116 EFFECT OF EXOGENOUS PROGESTERONE AND GONADOTROPIN-RELEASING HORMONE APPLICATION ON MAINTENANCE OF PREGNANCY IN EARLY PREGNANT EWES AFTER PROSTAGLANDIN F2 ALPHA INJECTION

Abstract

In this experimental study, we tested the hypothesis that exogenous progesterone and GnRH applications would prevent the detrimental effect of prostaglandin F_2α (PGF_2α; a) on early pregnancy in ewes by sustaining high plasma progesterone level. For this purpose, 9 pregnant ewes (mating day = 0) were divided into 2 groups on Day 18 as follows: (1) PGF_2α group (125 μg of d-cloprostenol injection on Day 18, n = 5); (2) PGF_2α + progesterone sponge group (125 μg of d-cloprostenol injection on Day 18 + 20 mg flugestone acetate for 7 days, n = 4). Moreover, gonadotropin-releasing hormone (GnRH; 10 μg of buserelin acetate, n = 4) was injected intramuscularly to PGF_2α + progesterone sponge group ewes on Day 22 after mating to induce luteinization in dominant follicles. The progesterone sponge was withdrawn on Day 25. Plasma progesterone (P4) concentration was measured on Days 18 and 19 by ELISA. Pregnancies were examined by using transrectal ultrasonography on Days 18, 22, 25, and 35 after mating. Statistical difference between groups was analysed by Chi-squared test. P4 concentration declined to below 1 ng mL^–1 on Day 19 in both groups. While all pregnancies were terminated (5/5) in the PGF_2α group by Day 25, progesterone sponge application prevented pregnancy loss (4/4) in the PGF_2α + progesterone sponge group (P < 0.02). When the progesterone sponge was withdrawn on Day 25, half of the pregnancies (2/4) continued after GnRH application in the PGF_2α + progesterone sponge group until birth. In conclusion, results suggest that exogenous progesterone application is sufficient for maintaining early pregnancy in ewes, even if the corpus luteum is regressed. Furthermore, GnRH application on Day 22 after mating might luteinize dominant follicles and could be sufficient to maintain pregnancy after exogenous progesterone is removed.