Preovulatory follicular dynamics and ovulatory events following the use of GnRH 84 h after medroxyprogesterone acetate sponge removal in postpartum buffaloes.

Abstract

Herein, we evaluated the effects of Gonadotropin hormone-releasing hormone (GnRH) administration 84 h after medroxyprogesterone acetate (MAP) sponge removal on follicular growth, ovulation timing, and pregnancy per artificial insemination (AI) in cosynchronized postpartum Nili Ravi buffaloes. In this study, 58 Nili Ravi postpartum buffaloes (DIM = 103 ± 1.64) were randomly divided into two treatment groups (n = 29/treatment): GnRH-TAI-84 and TAI-84. All buffaloes were administered a MAP sponge for seven days. Upon MAP sponge removal, all the subjects received prostaglandin F_2α (PGF_2α), and Timed AI (TAI) was performed 84 hours after sponge removal. In the GnRH-TAI-84 group, the buffaloes received GnRH alongside insemination, whereas in the TAI-84 group, the buffaloes were inseminated without GnRH administration. Follicle diameter and blood estradiol levels were measured every 6 h from 72-108 h after MAP sponge removal. The animals were checked for pregnancy using ultrasonography 40 days after AI. Animals subjected to the GnRH-TAI-84 protocol had a higher follicular growth rate and preovulatory follicle size than those in the TAI-84 group. The follicular diameter was also larger in animals that received GnRH-TAI-84 than in those that received TAI-84 90 and 96 h after MAP sponge removal. Buffaloes in the GnRH-TAI-84 group had lower estradiol concentrations at 90, 96, 102, and 108 h than those in the TAI-84 group. Ovulation in GnRH-TAI-84 buffaloes occurred 11 h earlier than that in buffaloes from the TAI-84 group. A shorter interval between AI and ovulation in GnRH-TAI-84 buffaloes (14 h vs. 25 h) led to greater pregnancies per AI (62% vs. 17%) compared to buffaloes from the TAI-84 group.