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

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.