstein cattle in Ontario. DESIGN: Case-control study and cross-sectional observational study. ANIMALS: 3,702 Holstein cows in 83 herds (case-control study) and 3,162 Holstein cows in 57 herds. PROCEDURE: Herds in the case-control study were grouped on the basis of N. caninum abortion status. Herds in the observational study were considered representative of Ontario dairy herds. The N. caninum serostatus of individual cows was determined with a kinetic ELISA. Milk production was modeled to compare seropositive with seronegative animals while controlling for parity, days since parturition, and herd clustering. RESULTS: In the case-control study, 305-day milk production of seropositive cows was significantly less than milk production of seronegative cows in herds with abortions attributable to N. caninum infection and in herds with abortions attributable to pathogens other than N. caninum, but not in herds without abortion problems. In the observational study, 305-day milk production for seropositive cows was not significantly different from milk production of seronegative cows. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the association between N. caninum serostatus and milk production in Ontario Holstein dairy cattle may depend on abortion status of the herd. In herds with abortion problems, regardless of cause, N. caninum-seropositive cattle produced less milk, whereas in herds without abortion problems, N. caninum-seropositive cattle produced the same amount of milk as seronegative cattle.     

Relationship between antibodies against Mycobacterium avium subsp. paratuberculosis in milk and shape of lactation curves

To analyze how infection with Mycobacterium avium subsp. paratuberculosis (MAP) affects the shape of lactation curves, a three-level hierarchical test-day model was set up with fat-corrected test-day milk yield (FCTM) as response. Milk samples from 6955 cows in 108 Danish dairy herds were tested with ELISA to detect antibodies against MAP. Optical densities (ODs) recorded on a continuous scale were standardized according to parity and stage of lactation. In addition to standardized ODs (stOD), seven fixed covariates, quadratic terms and first-order interactions were included in the model. Cow and cow nested in herd were included as random effects. Cows of first, second and higher parities were analyzed separately. The lactation curves after peak yield were significantly less persistent in young infected cows, where an increase of one stOD unit was associated with a depression of the milk yield per day through day 305 of 3.7 kg FCTM in first parity and 2.7 kg FCTM in second parity. In second-parity cows, the lactation curve also was both depressed through the entire lactation and more steep after 60 days in milk (DIM). In third and older parities, a significant effect of the quadratic term of stOD indicated exponentially increased losses with increased ODs.     

Characterization of Mycobacterium avium subspecies paratuberculosis disseminated infection in dairy cattle and its association with antemortem test results

Mycobacterium avium subspecies paratuberculosis (MAP) disseminated infection in dairy cattle affects animal health and productivity and is also a potential public health concern. The study objectives were to characterize MAP disseminated infection in dairy cattle and to determine the role of antemortem tests in detecting cattle with disseminated infection. Forty culled dairy cows representing a variety of serum enzyme-linked immunosorbent assay (ELISA) results and body conditions were selected for the study. The physical condition of the cows was assessed via clinical examination prior to euthanasia and blood and feces were collected and tested by serum ELISA and fecal culture, respectively. Fifteen tissues were aseptically collected from each cow during necropsy and cultured for isolation of MAP. Disseminated infection was diagnosed when MAP was isolated in tissues other than the intestines or their associated lymph nodes (LNs) and was distinguished from infection found only in the gastrointestinal tissues and from absence of infection. Of the 40 cows in the study, 21 had MAP disseminated infection. Results showed that 57% (12/21) of cows with disseminated infection had average to heavy body condition and no diarrhea. Cows with disseminated infection had no to minimal gross pathologic evidence of infection in 37% (8/21) of cases. Only 76% (16/21) of cows with disseminated infection had positive historical ELISA results and only 62% (13/21) had a positive ELISA at slaughter. Thus, antemortem evidence of MAP infection was lacking in a high proportion of cows where MAP disseminated infection was confirmed.     

中国荷斯坦奶牛不同地区、泌乳天数及胎次的产奶量校正系数研究

本研究通过对规模化牧场测定日数据进行分析,旨在估计不同地区305 d校正产奶量对应泌乳天数(DIM)的校正系数与胎次校正系数。利用Wood(不完全伽玛)模型对来自不同温度带9个参考群11 749头荷斯坦奶牛2010－2020年间的683 160条测定日产奶量拟合泌乳曲线,估计泌乳曲线参数,计算头胎牛和经产牛1~305 d泌乳天数对应的校正系数,分别分析参考群和验证群305 d校正产奶量和305 d实际累积奶量的差异;利用SAS 9.2中混合线性模型对1~6胎至少有前5个胎记录的牛估计305 d奶量的胎次效应值,并计算1~6胎各胎次的乘法校正系数;比较传统系数和新系数校正结果的差异。结果表明:①参考群头胎牛和经产牛中,泌乳曲线方程的拟合度R²范围分别为0.4593~0.4913和0.5796~0.6341,泌乳高峰日分别为79~85和53 d,泌乳高峰奶量分别为33.1~34.4和46.0~48.6 kg;②对于参考群,头胎牛和经产牛校正系数分别在泌乳≥90 d和泌乳≥30 d基本趋于一致,头胎牛和经产牛泌乳≥60 d的305 d校正产奶量均趋近于305 d实际累积奶量,奶量差值分别在100和200 kg以内;③对于验证群的305 d校正产奶量,头胎牛泌乳≥150 d和经产牛泌乳≥180 d的泌乳天数校正系数适用性更佳,305 d校正产奶量与305 d实际累积奶量比值高于79%;④1~6胎的胎次校正系数分别为1.2121、1.0380、1.0063、1.0000、1.0220和1.0290;⑤与传统系数相比,新泌乳天数校正系数校正效果更好,头胎牛和经产牛新系数校正的305 d奶量较305 d实际累积奶量相差分别在900和700 kg以内;利用新胎次校正系数,2~4胎产奶量可较为准确地校正到5胎成年当量。本研究结果表明,定期更新305 d校正产奶量的泌乳天数与胎次校正系数,便于准确地将不同泌乳天数、不同胎次状态下泌乳牛的产奶量调整到同一基准上,从而更好地比较奶牛个体泌乳性能的高低,为牧场管理提供参考依据。     

Effect of lameness on milk yield in dairy cows

OBJECTIVE: To examine the relationship between lameness and milk yield in dairy cows. DESIGN: Cohort study. ANIMALS: 531 dairy cows. PROCEDURE: Cows affected with lameness were classified into 1 of 3 groups on the basis of type of diseases or lesions observed, including interdigital phlegmon (foot rot), papillomatous digital dermatitis (foot warts), or claw lesions. Cows not affected with lameness were classified as healthy. From Dairy Herd Improvement Association records, 305-day mature equivalent milk yield data were collected at the end of lactation or when the cow left the herd. Milk yield was compared between cows affected with lameness and healthy cows. RESULTS: 167 (31%) cows were affected with lameness during lactation. Lame cows had claw lesions (60%), papillomatous digital dermatitis (31%), or interdigital phlegmon (9%). Milk yield in lame cows with interdigital phlegmon (mean, 17,122 lb) was significantly less, compared with healthy cows (19,007 lb). CONCLUSIONS AND CLINICAL RELEVANCE: In this herd, interdigital phlegmon was associated with a 10% decrease in milk production. Lame cows with claw lesions or papillomatous digital dermatitis produced less milk than healthy cows, but the difference was not significant.     

Evaluation of cost-effectiveness of targeted sampling methods for detection of Mycobacterium avium subsp paratuberculosis infection in dairy herds

OBJECTIVE: To investigate the epidemiologic and financial impacts of targeted sampling of subpopulations of cows, compared with random sampling of all cows, for classification of dairy herd infection status for paratuberculosis. ANIMALS: All cows from 4 infected herds with a low-to-moderate prevalence of paratuberculosis and from 1 noninfected herd in California. PROCEDURE: The infection status of each cow was classified on the basis of results of an ELISA or combined ELISA and fecal culture results. Thirteen sampling schemes designed to randomly sample cows on the basis of lactation number, stage of lactation, and milk production were evaluated. Sampling without replacement was used to obtain a probability of herd detection of paratuberculosis for each evaluated sampling method and for simulated sample sizes between 30 and 150 cows. Marginal cost-effectiveness analysis was used to determine the cost increase relative to the increase in detection probability. RESULTS: Sampling cows in the third or higher lactation and > or = 200 days into lactation yielded the highest detection probability in most instances, resulting in a detection probability that was 1.4 to 2.5 times that obtained by sampling 30 cows in the second or higher lactation. Costs of testing via the alternative method with a 95% detection probability were approximately dollar 300 lower in a high-prevalence herd (31%) and dollar 800 lower in a low-prevalence herd (9%), compared with use of the reference method. CONCLUSIONS AND CLINICAL RELEVANCE: Detection of herds with paratuberculosis could be improved, and costs of testing substantially reduced by sampling targeted groups of cows.     

Relation among body condition score, milk production, and serum urea nitrogen and cholesterol concentrations in high-producing Holstein dairy cows in early lactation.

Body condition scoring (using a 5-point scale with quarter-point divisions) was performed on 66 Holstein dairy cows that began their second or later lactation in August, September, or October 1988. Body condition was scored, beginning on postpartum day 4(+/- 1) and subsequently at postpartum days (+/- 1) 18, 32, 46, 60, 73, and 87. Blood samples were obtained on the same dates. Kilograms of milk produced per cow was measured daily. Body condition score and changes in body condition score were evaluated in relation to daily milk production, cumulative 80-day milk yield, and serum urea nitrogen and cholesterol concentrations. Average daily milk production during week 1 was indicative of cumulative 80-day production, but not of 305-day milk yields. Cows that calved with body condition score greater than or equal to 3.50 did not differ in average daily milk production, cumulative 80-day milk yield, or 305-day milk yield, compared with cows that calved with body condition score less than 3.50. Cows that calved with body condition score greater than or equal to 3.50 lost more condition than did cows that calved with body condition score less than 3.50. Body condition score at calving and amount of body condition loss interacted with the rate of change in daily milk production. Serum urea nitrogen concentration did not differ for cows grouped by cumulative 80-day milk production or for cows grouped by amount of condition loss. Serum cholesterol values were higher than previously reported values and increased directly with milk production. Serum cholesterol values were inversely related to condition loss but changes in cholesterol concentration were not related to condition loss.     

Persistent fecal Salmonella shedding in five dairy herds

OBJECTIVE: To monitor patterns of Salmonella fecal shedding in naturally infected dairy herds, determine the association between fecal shedding and individual animal production measures, and evaluate potential risk factors for shedding of Salmonella organisms among cattle in dairy herds. DESIGN: Longitudinal study. SAMPLE POPULATION: 5 Ohio dairy herds. PROCEDURE: For 3 herds, fecal samples were collected from all mature cows and unweaned calves 7 times during an 18-month period. For the remaining 2 herds, fecal samples were collected from 50 lactating cows 6 times during a 12-month period. Individual animal production records for 3 herds were used to examine associations between individual fecal Salmonella shedding status and 305-day mature-equivalent milk production, somatic cell count, milk fat content, and milk protein content. Multivariable logistic regression was used to test for associations between fecal shedding status and breed, lactation status, lactation number, and duration of lactation. RESULTS: None of the adult animals had clinical signs of salmonellosis, but prevalence of fecal Salmonella shedding at individual collection times ranged from 0 to 99% for cows and from 0 to 67% for unweaned calves. Mature cows were more likely to be shedding Salmonella organisms than were unweaned calves. Within herds, lactation status and duration of lactation for individual animals were associated with Salmonella shedding status. Salmonella fecal shedding status was not associated with individual cow production measures. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that subclinical fecal Salmonella shedding can persist in dairy herds for up to 18 months with no measurable effects on health or production of individual cows.     

Production and related variables in bovine leukaemia virus-infected cows

A newly developed milk dot blot test was used to detect anti-bovine leukaemia virus (BLV) antibody in milk samples from 2079 lactating adult cows from among 61 herds. The milk dot blot test was highly repeatable; the concordance rate, compared with the agar gel immunodiffusion test performed on serum, was 83.5%. All herds contained BLV-positive cows; the prevalence rate was 36%. BLV-positive cows tended to come from larger herds and were older and more often later in lactation. Fourteen production and related variables (herd size, age, days open, days in milk, milk somatic cell count, milk, fat, and protein produced in the current lactation, projected production of milk, fat, and protein, and breed class average deviations for milk, fat, and protein) were compared between BLV-positive and BLV-negative cows. Although somatic cell count, milk produced, and projected production of milk and protein were related significantly to BLV status using simple tests of association, once the variables herd size, age and days in milk were controlled, these differences were removed. Further analyses using logistic (outcome: individual cow BLV status) and least-squares regression (outcome:herd proportion of BLV-positive cows) failed to show an association between any of the measured production or related variables and BLV-positivity. We concluded that the effect of BLV on production and related variables in dairy cows was below the sensitivity of our analytical techniques or was non-existent.Abbreviations ABCA herd average breed class average for milk, fat, and protein production - AVGAGE average age of the herd - ADIM herd average for days in milk - AGID agar gel immunodiffusion - AVGSCC herd average milk somatic cell count - BCA breed class average, a milk, fat and protein production index calculated by comparing a cow's actual 305-day lactation production to the corresponding BCA standard for the same breed, age, and month of calving - BLV bovine leukaemia virus - CALVINT calving interval - COWAGE cow age - DBCA breed class average deviation for milk, fat, and protein production, the difference between an individual cow's BCA and the herd average - DIM days in milk - HS herd size corresponding to the number of lactating cows in a herd - LACT actual amount of milk, fat, and protein produced in a cow's lactation - ODHIC Ontario Dairy Herd Improvement Corporation - PCTPOS percentage of herd that is BLV-positive - PROJ projected 305-day production for milk, fat, and protein by fitting to a standard lactation curve adjusted for days in milk and age at calving - RHBCA rolling herd average for breed class average for milk, fat, and protein production, the average for all cows that completed a lactation (cows must have completed a 305-day lactation) during the previous 12 months - SCC milk somatic cell count     

上海地区荷斯坦牛体型外貌与产奶性状的相关分析

体型外貌性状是奶牛重要的选种指标,是奶牛保持高产、稳产、健康长寿的关键所在。本研究的目的在于探寻上海地区荷斯坦牛体型外貌与产奶性状的相互关系。、随机选取上海市28个奶牛场总计871头第二泌乳期荷斯坦母牛作为研究对象,记录并测定其305d产奶量、乳脂率、乳蛋白率3个产奶性状,体型外貌性状采用9分制评分结果．利用相关分析方法确定体型总分及7个体型外貌性状与各产奶性状之间的关系,结果表明,体型总分与305d产奶量、乳脂率呈极显著正相关（P〈O．01）;体躯容量性状和产奶量呈极显著正相关：肢蹄性状与乳脂率、乳蛋白率呈极显著正相关,与产奶量显著正相关（P〈O．05）;尻部性状与乳脂率呈显著正相关．。最终得出肢蹄、体躯容量、尻部性状是影响荷斯坦牛产奶性状的最主要因素,体型外貌鉴定评分对于筛选高产、优质荷斯坦母牛及选种选配工作具有指导意义。     

Effect of administration of a controlled-release monensin capsule on incidence of calving-related disorders, fertility, and milk yield in dairy cows

OBJECTIVE: To determine the effect of a controlled-release monensin capsule administered at cessation of lactation on incidence of calving-related disorders, fertility, and milk yield in dairy cows. ANIMALS: 290 dairy cows treated with monensin and 290 untreated control cows. PROCEDURE: Treated cows received a capsule that released monensin at 335 mg/d for 95 days. Incidence of calving-related disorders; daily milk yield up to 20 days postpartum; test-day milk yield, fat, protein, and mature-equivalent 305-day milk production; and body condition score at calving were determined. Reproductive variables were conception rate at first service, pregnancy rate, and calving-to-conception interval. RESULTS: Cows treated with monensin were 2.1 times as likely to develop dystocia and 0.8 times as likely to develop metritis as control cows. For milk yield, there was an interaction of treatment X time X parity. In multiparous cows, monensin significantly improved milk yield at test days 4 and 7. In addition, monensin increased body condition score at calving. CONCLUSIONS AND CLINICAL RELEVANCE: Despite increasing the likelihood of developing dystocia and metritis, administration of monensin improved the lactational performance of multiparous cows and may be a promising additive for use at the time of cessation of lactation.     

Risk factors for abomasal displacement in dairy cows.

OBJECTIVE: To determine whether various periparturient events or 305-day milk production during the previous lactation period were associated with abomasal displacement in dairy cows. DESIGN: Retrospective, case-control study. ANIMALS: 75 pairs of case and control cows from 3 university-owned and 3 commercial dairy herds. PROCEDURE: Cows with abomasal displacement were matched with control cows on the basis of herd of origin, breed, age, and calving date. Frequency of specific periparturient events during the period from 2 weeks prior to parturition to diagnosis of abomasal displacement, as well as milk production during the preceding lactation period, were compared between case and control cows. RESULTS: Multivariate analyses indicated that case cows were significantly more likely to have had retained placenta, ketosis, a stillborn calf, metritis, twins, or parturient paresis than were control cows. Dystocia, mastitis, and milk production during the previous lactation period were not associated with abomasal displacement. CLINICAL IMPLICATIONS: Results indicated that a variety of periparturient events were associated with development of abomasal displacement among dairy cows.     

Assessment of test results when using a commercial enzyme-linked immunosorbent assay for diagnosis of paratuberculosis in repeated samples collected from adult dairy cattle

OBJECTIVE: To determine the proportion of adult cattle that change test status when an ELISA for antibodies against Mycobacterium avium subsp paratuberculosis (MAP) is used to assay samples collected twice at variable intervals and to determine whether cows with an initial strong positive result were more likely to maintain positive status, compared with all cows with an initial positive result. DESIGN: Cross-sectional observational study. ANIMALS: 3,757 adult dairy cattle. PROCEDURE: Serum samples were obtained twice from cattle at intervals ranging from 77 to 600 days between collections. Samples were tested with an ELISA for detection of antibodies to MAP. RESULTS: Of 157 cattle with initial positive results (value for the sample divided by the value for positive-control serum [S/P] > or = 0.25), 62 (39.5%) had negative results for the second sample. Of 71 cattle with an initial S/P value > or = 0.40, 13 (18.3%) had a negative result (S/P < 0.25) for the second sample. Of 33 cattle with an initial S/P > or = 0.70, 3 (9.1%) had a negative result (S/P value < 0.25) for the second sample. Interval between collection of samples did not affect results. CONCLUSIONS AND CLINICAL RELEVANCE: Many cows changed ELISA status between samples collected at variable intervals. Cows with an initial high S/P value (> or = 0.70) were more likely to maintain positive status than cows classified as positive on the basis of cutoff values of > or = 0.25 or > or = 0.40. Veterinarians should expect variability in ELISA results when repeated testing of cattle is used as part of an MAP control program.