REPRODUCTIVE RESPONSE IN HAIR SHEEP SYNCHRONIZED WITH MEDROXYPROGESTERONE ACETATE IMPREGNATED IN NON-COMMERCIAL INTRAVAGINAL SPONGES

Abstract

Background. Intravaginal sponges impregnated with medroxyprogesterone acetate or fluorogestone acetate are routinely used in oestrus synchronization protocols in sheep, non-commercial sponges are a viable option in the reproductive control of female sheep. Objective. To evaluate the reproductive response in hair sheep synchronized with medroxyprogesterone acetate impregnated in non-commercial intravaginal sponges. Methodology.  31 adult hair sheep 5/8 Pelibuey x 2/8 Black Belly x 1/8 Dorper, average weight of 40 ± 3.2 kg and a body condition of 3-3.5 were used. They were randomly assigned to one of four treatments: T1 (n = 8 ewes), 5 mg of medroxyprogesterone acetate impregnated in non-commercial intravaginal sponges + 1 mg of estradiol cypionate + 200 IU of eCG; T2 (n = 8 ewes), synchronization similar to T1, but 500 IU of eCG were applied; T3 (n = 8 ewes), 20 mg of fluorogestone acetate impregnated in intravaginal sponges + 200 IU of eCG; T4 (n = 7 ewes), synchronization similar to T3, but 500 IU of eCG were applied. In all treatments the sponges were placed for 10 days. Blood samples were collected by jugular puncture and the concentrations of progesterone and LH were determined. Results. The sponge removal interval to estrus was different (P <0.05) between T1 and T3 (14.5 ± 5.5 and 38.8 ± 2.5 h, respectively). Estrus duration was similar (P> 0.05) between T1, T2 and T3 (54.5 ± 5.5, 46.5 ± 5.8 and 38.3 ± 2.6 h, respectively), T4 (59.3 ± 4.1 h) was similar (P> 0.05) to T1 and T2 (54.5 ± 5.5 h and 46.5 ± 5.8 h, respectively) but different (P <0.05) from T3 (38.3 ± 2.6 h). The progesterone concentration was higher than 1 ng ml-1, on days 0 to 4 (T2), 0 to 5 (T4) and 0 to 7 (T1 and T3), then it decreased to <1 ng ml-1 in all the treatments. The sponge removal and oestrus onset intervals at the LH preovulatory peak were similar (P> 0.05) between treatments, however, the LH profile at T1 and T2 shows scattered elevations. 5 mg of medroxyprogesterone acetate + 1 mg of estradiol cypionate, impregnated in non-commercial sponges advance oestrus and do not adjust for the occurrence of LH preovulatory peak. Implications. The study demonstrates that it is feasible to use reduced doses of medroxyprogesterone acetate impregnated in non-commercial intravaginal sponges in estrous synchronization protocols in hair sheep, the progesterone profile confirms the inhibitory effect of the drug on GnRH / LH secretion. Conclusion. The application of 200 or 500 IU of eCG does not modify the occurrence or duration of estrus and the LH preovulatory peak. It is suggested that it is feasible to synchronize hair sheep under tropical conditions with reduced doses of medroxyprogesterone acetate impregnated in non-commercial sponges, however, dispersion of ovulation may occur, which would reduce fertility. The use of eCG and estradiol cypionate does not affect the effectiveness of synchronization.