mRNA of luteal genes associated with progesterone synthesis, maintenance, and apoptosis in dairy heifers and lactating dairy cows.

This study was performed to investigate the role of corpus luteum (CL) in reduced pregnancy rates (PR) observed in high producing lactating dairy cows. Development of CL and secretion of progesterone (P(4)) play a key role in early embryo development, implantation, and maintenance of pregnancy. Time of ovulation was synchronized in dairy heifers and second/third parity lactating dairy cows and CL enucleated surgically under local anesthesia on day 10 of the estrous cycle. Quality of the CL in dairy heifers (n=5) and lactating dairy cows (n=5) was compared by analyzing the expression of candidate genes by mRNA assessments using quantitative real-time PCR. Amounts of mRNA for factors associated with P(4) synthesis: 3betaHSD, anti-apoptotic function: BCL2, angiogenesis: VEGF, IGF1, and FGF2, and luteal maintenance: IL1A were greater (P<0.05) in CL obtained from dairy heifers compared to that of lactating dairy cows. Also a greater ratio for BAX:BCL2 mRNA was observed in lactating cows. Therefore, genes regulating angiogenic, steroidogenic, and luteotropic factors are highly expressed in heifers compared to lactating dairy cows, whereas apoptosis seemed to be more evident in CL of lactating cows. These findings suggest that CL of lactating dairy cows have reduced luteotropic as well as steroidogenic capacities on day 10 of the estrous cycle and might have played a critical role in reduced PR observed in lactating dairy cows.