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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.
DiPastina et al. (Thu,) studied this question.