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

## TL;DR

This study examines whether the presence of a corpus luteum cavity in cows affects the success of embryo transfer, finding it does not hinder pregnancy outcomes and may even indicate better luteal function.

## Contribution

The study provides new insights into the functional role of corpus luteum cavities in bovine embryo transfer recipient selection.

## Key findings

- CLcav presence did not significantly affect pregnancy rates in recipient cows.
- Larger CLcav size (≥40% of CL volume) was associated with improved conception rates and higher estradiol levels.
- High CL blood perfusion levels did not further improve conception rates despite peak P4 and CLcav size.

## Abstract

The effectiveness of bovine embryo transfer (ET) programs is significantly influenced by selection of optimal recipient cows, in which a functional corpus luteum (CL) is critical for the maintenance of pregnancy. The relationship between CL size and blood perfusion (CLBP) has been extensively studied; however, the implications of CL cavities (CLcav) 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.

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

CLcav identified in 18.8% of recipients, but pregnancy rates were not significantly different between cows with and without CLcav (50.0% vs. 62.3%, p>0.05). When CLcav occupied ≥40% of the CL volume (with CLcav diameter 18 mm or less), conception rates improved (62.5% vs. 37.5%), in conjungtion with elevated E2 levels. At CLBP levels of 40% or higher, both CLcav size and P4 concentration reached their peak, but excessive CLBP did not enhance conception rates.

These findings suggest that CLcav does not negatively affect 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 could improve ET efficiency. Future studies should explore the physiological mechanisms that contribure to CLcav formation and its role in reproductive success.