Heat stress and fescue toxicosis caused by ingesting tall fescue infected with the endophytic fungus Epichloë coenophiala represent two of the most prevalent stressors to beef cattle in the United States and cost the beef industry millions of dollars each year. The rate at which a beef cow sheds her winter coat early in the summer is an indicator of adaptation to heat and an economically relevant trait in temperate or subtropical parts of the world. Furthermore, research suggests that early-summer hair shedding may reflect tolerance to fescue toxicosis, since vasoconstriction induced by fescue toxicosis limits the ability of an animal to shed its winter coat. Both heat stress and fescue toxicosis reduce profitability partly via indirect maternal effects on calf weaning weight. Here, we developed parameters for routine genetic evaluation of hair shedding score in American Angus cattle, and identified genomic loci associated with variation in hair shedding score via genome-wide association analysis (GWAA). Hair shedding score was moderately heritable (h2 = 0.34 to 0.40), with different repeatability estimates between cattle grazing versus not grazing endophyte-infected tall fescue. Our results suggest modestly negative genetic and phenotypic correlations between a dam’s hair shedding score (lower score is earlier shedding) and the weaning weight of her calf, which is one metric of performance. Together, these results indicate that economic gains can be made by using hair shedding score breeding values to select for heat-tolerant cattle. GWAA identified 176 variants significant at FDR < 0.05. Functional enrichment analyses using genes that were located within 50 kb of these variants identified pathways involved in keratin formation, prolactin signalling, host-virus interaction, and other biological processes. This work contributes to a continuing trend in the development of genetic evaluations for environmental adaptation. Our results will aid beef cattle producers in selecting more sustainable and climate-adapted cattle, as well as enable the development of similar routine genetic evaluations in other breeds.

中文翻译：

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开发美国安格斯牛脱毛遗传评估以提高耐热性

摄入感染内生真菌 Epichloë coenophiala 的高羊茅引起的热应激和羊茅中毒是美国肉牛面临的两种最普遍的应激源，每年给牛肉行业造成数百万美元的损失。肉牛在夏初脱掉冬季皮毛的速度是适应炎热的指标，也是世界温带或亚热带地区经济相关的特征。此外，研究表明，初夏脱毛可能反映了对羊茅中毒的耐受性，因为羊茅中毒引起的血管收缩限制了动物脱去冬季皮毛的能力。热应激和羊茅中毒都会降低盈利能力，部分原因是母体对犊牛断奶体重的间接影响。在这里，我们开发了美国安格斯牛脱毛评分的常规遗传评估参数，并通过全基因组关联分析（GWAA）确定了与脱毛评分变异相关的基因组位点。脱毛评分具有中等遗传性（h2 = 0.34 至 0.40），放牧与不放牧感染内生菌的高羊茅之间的重复性估计不同。我们的结果表明，母马的脱毛分数（分数越低表示脱毛越早）与小牛的断奶体重（性能指标之一）之间存在适度的负遗传和表型相关性。总之，这些结果表明，通过使用脱毛评分育种值来选择耐热牛可以获得经济收益。GWAA 识别出 176 个 FDR < 0.05 时显着的变异。使用位于这些变体 50 kb 范围内的基因进行功能富集分析，确定了参与角蛋白形成、催乳素信号传导、宿主-病毒相互作用和其他生物过程的途径。这项工作有助于环境适应遗传评估发展的持续趋势。我们的结果将帮助肉牛生产者选择更可持续和更适应气候的牛，并有助于在其他品种中开发类似的常规遗传评估。