202 Factors influencing pregnancy loss in lactating dairy cows

Abstract Pregnancy loss in high producing dairy cows is significant and negatively affects profitability of dairy farms. It is not clear the extent of pregnancy loss prior to a subsequent estrus or first pregnancy diagnosis. It is clear that percent of cows losing pregnancies are greatest following 1st pregnancy diagnoses then decrease in a time-related fashion throughout gestation. Non-disease related factors that are associated with pregnancy losses in dairy cows include parity, timing of AI relative to ovulation, circulating concentrations of progesterone during growth of the ovulatory follicle(s), double ovulations, unilateral twins, service sire, extent of change in body condition during early lactation, and serum levels of pregnancy associated glycoproteins at 24 or 28 d post-AI. Metabolic changes related to high milk production resulted in a greater chance for double ovulations. A growing body of literature indicates that cows with unilateral double ovulations and unilateral twins have a greater chance for pregnancy loss during the 1st 90 d of pregnancy compared to cows with single ovulations or bilateral twins. It also appears there is a preferential timing of loss in cows with double vs. single ovulations. Levels of circulating concentrations of progesterone during follicular wave development affect follicular development of cows. In a study that controlled progesterone during follicular development, low levels of progesterone caused a greater percentage of cows to have double ovulations and increased chances for pregnancy loss after 35 d post-AI. Lastly, it appears that cows that lose body condition during the 1st 30 DIM have a greater chance of pregnancy loss between 35 and 69 d post-AI compared with cows that maintained or gained body condition during that period. These data lead towards a greater understanding of the potential causes of pregnancy loss in dairy cows and can be instrumental in the development of reproductive technologies to reduce these losses.