Department of Large Animal Clinical Sciences, Michigan State University, East Lansing 48824, USA.
J Dairy Sci. 2012 Feb;95(2):727-34. doi: 10.3168/jds.2011-4760.
The objective of this study was to determine the herd-level effect of bovine leukemia virus (BLV) infection on dairy production, culling, and cow longevity. During routine herd testing, Dairy Herd Improvement Association technicians collected milk samples from about 40 cows from each of 104 randomly selected Michigan dairy herds averaging ≥120 milking cows and 11,686 kg of milk/yr. Milk samples were analyzed for the presence of anti-BLV antibodies by ELISA, and herd- and lactation-specific estimates of BLV prevalence were computed to determine which were the most predictive of herd milk production, culling rate, and cow longevity (proportion of cows in their third or greater lactation). On this basis, the herd BLV index (an unweighted mean BLV prevalence rate for lactation number 1, 2, 3, and ≥4) was selected as the measure of BLV prevalence that was the most highly associated with BLV economic impact. Step-down multivariate analysis was used to determine the extent to which any of 19 herd-level management variables may have confounded the association of BLV index and measures of herd economic impact (milk production and cow longevity). The BLV index was not associated with the 12-mo culling rate, but was negatively associated in the final multivariable model with the proportion of cows that were ≥third lactation, and was negatively associated with herd milk production. In summary, increased prevalence of BLV within Michigan dairy herds was found to be associated with decreased herd milk production and decreased cow longevity. Our results provide evidence that BLV infection is associated with herd-level economic impacts in high-performing dairy herds.
本研究旨在确定牛白血病病毒 (BLV) 感染对奶牛生产、淘汰和牛寿命的群体效应。在常规的畜群检测中，奶牛群改良协会的技术人员从密歇根州随机选择的 104 个奶牛场中，每个场采集了约 40 头奶牛的奶样，这些奶牛场的平均奶牛存栏数≥120 头，年产奶量≥11686kg。通过 ELISA 分析牛奶样本中抗 BLV 抗体的存在情况，并计算畜群和泌乳特异性 BLV 流行率的估计值，以确定哪些因素最能预测畜群的产奶量、淘汰率和牛寿命（处于第三次或以上泌乳期的奶牛比例）。在此基础上，选择畜群 BLV 指数（泌乳期 1、2、3 和≥4 的未加权平均 BLV 流行率）作为与 BLV 经济影响最相关的 BLV 流行率衡量指标。逐步多元分析用于确定 19 个畜群管理变量中的任何一个变量在多大程度上可能混淆了 BLV 指数与畜群经济影响（产奶量和牛寿命）的相关性。BLV 指数与 12 个月的淘汰率无关，但在最终的多变量模型中，与处于≥第三次泌乳期的奶牛比例呈负相关，与畜群产奶量呈负相关。总之，密歇根州奶牛场中 BLV 流行率的增加与畜群产奶量减少和牛寿命缩短有关。我们的研究结果提供了证据，表明 BLV 感染与高产奶牛场的畜群经济影响有关。
