Heat stress negatively impacts the reproductive performance of dairy cows. The main objective of this study was to dissect the genetic basis underlying dairy cow fertility under heat stress conditions. Our first goal was to estimate genetic components of cow conception across lactations considering heat stress. Our second goal was to reveal individual genes and functional gene‐sets that explain a cow’s ability to conceive under thermal stress. Data consisted of 74 221 insemination records on 13 704 Holstein cows. Multitrait linear repeatability test‐day models with random regressions on a function of temperature–humidity index values were used for the analyses. Heritability estimates for cow conception under heat stress were around 2–3%, whereas genetic correlations between general and thermotolerance additive genetic effects were negative and ranged between −0.35 and −0.82, indicating an unfavorable relationship between cows’ ability to conceive under thermo‐neutral vs. thermo‐stress conditions. Whole‐genome scans identified at least six genomic regions on BTA1, BTA10, BTA11, BTA17, BTA21 and BTA23 associated with conception under thermal stress. These regions harbor candidate genes such as BRWD1 , EXD2 , ADAM20 , EPAS1 , TAOK3 , and NOS1 , which are directly implicated in reproductive functions and cellular response to heat stress. The gene‐set enrichment analysis revealed functional terms related to fertilization, developmental biology, heat shock proteins and oxidative stress, among others. Overall, our findings contribute to a better understanding of the genetics underlying the reproductive performance of dairy cattle under heat stress conditions and point out novel genomic strategies for improving thermotolerance and fertility via marker‐assisted breeding.

中文翻译：

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热应激条件下奶牛生殖性能的遗传解剖。

热应激会对奶牛的繁殖性能产生负面影响。这项研究的主要目的是解剖热应激条件下奶牛繁殖力的遗传基础。我们的首要目标是在考虑热应激的情况下估算泌乳期母牛受孕的遗传成分。我们的第二个目标是揭示个体基因和功能基因集，这些基因和功能基因集解释了母牛在热应激条件下受孕的能力。数据由13 704头荷斯坦奶牛的74 221份授精记录组成。使用具有温度-湿度指数值函数的随机回归的多特征线性重复性试验日模型进行分析。在热应激下，牛受胎的遗传力估计约为2-3％，而一般耐性和耐热性加成遗传效应之间的遗传相关性为负，范围在-0.35至-0.82之间，表明母牛在热中性与热应激条件下受孕能力之间的关系不利。全基因组扫描确定了BTA1，BTA10，BTA11，BTA17，BTA21和BTA23上的至少六个基因组区域与受热情况下的受孕有关。这些区域包含候选基因，例如BRWD1，EXD2，ADAM20，EPAS1，TAOK3和NOS1直接与生殖功能和细胞对热应激的反应有关。基因组富集分析揭示了与受精，发育生物学，热激蛋白和氧化应激等相关的功能性术语。总体而言，我们的发现有助于更好地理解热应激条件下奶牛生殖性能的遗传学，并指出了通过标记辅助育种提高耐热性和繁殖力的新基因组策略。