GnRH supplementation in the PreOvsynch protocol targeting follicular cysts enhances synchronization and reduces days...

Achieving timely pregnancy postpartum is essential for dairy herd fertility, yet reproductive efficiency is often constrained by ovarian dysfunction, particularly follicular cysts. This study monitored ovarian and uterine status via ultrasonography at 21, 35, and 42 days in milk (DIM) in 484 dairy cows managed under a PreOvsynch protocol, identified key disorders limiting fertility, and evaluated a targeted optimization strategy. Results showed that follicular cysts were the most prevalent postpartum disorder, peaking at 42 DIM in primiparous cows (22.1%) and at 35 DIM in multiparous cows (>25%). Blood biochemical analysis revealed weakened antioxidant capacity in cyst-affected cows and highlighted pathological distinctions between follicular and luteal cysts. Based on these findings, an optimized PreOvsynch protocol was developed by administering a supplemental GnRH injection 7 days before protocol initiation (35 DIM). The optimized protocol effectively treated follicular cysts (57.69% cure rate) and significantly improved reproductive outcomes compared with the standard protocol, including the proportion of cows with a corpus luteum before the first PGF₂α injection (66.13% vs. 51.43%), ovulation rate after the first PGF₂_α injection ₍77.27% vs. 61.97%), and ovulation rate after the second PGF₂_α (84.78% vs_. 74.36%). Consequently, it shortened the herd's days open (86.77 vs. 95.46 days). In conclusion, our findings demonstrate that supplementing the PreOvsynch protocol with a single pre-initiatory GnRH injection effectively mitigated the negative impact of follicular cysts, thereby improving PreOvsynch outcomes and enhancing overall reproductive efficiency in dairy cows.