Genetic improvement in cattle—are we sacrificing reproduction in favor of production?

Abstract

Reproductive traits can range from lowly to moderately heritable. Genomic technologies provide a powerful tool for improving selection for traits that are lowly heritable, sex-linked, or not expressed until later in life. Therefore, as genomic technologies become a part of selection decisions, there is a critical need to understand how specific gene variants affect reproductive traits in cattle. Both classical quantitative genetics approaches and genomic approaches have identified genetic correlations between production traits and fertility. In dairy cows, single trait selection for milk production and associated inbreeding has resulted in a decline in conception rates over the last 60 years. Conversely, increases in body condition score at the time of calving in both beef and dairy cows are advantageously genetically correlated with decreased postpartum intervals to estrus. In beef cattle, the allele of µ-calpain (CAPN1) associated with increased meat tenderness is also associated with an increased postpartum interval to ovulation that could be detrimental to reproductive performance in the cow herd. However, in Charolais cattle, there was no genetic correlation between ovarian activity in females and proportion of adipose tissue in male carcasses, indicating that carcass traits can be improved without negatively impacting reproduction in the cow herd when selection is applied properly. Thus, there is a need for a systems based approach to understand how specific gene variants influence the overall physiology to ensure that selection pressure is applied uniformly for production, disease resistance, heat tolerance, and parasite resistance without negatively impacting reproductive efficiency in the cow herd.