Short communication: Validation of in vitro fertility genes in a Holstein bull population.

Previously, we constructed an in vitro fertilization system for the identification of genes affecting fertility traits in dairy cattle. The efficiency of this system has been demonstrated by the identification of several genes affecting fertilization rate and early embryonic survival. However, to employ these genetic markers in marker- and gene-assisted selection programs, there is a need to validate in vitro results in phenotypic data sets collected in vivo. Thus, the objective of this study was to validate, in a population of Holstein bulls, the fertility trait genes we previously identified in an in vitro system. Estimated relative conception rate (ERCR) data from 222 Holstein bulls were obtained from 5 different artificial insemination companies in the United States. Bulls were genotyped for the genes FGF2, POU1F1, PRL, PRLR, GH, GHR, STAT5A, OPN, and UTMP, and the data were analyzed for association with ERCR using a mixed effects sire model. A stepwise model selection procedure revealed evidence of association with ERCR for FGF2 and STAT5A polymorphisms. The in vivo validation suggests that these genes can be used in gene-assisted selection programs for reproductive performance in dairy cattle. The genotypes found to be associated with low bull fertility in this study have been reported to be associated with high milk composition in previous studies. These findings provide molecular evidence for the antagonistic relationship between milk production and fertility observed for many years in different breeds of dairy cattle.