Evaluating impact of season and corpus luteum cavitation on serum progesterone concentration and pregnancy in a Holstein dairy herd

Abstract

The corpus luteum (CL) is vital to bovine reproduction and can present in 2 forms on ultrasound examination: homoge­neous or cavitary. Impact of CL cavitation on fertility in cattle has been debated. Many variables influence fertility includ­ing heat stress, but little is known regarding the impact of season and risk of association with a cavitary CL. The objec­tives of this study were to evaluate: (1) effect of CL form on serum progesterone, and (2) effect of reproductive status and season on the likelihood of diagnosing a cavitary CL. Blood from Holstein cows (n = 787) on a commercial dairy farm was collected (n = 1,062) at 39-45 days post-insemination. Some cows were sampled more than once. Corpora lutea were categorized as homogeneous or cavitary, and cows were diagnosed as either pregnant or non-pregnant via transrectal ultrasonography at time of blood collection. When adjusted for season and CL status, pregnant cows produced higher serum progesterone (6.880 ng/mL; 95% CI [6.606, 7.153]) than non-pregnant cows (4.664 ng/mL; 95% CI [4.398, 4.931], P < 0.001). When adjusted for progesterone levels and season, pregnant cows were 94.7% less likely (OR = 0.053, P < 0.001) to be diagnosed with a cavitary CL com­pared to non-pregnant cows. No difference was observed in serum progesterone by CL form (P = 0.393). Serum progester­one was significantly lower in summer than fall (P < 0.001), winter (P < 0.001) and spring (P = 0.005). Season did not impact likelihood of diagnosing a cavitary CL.