Genetic control of dairy cow reproduction

The decline in dairy cow reproductive performance compromised the productivity and profitability of dairy production worldwide. The phenotypic performance of lactating cows with similar proportions of Holstein genes, similar genetic merit for milk production traits, but either good (Fert+) or poor (Fert-) genetic merit for fertility traits managed in a standardised environment was compared. The objective of this study was to elucidate the physiological mechanisms contributing to suboptimal reproductive performance in lactating dairy cows. Fert+ cows had greater dry matter intake during the first five weeks postpartum, more favourable metabolic status during the transition period, better uterine health during early lactation, were more likely to have resumed cyclicity by week six postpartum, and had greater body condition score and milk production throughout lactation compared with Fert- cows. Preovulatory concentrations of oestradiol, corpus luteum volume and circulating concentrations of progesterone were greater in Fert+ cows compared with Fert- cows during the oestrous cycle. The metabolic clearance rate of progesterone was similar in both genotypes and differences in the hepatic mRNA abundance of genes responsible for progesterone metabolism were minor. Small differences in the abundance of fatty acids and amino acids were detected between genotypes on day seven of the oestrous cycle. Greater abundance of n-6 and total polyunsaturated fatty acids and lesser abundance of saturated fatty acids was observed in the serum of Fert+ cow compared with Fert- cows on day seven of the oestrous cycle. Fatty acid differences in follicular fluid and serum and amino acid differences in follicular fluid were highly predictive of fertility genotype. Combination of transcriptome analysis of the endometrium and corpus luteum on day 13 of the oestrous cycle with genome-wide association studies and whole genome sequence data identified quantitative trait loci regions and putative causal mutations associated with genetic variation in dairy cow fertility. The endometrial expression profile suggested prolonged uterine inflammation, greater prostaglandin F2α synthesis and secretion, and compromised energy status in Fert- cows. The luteal expression profile suggested reduced prostaglandin F2α response, greater steroidogenesis and mRNA processing in Fert+ cows. Collectively, the results highlight the importance of the uterine environment and ovarian activity for the phenotypic fertility differences between genotypes. The study has identified physiological mechanisms controlled by genetic merit for fertility traits that may support reproductive performance without antagonising milk production. This novel lactating cow genetic model of fertility represents a robust and valuable resource for on-going fertility research.