Abstract Excellent reproductive performance (i.e. 365-day calving interval) is paramount to herd profit in seasonal-calving dairy systems. Reproductive targets are currently not being achieved in Irish dairy herds. Furthermore, most research on the genetics of reproductive performance in dairy cattle has focused primarily on lactating cows and relatively few studies have attempted to quantify the genetic contribution to differences in reproductive performance in nulliparae. The objective of the present study was to estimate the contribution of both the additive and non-additive genetic components, as well as the permanent environmental component, to phenotypic variation in the reproductive traits in nulliparous, primiparous and multiparous seasonal-calving dairy females. Reproductive phenotypes were available on up to 202,525 dairy females. Variance components were estimated using (repeatability where appropriate) linear animal mixed models; fixed effects included in the mixed models were contemporary group, parity (where appropriate), breed proportion, inter-breed specific heterosis coefficients and inter-breed specific recombination loss coefficients. Heritability of the reproductive traits ranged from 0.004 (pregnancy rate to first service) to 0.17 (age at first service in nulliparae), while repeatability estimates for the reproductive traits in cows ranged from 0.01 (calving interval) to 0.11 (pregnant in the first 42 days of the breeding season). Breed-specific heterosis regression coefficients suggest that, relative to the parental mean, a first-cross Holstein–Jersey crossbred was almost 7 days younger at first calving, had a 9-day shorter calving interval, a 6 percentage unit greater pregnancy rate in the first 42 days of the breeding season and a 3 percentage unit greater survival rate to next lactation. Heifer calving rate traits were strongly genetically correlated with age at first calving (–0.97 to –0.66) and calving rate in the first 42 days of the calving season for first parity cows (0.77 to 0.56), but genetic correlations with other cow reproductive traits were weak and inconsistent. Calving interval was strongly genetically correlated with the majority of the cow traits; 56%, 40%, and 92% of the genetic variation in calving interval was explained by calving to the first service interval, number of services and pregnant in the first 42 days of the breeding season, respectively. Permanent environmental correlations between the reproductive performance traits were generally moderate to strong. The existence of contributions from non-additive genetic and permanent environmental effects to phenotypic differences among cows suggests the usefulness of such information to rank cows on future expected performance; this was evidenced by a stronger correlation with future reproductive performance for an individual cow index that combined additive genetic, non-additive genetic and permanent environmental effects compared to an index based solely on additive genetic effects (i.e. estimated breeding values).

中文翻译：

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加性遗传、非加性遗传和永久性环境对季节性产犊奶牛雌性生殖性能的影响

摘要 在季节性产犊奶牛系统中，出色的繁殖性能（即 365 天的产犊间隔）对畜群利润至关重要。爱尔兰奶牛群目前尚未实现生殖目标。此外，大多数关于奶牛繁殖性能遗传学的研究主要集中在泌乳奶牛上，相对较少的研究试图量化对未产妇繁殖性能差异的遗传贡献。本研究的目的是估计加性和非加性遗传成分以及永久性环境成分对初产、初产和经产季节性产犊奶牛生殖性状表型变异的贡献。多达 202,525 头奶牛的生殖表型可用。使用（适当时可重复性）线性动物混合模型估计方差分量；混合模型中包含的固定效应是当代群体、胎次（在适当情况下）、品种比例、品种间特定杂种优势系数和品种间特定重组损失系数。繁殖性状的遗传力范围为 0.004（首次分娩的妊娠率）至 0.17（初产初龄），而奶牛繁殖性状的可重复性估计范围为 0.01（产犊间隔）至 0.11（前 42 次妊娠）繁殖季节的天数）。品种特异性杂种优势回归系数表明，相对于亲本平均值，首次杂交的荷斯坦-泽西杂交种在第一次产犊时几乎年轻了 7 天，产犊间隔缩短了 9 天，在繁殖季节的前 42 天，妊娠率提高 6 个单位，到下一个泌乳期的存活率提高 3 个单位。小母牛产犊率性状与第一次产犊年龄（–0.97 至 –0.66）和第一胎母牛产犊季节前 42 天的产犊率（0.77 至 0.56）有很强的遗传相关性，但与其他奶牛繁殖性状的遗传相关性是软弱和不一致的。产犊间隔与大多数奶牛性状有很强的遗传相关性；56%、40%和92%的产犊间隔遗传变异分别由产犊至第一个配种间隔、配种数和繁殖季节前42天的怀孕来解释。繁殖性能特征之间的永久性环境相关性通常为中度至强。非加性遗传和永久性环境影响对奶牛表型差异的影响的存在表明，此类信息可用于对奶牛未来预期性能进行排名；与仅基于加性遗传效应（即估计育种值）的指数相比，结合加性遗传、非加性遗传和永久性环境影响的个体奶牛指数与未来繁殖性能的相关性更强，证明了这一点。