Catrett Cassidy C, Moorey Sarah E, Beever Jon E, Rowan Troy N
Department of Animal Science, University of Tennessee, Knoxville, TN 37996, USA.
J Anim Sci. 2024 Jan 3;102. doi: 10.1093/jas/skae364.
Reproduction plays a major role in the production efficiency of livestock species. However, cow-centric reproductive traits tend to be lowly heritable and are not expressed until later in an animal's lifetime, making phenotypic selection alone inefficient at generating genetic gain. Genetic progress can be accelerated by focusing selection on the predicted genetic component of reproductive traits using Expected Progeny Differences. We used the American Simmental Association's performance and Total Herd Enrollment data, made up of 533,155 calving records from 303,158 females (132,403 cows and 170,755 heifers), 33,732 of which are genotyped, to explore three continuous and two discrete phenotypes focused on quantifying early and sustained fertility in beef cows. We analyzed calving date (CD) (cow's CD relative to the start of the calving season), calving interval (CI) (days between calves), first calving interval (FCI) (CI observation between the first and second calving record for a female), heifer pregnancy (HP) (did the animal calve as 2-yr-old), and discrete early calving (DEC) (did animal calve in the first 30 d of the calving season) as distinct, but correlated measures of fertility. This dataset provides insight into population-wide trends related to cow attrition, calving season lengths, and phenotypic variation in fertility. We used pedigree and genomic REML to estimate these six phenotypes' genetic, permanent environment, and temporary environmental variance components. Pedigree-estimated heritabilities were 0.06 (± 0.000011) for CD, (0.04 ± 0.000005) for CI, 0.07 (± 0.000016) for DEC, 0.05 ± 0.000041 for FCI, and 0.23 (± 0.000099) for HP, consistent with other fertility traits across beef and dairy cattle. The incorporation of genomics increased the heritability estimate for HP (0.24 ± 0.000098) and decreased the estimate for FCI (0.04 ± 0.000029). Positive phenotypic and genetic correlations were found among these phenotypes (rG = 0.01 to 0.96). These results call for further work in optimizing genetic predictions and exploration of the genetic architecture through genome-wide studies. Whole herd reporting date frameworks represent opportunities for measuring new reproductive phenotypes, but their utility in genetic evaluations will rely on novel trait initiatives and consistent recording that captures more detailed data.
繁殖在牲畜品种的生产效率中起着重要作用。然而，以母牛为中心的繁殖性状往往遗传力较低，并且直到动物生命后期才会表现出来，这使得仅靠表型选择在产生遗传进展方面效率低下。通过使用预期后代差异将选择重点放在繁殖性状的预测遗传成分上，可以加速遗传进展。我们使用了美国西门塔尔协会的性能和全群登记数据，这些数据由来自303,158头雌性（132,403头母牛和170,755头小母牛）的533,155条产犊记录组成，其中33,732条进行了基因分型，以探索三种连续和两种离散表型，重点是量化肉牛母牛的早期和持续繁殖力。我们分析了产犊日期（CD）（母牛的产犊日期相对于产犊季节开始的时间）、产犊间隔（CI）（犊牛之间的天数）、首次产犊间隔（FCI）（雌性第一次和第二次产犊记录之间的CI观察值）、小母牛妊娠（HP）（该动物在2岁时产犊了吗）以及离散早期产犊（DEC）（动物在产犊季节的前30天内产犊了吗），将它们作为不同但相关的繁殖力指标。该数据集提供了对与母牛淘汰、产犊季节长度和繁殖力表型变异相关的全群体趋势的洞察。我们使用系谱和基因组REML来估计这六种表型的遗传、永久环境和临时环境方差成分。系谱估计的遗传力对于CD为0.06（±0.000011），对于CI为（0.04±0.000005），对于DEC为0.07（±0.000016），对于FCI为0.05±0.000041，对于HP为0.23（±0.000099），与肉牛和奶牛的其他繁殖性状一致。基因组学的纳入提高了HP的遗传力估计值（0.24±0.000098），并降低了FCI的估计值（0.04±0.000029）。在这些表型之间发现了正的表型和遗传相关性（rG = 0.01至0.96）。这些结果呼吁在优化遗传预测和通过全基因组研究探索遗传结构方面开展进一步工作。全群报告日期框架为测量新的繁殖表型提供了机会，但其在遗传评估中的效用将依赖于新的性状倡议和能够捕获更详细数据的一致记录。
