Department of Ruminant Science, Institute of Animal Sciences, Agricultural Research Organization, the Volcani Center, Rishon LeZion 7505101, Israel.
Israeli Cattle Breeders Association, Caesarea Industrial Park 3088900, Israel.
J Dairy Sci. 2020 May;103(5):4495-4509. doi: 10.3168/jds.2019-17482. Epub 2020 Feb 26.
One of the causes of observed low fertility is embryo loss after fertilization. Previous findings suggested that more than half of fertilizations result in embryo loss before pregnancy is detected. We proposed reinsemination between 49 and 100 d after the first insemination as an indicator trait for early abortion (EA) in dairy cattle based on the mean estrus interval of 21 d. This trait was compared with conception rate from first insemination and conception status, computed as the inverse of the number of inseminations to conception. Animal model variance components were estimated by REML, including parents and grandparents of cows with records. First-parity heritability for first insemination conception rate was 3%. In the multitrait analysis of parities 1 to 3 for putative EA, heritabilities ranged from 8.9% for first parity to 10.4% for second parity. All genetic correlations were >0.9, whereas all environmental correlations were <0.12. The variance component for the service sire effect for putative EA rate was less than half the variance component for conception rate. Thus, genetic control of the 2 traits is clearly different, and analysis of EA rate by a single-trait animal model is justified. Genetic evaluation for putative EA was computed using this model, including all first- through third-parity cows with freshening dates from January 1, 1985, through December 31, 2016, that either became pregnant on first insemination or were reinseminated between 49 and 100 d after the first insemination. All known parents and grandparents of cows with records were included in the analysis. The regression of the breeding value for non-abortion rate on the cows' birth year was 0.083%/yr. The genetic correlation between first-parity EA and conception status was 0.995. The genetic correlations between first-parity EA and milk, fat, and protein production were all negative, whereas the genetic correlation between EA and herd life was 0.33. Inclusion of putative EA in the selection index instead of conception status resulted in 10 to 20% greater genetic gain for both fertility traits. In a genome-wide association study based on 1,200 dairy bulls with reliabilities >50% for abortion rate genotyped for 41,000 markers, 6 markers were found with nominal probabilities of <10 to reject the null hypothesis of no effect on EA rate. The markers with the lowest probabilities for EA rate were also included among the markers with the lowest probabilities for female fertility, but not vice versa. The marker explaining the most variance for abortion rate is located within the ABCA9 gene, which is found within an ATP-binding cassette (ABC) genes cluster. The ABC family is the major class of primary active transporters in the placenta.
受精后胚胎丢失是观察到的低生育率的原因之一。先前的研究结果表明，超过一半的受精会导致胚胎丢失，直到怀孕被检测到。我们提出在第一次授精后 49 到 100 天之间重新授精，作为奶牛早期流产（EA）的指示性状，这是基于平均发情间隔 21 天。该性状与首次授精的妊娠率和妊娠状态进行比较，妊娠状态计算为受孕所需授精次数的倒数。通过 REML 估计动物模型方差分量，包括有记录的牛的父母和祖父母。首次授精妊娠率的第一胎遗传力为 3%。在针对潜在 EA 的第 1 至第 3 胎的多性状分析中，遗传力范围从第一胎的 8.9%到第二胎的 10.4%。所有遗传相关系数均大于 0.9，而所有环境相关系数均小于 0.12。潜在 EA 率的授精种公牛效应的方差分量小于妊娠率的方差分量的一半。因此，这两个性状的遗传控制显然不同，并且通过单一性状动物模型分析潜在 EA 率是合理的。使用该模型对潜在 EA 进行遗传评估，包括所有初次至第三次配种的奶牛，其产犊日期为 1985 年 1 月 1 日至 2016 年 12 月 31 日，要么在首次授精时怀孕，要么在首次授精后 49 至 100 天之间重新授精。所有有记录的牛的已知父母和祖父母都包括在分析中。非流产率的育种值与牛的出生年份的回归为 0.083%/年。第一胎 EA 与妊娠状态的遗传相关系数为 0.995。第一胎 EA 与牛奶、脂肪和蛋白质产量的遗传相关系数均为负，而 EA 与畜群寿命的遗传相关系数为 0.33。将潜在的 EA 纳入选择指数而不是妊娠状态，会使这两个生育性状的遗传增益提高 10%至 20%。在一项基于 1200 头公牛的全基因组关联研究中，这些公牛的流产率可靠性 >50%，并对 41000 个标记进行了基因分型，发现有 6 个标记的概率小于 10%，可以拒绝对 EA 率没有影响的零假设。与 EA 率的最低概率相关的标记也包括在与雌性生育力的最低概率相关的标记中，但反之则不然。解释流产率变异最大的标记位于 ABCA9 基因内，该基因位于 ATP 结合盒（ABC）基因簇内。ABC 家族是胎盘内主要的初级主动转运蛋白家族。
