Evaluation of the functional role of corpus luteum cavity in recipient selection for bovine embryo transfer.

Abstract

Objective: The success of bovine embryo transfer (ET) programs largely depends on selecting optimal recipient cows, with a functional corpus luteum (CL) playing a critical role in the maintenance of pregnancy. While CL size and blood perfusion (CLBP) have been extensively studied, the presence of CL cavities (CLcav) and their impact on fertility remain controversial. This study aimed to assess the functional significance of CLcav in the selection of recipients for ET by evaluating its association with pregnancy outcomes, CLBP, and hormonal profiles.

Methods: Ninety-eight Hanwoo cows underwent estrus synchronization and transrectal ultrasonographic evaluation. Eighty-five recipients were selected based on CL diameter (≥15 mm) and the absence of large dominant follicles (≥10 mm). CL type (compact vs. cavitary), CLBP (color Doppler), and hormone levels (estradiol (E2) and progesterone (P4)) were recorded on Day 6.5 post-estrus. ET was performed using in vitro-produced fresh or vitrified embryos, and pregnancy status was assessed 40-60 days post-transfer.

Results: CLcav was detected in 18.8% of recipients, but pregnancy rates did not significantly differ between cows with and without CLcav (50.0% vs. 62.3%, p > 0.05). However, when CLcav occupied ≥40% of the CL volume (CLcav diameter 18mm or less), conception rates increased (62.5% vs. 37.5%), alongside elevated E2 levels. When CLBP was 40% or higher, CLcav size and P4 concentration were the highest, but excessive CLBP did not enhance conception rates.

Conclusion: These findings suggest that CLcav does not impair luteal function or pregnancy outcomes and may, in some cases, indicate enhanced luteal activity. Integrating CL morphology, vascularization, and hormonal balance into recipient selection criteria may improve ET efficiency. Future studies should further investigate the physiological mechanisms underlying CLcav formation and its role in reproductive success.