Department of Large Animal Sciences, University of Copenhagen, 1870 Frederiksberg C, Denmark.
J Dairy Sci. 2010 Jan;93(1):304-10. doi: 10.3168/jds.2009-2528.
Salmonella enterica ssp. enterica Dublin is the most common Salmonella serotype found in the dairy sector in Denmark. Salmonella antibody level in bulk-tank milk (BTM), indicative of Salmonella Dublin infection in the herd, has been recorded regularly in all Danish dairy herds through a surveillance program since 2002. The objective of this study was to investigate whether high BTM Salmonella antibody level was associated with high calf mortality at herd level. Other risk factors for high calf mortality were also investigated: breed, production type (organic vs. conventional), number of animals purchased, herd size, and number of neighbor herds within a 4.9-km radius. Data from the Danish Cattle Database including the Salmonella surveillance program from September 2007 through August 2008 were used. Dairy herds with more than 20 cows were included (n=4,337). Because of a highly right-skewed distribution of calf mortality with many zero values, calf mortality had to be dichotomized for the analysis. Therefore, in this study, high calf mortality was defined as calf mortality of more than 6.5% for calves aged 1 to 180 d. A logistic analysis was performed to identify risk factors associated with the probability of a herd having high calf mortality. The following factors were significantly associated with high calf mortality: high BTM Salmonella antibody level, odds ratio (OR)=2.0 (95% confidence interval=1.6-2.4), organic production OR=1.4 (95% confidence interval=1.1-1.7) for organic versus conventional production, and breed. Purchase of 8 or more animals increased the OR of high calf mortality more than purchase of 1 to 7 animals, which again had a higher OR compared with purchase of 0 animals. Because only 14.3% of the population consisted of herds with high BTM Salmonella status, the estimated proportion of herds with high calf mortality could only be reduced from 38.7 to 36.5% by eradicating Salmonella from the Danish cattle population (i.e., a population attributable risk of 2.2%). This showed that although there is a strong association between BTM Salmonella status and calf mortality, the problem with high calf mortality will not be solved by eradicating Salmonella. All other things equal, a population with more Salmonella-infected herds would gain a larger reduction in calf mortality from a Salmonella control campaign. Nevertheless, individual herds with a high within-herd prevalence of Salmonella are likely to benefit, both economically and regarding animal welfare, from controlling pathogenic Salmonella types in cattle.
都柏林沙门氏菌亚种是丹麦乳制品行业最常见的沙门氏菌血清型。自 2002 年以来，丹麦所有奶牛场都通过一项监测计划定期记录牛奶大罐（BTM）中的沙门氏菌抗体水平，以反映牛群中是否存在都柏林沙门氏菌感染。本研究旨在调查 BTM 中高浓度的沙门氏菌抗体水平是否与牛群高水平的犊牛死亡率有关。还调查了其他导致高水平犊牛死亡率的风险因素：品种、生产类型（有机与传统）、购买的动物数量、牛群规模以及 4.9 公里半径范围内的相邻牛群数量。本研究使用了丹麦奶牛数据库的数据，包括 2007 年 9 月至 2008 年 8 月的沙门氏菌监测计划。本研究纳入了奶牛场中奶牛数量超过 20 头的牛群（n=4337）。由于犊牛死亡率存在严重的右偏分布，且有许多零值，因此必须对其进行二分类分析。因此，在本研究中，高死亡率被定义为 1-180 日龄犊牛死亡率超过 6.5%。采用逻辑回归分析确定与牛群高死亡率相关的风险因素。结果表明，以下因素与高死亡率显著相关：BTM 中高浓度的沙门氏菌抗体水平（比值比[OR]为 2.0，95%置信区间[CI]为 1.6-2.4）、有机生产（OR 为 1.4，95% CI 为 1.1-1.7）与传统生产相比，以及品种。与购买 0 只动物相比，购买 1-7 只动物和 8 只或更多动物会增加犊牛死亡率高的可能性，后两者的 OR 更高。由于只有 14.3%的人群由具有高 BTM 沙门氏菌状态的牛群组成，因此通过从丹麦牛群中根除沙门氏菌（即归因风险为 2.2%），高死亡率牛群的估计比例只能从 38.7%降低到 36.5%。这表明，尽管 BTM 中沙门氏菌状态与犊牛死亡率之间存在很强的关联，但通过根除沙门氏菌并不能解决高死亡率的问题。在所有其他条件相同的情况下，一个具有更多感染沙门氏菌的牛群的人群将从沙门氏菌控制运动中获得更大的犊牛死亡率降低。然而，具有高群体内沙门氏菌流行率的单个牛群可能会从控制牛群中的致病性沙门氏菌类型中受益，无论是在经济上还是在动物福利方面。
