Phenotypic performances of livestock animals decline with increasing levels of inbreeding, however, the noticeable decline known as inbreeding depression, may not be due only to the total level of inbreeding, but rather could be distinctly associated with more recent or more ancient inbreeding. Therefore, splitting inbreeding into different age classes could help in assessing detrimental effects of different ages of inbreeding. Hence, this study sought to investigate the effect of recent and ancient inbreeding on production and fertility traits in Canadian Holstein cattle with both pedigree and genomic records. Furthermore, inbreeding coefficients were estimated using traditional pedigree measure (FPED) and genomic measures using segment based (FROH) and marker-by-marker (FGRM) based approaches. Inbreeding depression was found for all production and most fertility traits, for example, every 1% increase in FPED, FROH and FGRM was observed to cause a − 44.71, − 40.48 and − 48.72 kg reduction in 305-day milk yield (MY), respectively. Similarly, an extension in first service to conception (FSTC) of 0.29, 0.24 and 0.31 day in heifers was found for every 1% increase in FPED, FROH and FGRM, respectively. Fertility traits that did not show significant depression were observed to move in an unfavorable direction over time. Splitting both pedigree and genomic inbreeding into age classes resulted in recent age classes showing more detrimental inbreeding effects, while more distant age classes caused more favorable effects. For example, a − 1.56 kg loss in 305-day protein yield (PY) was observed for every 1% increase in the most recent pedigree age class, whereas a 1.33 kg gain was found per 1% increase in the most distant pedigree age class. Inbreeding depression was observed for production and fertility traits. In general, recent inbreeding had unfavorable effects, while ancestral inbreeding had favorable effects. Given that more negative effects were estimated from recent inbreeding when compared to ancient inbreeding suggests that recent inbreeding should be the primary focus of selection programs. Also, further work to identify specific recent homozygous regions negatively associated with phenotypic traits could be investigated.

中文翻译：

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最近和近交对加拿大荷斯坦牛的生产和生育性状的影响。

随着近亲繁殖水平的提高，家畜的表型表现下降，但是，被称为近亲繁殖抑郁的明显下降，可能不仅是由于近亲繁殖的总水平，而且还可能与较新或更近的近亲繁殖明显相关。因此，将近交分为不同的年龄类别可以帮助评估不同近交年龄的有害影响。因此，本研究试图通过谱系和基因组记录来调查最近和近交对加拿大荷斯坦牛的生产和生育性状的影响。此外，近亲繁殖系数是使用传统的谱系测度（FPED）估算的，而基因组测量是使用基于片段的（FROH）和基于逐个标记（FGRM）的方法进行估算的。发现所有生产和大多数生育性状的近交衰退，例如，观察到FPED，FROH和FGRM每增加1％，导致305天的产奶量（MY）降低− 44.71，− 40.48和− 48.72 kg，分别。同样，在小母牛中，每增加1％的FPED，FROH和FGRM，首次怀孕至受孕（FSTC）的时间就会延长0.29、0.24和0.31天。随着时间的推移，未显示出明显抑郁的生育力特征会朝不利的方向发展。将谱系和基因组近交分为年龄段，导致最近的年龄段显示出更多的有害近交效应，而更远的年龄段则产生更有利的效应。例如-1。在最新的谱系年龄组中，每增加1％，则305天蛋白质产量（PY）减少56公斤，而在最远的谱系年龄组中，每增加1％，则增加1.33公斤。观察到近亲抑郁的生产和生育特征。总的来说，最近的近亲繁殖有不利影响，而祖先近亲繁殖有有利影响。鉴于与近亲繁殖相比，近亲繁殖带来的负面影响更大，这表明近亲繁殖应成为选择计划的主要重点。同样，可以进行进一步的工作以鉴定与表型性状负相关的最近的纯合子区域。观察到近亲抑郁的生产和生育特征。总的来说，最近的近亲繁殖有不利影响，而祖传近亲繁殖有有利影响。鉴于与近亲繁殖相比，近亲繁殖带来的负面影响更大，这表明近亲繁殖应成为选择计划的主要重点。同样，可以进行进一步的工作以鉴定与表型性状负相关的最近的纯合子区域。观察到近亲抑郁的生产和生育特征。总的来说，最近的近亲繁殖有不利影响，而祖先近亲繁殖有有利影响。鉴于与近亲繁殖相比，近亲繁殖带来的负面影响更大，这表明近亲繁殖应成为选择计划的主要重点。同样，可以进行进一步的工作以鉴定与表型性状负相关的最近的纯合子区域。