University of Missouri, Columbia, MO, 65211, USA.
Angus Genetics Inc., St. Joseph, MO, 64506, USA.
Genet Sel Evol. 2020 Oct 21;52(1):63. doi: 10.1186/s12711-020-00584-0.
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 (h = 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.
美国的肉牛面临着两大主要应激源，一是由内生真菌 Epichloë coenophiala 感染的高羊茅引起的热应激，二是采食高羊茅后的中毒症。这两种应激源每年给肉牛产业造成了数百万美元的损失。肉牛在初夏提前褪去冬毛的速度是其适应热应激的一个指标，在温带或亚热带地区，这也是一个具有经济意义的性状。此外，研究表明，初夏毛发脱落可能反映了对毒草中毒的耐受性，因为毒草中毒引起的血管收缩限制了动物褪去冬毛的能力。热应激和毒草中毒都会通过对犊牛断奶体重的间接母体效应降低盈利能力。在这里，我们开发了美国安格斯牛毛发脱落评分常规遗传评估的参数，并通过全基因组关联分析（GWAA）确定了与毛发脱落评分变异相关的基因组位点。
毛发脱落评分具有中度的遗传力（h=0.34 至 0.40），在放牧和不放牧内生菌感染高羊茅的牛群之间存在不同的可重复性估计。我们的结果表明，母畜的毛发脱落评分（评分越低，脱落越早）与其犊牛的断奶体重之间存在适度的负遗传和表型相关，这是衡量性能的一个指标。综上所述，利用毛发脱落评分的育种值选择耐热牛，可以获得经济效益。GWAA 鉴定出 176 个在 FDR<0.05 水平下显著的变异。对位于这些变异体 50kb 以内的基因进行功能富集分析，确定了与角蛋白形成、催乳素信号转导、宿主-病毒相互作用和其他生物学过程相关的途径。
这项工作是开发环境适应遗传评估的持续趋势的一部分。我们的研究结果将有助于肉牛生产者选择更可持续和适应气候变化的牛，并且能够在其他品种中开发类似的常规遗传评估。
