Shorten P R, Morris C A, Cullen N G
J Anim Sci. 2015 Apr;93(4):1535-45. doi: 10.2527/jas.2014-8490.
The goal was to estimate the heritabilities and genetic variances for pregnancy rate (PR) and calving date (CD) in Angus cattle along with the effect of weight, age, and sire on PR and CD. The data consisted of 4,999 records on PR and CD. Statistical models included year as a fixed effect; premating/postmating weight and age as covariates; and sire of embryo, maternal grandsire (MGS), and permanent maternal environmental effects as random effects. The models also included the interactions between herd and weight (weight change). Direct and maternal effects on PR and CD were estimated using sire MGS and animal models in REML. Pregnancy rate increased from age 2 to 6 and decreased from age 7 to 11 (P < 0.01) and this effect was independent of the culling strategy. There was a quadratic effect of premating cow weight independent of age on PR, with lower PR for low weights (P < 0.01). Overall, cows with a premating weight of 550 kg had the greatest PR. Cows that lost weight during mating had lower PR (P < 0.01). The maternal additive heritability for PR was 0.001 ± 0.012 and the direct additive heritability was 0.024 ± 0.020. The ratio of permanent maternal environmental variance to phenotypic variance was significant (0.048 ± 0.017; P < 0.01). This demonstrates that permanent maternal environmental effects play a major role in the repeatability of PR (0.049 ± 0.015; P < 0.01). The maternal additive heritability for CD was 0.040 ± 0.022, and the direct additive heritability was 0.076 ± 0.045. The ratio of permanent maternal environmental variance to phenotypic variance was low (0.014 ± 0.017) and the repeatability for CD was significant (0.0544 ± 0.0180; P < 0.01). This suggests that maternal genetic effects are as important as direct genetic effects on CD. There was a positive quadratic relationship between premating cow weight and CD with delayed calving for low/high weights (P < 0.01). Cows that lost weight over mating also had a later CD (P < 0.01). Comparisons of a weight-selected herd to the control herd showed differences (P < 0.05) in the optimal premating weight for early calving (control, 480 kg, and weight selected, 615 kg). Calving date was also more sensitive to changes in weight over mating in the weight selection herd (P < 0.05). Therefore, the set point in the weight-fertility axis and the sensitivity of fertility to changes in weight both changed in the weight selection herd.
目标是估计安格斯牛妊娠率（PR）和产犊日期（CD）的遗传力和遗传方差，以及体重、年龄和父系对PR和CD的影响。数据包括4999条关于PR和CD的记录。统计模型将年份作为固定效应；配种前/配种后体重和年龄作为协变量；胚胎父系、母系祖父（MGS）和永久母系环境效应作为随机效应。模型还包括牛群与体重之间的相互作用（体重变化）。使用父系MGS和动物模型在REML中估计对PR和CD的直接和母系效应。妊娠率从2岁到6岁上升，从7岁到11岁下降（P<0.01），且这种效应与淘汰策略无关。配种前母牛体重对PR有独立于年龄的二次效应，体重较低时PR较低（P<0.01）。总体而言，配种前体重为550千克的母牛妊娠率最高。配种期间体重减轻的母牛PR较低（P<0.01）。PR的母系加性遗传力为0.001±0.012，直接加性遗传力为0.024±0.020。永久母系环境方差与表型方差的比率显著（0.048±0.017；P<0.01）。这表明永久母系环境效应在PR的重复性中起主要作用（重复率为0.049±0.015；P<0.01）。CD的母系加性遗传力为0.040±0.022，直接加性遗传力为0.076±0.045。永久母系环境方差与表型方差的比率较低（0.014±0.017），CD的重复性显著（0.0544±0.0180；P<0.01）。这表明母系遗传效应在CD方面与直接遗传效应同样重要。配种前母牛体重与CD之间存在正二次关系，体重过低/过高时产犊延迟（P<0.01）。配种期间体重减轻的母牛产犊日期也较晚（P<0.01）。将一个经过体重选择的牛群与对照牛群进行比较，结果显示在早期产犊的最佳配种前体重方面存在差异（P<0.05）（对照牛群为480千克，体重选择牛群为615千克）。在体重选择牛群中，产犊日期对配种期间体重变化也更敏感（P<0.05）。因此，体重—繁殖力轴上的设定点以及繁殖力对体重变化的敏感性在体重选择牛群中均发生了变化。
