Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis 95616, USA.
J Dairy Sci. 2010 Mar;93(3):1030-40. doi: 10.3168/jds.2009-2611.
The association between Mycobacterium avium ssp. paratuberculosis (MAP) and milk production was estimated on 2 California dairies using longitudinal data from 5,926 cows. Both study herds had moderate MAP seroprevalence, housed cows in freestalls, and had Johne's disease control programs. Cow MAP status was determined using both serum ELISA and fecal culture results from cows tested at dry-off and from whole-herd tests. Potential confounders were evaluated based on a causal diagram. Mixed models with 2 functions (splines) for days in milk (DIM) representing milk production pre- and postpeak used in similar studies were further modified to use each cow's observed DIM at peak and lactation length. Cows that were seropositive produced 2.5kg less 4% fat-corrected milk (FCM) per day than their seronegative herdmates. In addition, cows that were fecal-culture positive by liquid culture and confirmed by PCR produced 2.2kg less 4% FCM per day than their fecal-culture negative herdmates. The decrease in milk production in MAP test-positive compared with test-negative cows started in the second lactation. A switch in MAP status in either ELISA or fecal culture results from positive to negative had no significant association with milk production. Modified DIM functions that used the observed DIM at peak had better model fit than another function that assumed a fixed peak at 60 DIM. Cows that tested positive for MAP on serum ELISA or fecal culture produced less milk than cows that tested negative, and the association between MAP and milk production was not confounded by mastitis, elevated somatic cell counts, or uterine or metabolic cow conditions.
在加利福尼亚的两家奶牛场，使用 5926 头奶牛的纵向数据，评估了鸟分枝杆菌副结核亚种（MAP）与产奶量之间的关系。两个研究牛群的 MAP 血清阳性率均为中等水平，牛群被安置在自由式畜栏中，并且有针对约翰氏病的控制计划。通过在干奶时测试的奶牛的血清 ELISA 和粪便培养结果以及整个牛群的测试结果来确定奶牛的 MAP 状态。基于因果图评估了潜在的混杂因素。使用类似研究中使用的代表产奶量在高峰前和高峰后的牛奶产量的混合模型（样条函数）进一步修改了混合模型，以使用每头奶牛观察到的高峰时的 DIM 和泌乳长度。血清阳性的奶牛比血清阴性的牛群每天少产 2.5 公斤 4%脂肪校正奶（FCM）。此外，通过液体培养阳性并通过 PCR 确认的粪便培养阳性奶牛比粪便培养阴性的牛群每天少产 2.2 公斤 4% FCM。与测试阴性的奶牛相比，MAP 测试阳性的奶牛的产奶量下降始于第二个泌乳期。ELISA 或粪便培养结果从阳性转为阴性的 MAP 状态变化与产奶量没有显著关联。使用观察到的高峰时 DIM 的修改后的 DIM 函数比另一个假设 60DIM 时固定高峰的函数具有更好的模型拟合。在血清 ELISA 或粪便培养中检测到 MAP 阳性的奶牛比检测到 MAP 阴性的奶牛产奶量少，并且 MAP 与产奶量之间的关联不受乳腺炎、体细胞计数升高、子宫或代谢性奶牛状况的混杂。
