Moorepark Production Research Centre, Fermoy, Co. Cork, Ireland.
J Dairy Sci. 2010 Nov;93(11):5413-22. doi: 10.3168/jds.2009-2925.
Mycobacterium bovis is the primary agent of tuberculosis (TB) in cattle. The failure of Ireland and some other countries to reach TB-free status indicates a need to investigate complementary control strategies. One such approach would be genetic selection for increased resistance to TB. Previous research has shown that considerable genetic variation exists for susceptibility to the measures of M. bovis infection, confirmed M. bovis infection, and M. bovis-purified protein derivative (PPD) responsiveness. The objective of this study was to estimate the genetic and phenotypic correlations between economically important traits and these measures of M. bovis infection. A total of 20,148 and 17,178 cows with confirmed M. bovis infection and M. bovis-PPD responsiveness records, respectively, were available for inclusion in the analysis. First- to third-parity milk, fat, and protein yields, somatic cell count, calving interval, and survival, as well as first-parity body condition score records, were available on cows that calved between 1985 and 2007. Bivariate linear-linear and threshold-linear sire mixed models were used to estimate (co)variance components. The genetic correlations between economically important traits and the measures of M. bovis infection estimated from the linear-linear and threshold-linear sire models were similar. The genetic correlations between susceptibility to confirmed M. bovis infection and economically important traits investigated in this study were all close to zero. Mycobacterium bovis-PPD responsiveness was positively genetically correlated with fat production (0.39) and body condition score (0.36), and negatively correlated with somatic cell score (-0.34) and survival (-0.62). Hence, selection for increased survival may indirectly reduce susceptibility to M. bovis infection, whereas selection for reduced somatic cell count and increased fat production and body condition score may increase susceptibility to M. bovis infection.
牛分枝杆菌是牛结核病（TB）的主要病原体。爱尔兰和其他一些国家未能达到无结核病状态，这表明需要调查补充控制策略。一种方法是遗传选择以提高对结核病的抵抗力。先前的研究表明，对牛分枝杆菌感染的度量、确诊的牛分枝杆菌感染以及牛分枝杆菌纯化蛋白衍生物（PPD）反应性存在相当大的遗传变异。本研究的目的是估计与这些牛分枝杆菌感染度量相关的经济重要性状的遗传和表型相关性。共有 20148 头和 17178 头母牛分别具有确诊的牛分枝杆菌感染和牛分枝杆菌-PPD 反应记录，可用于分析。1985 年至 2007 年期间产犊的母牛具有第一至第三胎泌乳、脂肪和蛋白质产量、体细胞计数、产犊间隔和存活率，以及第一胎体况评分记录。使用双变量线性-线性和阈值线性 sire 混合模型来估计（协）方差分量。线性-线性和阈值线性 sire 模型估计的经济重要性状与牛分枝杆菌感染度量之间的遗传相关性相似。本研究中调查的对确诊的牛分枝杆菌感染的易感性与经济重要性状之间的遗传相关性均接近零。牛分枝杆菌-PPD 反应性与脂肪产量（0.39）和体况评分（0.36）呈正遗传相关，与体细胞评分（-0.34）和存活率（-0.62）呈负遗传相关。因此，选择提高存活率可能会间接降低对牛分枝杆菌感染的易感性，而选择降低体细胞计数、增加脂肪产量和体况评分可能会增加对牛分枝杆菌感染的易感性。
