# Effects of Synchronized Ovulation Protocols on Reproductive Performance of Beef Cattle in Korea: A Retrospective Study of 755 Cases

## TL;DR

This study compares three hormone protocols for synchronized ovulation in Korean beef cattle and finds that the CIDR protocol leads to the highest pregnancy rates, especially in young cows.

## Contribution

The study provides farm-specific evidence on the effectiveness of synchronized ovulation protocols in Korean Hanwoo cattle.

## Key findings

- The CIDR protocol achieved the highest pregnancy rate (58.3%) compared to GPG (47.5%) and GPPG.
- CIDR was most effective in young cows and first-time inseminations, with success rates up to 70%.
- CIDR consistently induced optimal follicle sizes (13–16 mm) and improved luteinizing hormone levels.

## Abstract

Cattle farms require efficient breeding methods to increase pregnancy rates, but selection of the most suitable hormone treatment protocol for each farm can be challenging. This study compared three hormone-based synchronized ovulation protocols commonly used in Korean cattle farms to identify which protocol is most effective for particular groups of cows. Pregnancy rates, follicle development, and blood hormone levels were evaluated in 540 cows using three protocols: CIDR, GPG, and GPPG. The CIDR protocol achieved the highest pregnancy rate (58.3%), whereas the GPG protocol showed the lowest (47.5%). The CIDR protocol was particularly effective in younger cows and at the first artificial insemination, reaching up to 70% success in some groups. Medium-sized follicles (13–16 mm) produced the highest pregnancy rates, and the CIDR protocol most consistently induced follicles of this optimal size. Blood tests indicated that the CIDR protocol established a more favorable hormonal environment for successful breeding. These findings provide cattle farmers with practical evidence to guide the selection of effective breeding strategies, ultimately improving farm productivity and reducing breeding costs.

Reproductive outcomes following synchronized ovulation protocol in beef cattle are influenced by multiple factors, making protocol selection based on farm-specific conditions essential. This retrospective study analyzed the relationship between pregnancy rates and associated factors under the CIDR (GnRH with CIDR insertion–PGF2α with CIDR removal–GnRH), GPG (GnRH–PGF2α–GnRH), and GPPG (GnRH–PGF2α–PGF2α–GnRH) protocols in Hanwoo cattle. The highest pregnancy rate was observed with the CIDR protocol (58.3%), whereas the GPG protocol yielded the lowest (47.5%). The CIDR protocol demonstrated superior suitability compared with the GPG protocol in first service (61.0% vs. 47.0%) and young breeding cattle (parity: 0–2; 61.6–70.0% vs. 47.5–48.6%). The dominant follicle size strongly associated with pregnancy success was 13–16 mm, and the CIDR protocol induced these follicles more frequently than the GPG protocol (50.2% vs. 35.5%). Although interpretive bias may exist from data collected from pregnant animals only, CIDR protocol significantly increased luteinizing hormone levels compared to GPG. The GPPG protocol produced outcomes that were improved relative to the GPG protocol and statistically comparable to the CIDR protocol. These findings addressed the study’s objective, identifying optimal synchronized ovulation strategies and underscoring reproductive management importance for Korean Hanwoo operations.