Evaluating male fertility in Brown Swiss cattle combining multiple sources of information
Improving reproductive performance remains one of the major goals for the dairy industry worldwide. Bull fertility has been recognized as an important factor influencing reproductive success in dairy cattle. In this study, we investigated bull fertility in the Italian Brown Swiss dairy cattle population based on extensive records. The data set included a total of 397,926 breeding records from 1,228 bulls and 129,858 lactating cows between first and fifth lactation from 2000 to 2019, and all bulls have a genomic analysis on 454k single nucleotide polymorphisms (SNP). We estimated sire conception rate using only factors related to the bulls, our analyses revealed that there is a substantial variation in conception rate among Brown Swiss bulls, with more than 20% conception rate difference between high-fertility and low-fertility bulls and cross-validation analyses achieved predictive correlations equal to 0.30 for sire conception rate. The analysis included alternative whole-genome scans and gene-set analyses identified two genomic regions, located on BTA6 and BTA26 that showed marked non-additive effects. These regions harbor genes, such as WDR19 and ADGRA1, that are directly involved in male fertility, including sperm motility, acrosome reaction, and embryonic development. The analysis to evaluate association between ROH and male fertility showed four different ROH regions located on chromosomes 6, 10, 11, and 24 were significantly overrepresented in low-fertility bulls. The predictive performance of the linear kernel-based regression models fitting the entire set of SNP markers exhibited predictive correlations around 0.19. Interestingly, the inclusion of two major non-additive markers as fixed effects achieved predictive correlations around 0.32. Moreover, including in the estimation also a new knowledge on the effect of ROH on the male fertility could improve reliability of prediction.
Key words: Bull fertility, Genomic analysis, Genomic Inbreeding, Brown Swiss cattle
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