REGULATION OF ESTRADIOL AND OXYTOCIN INDUCED LUTEOLYSIS IN GAROLE EWES*

摘要

This experiment was conducted to study the effect of estradiol and oxytocin administration during different phase of diestrus in Garole ewes with or without progesterone pre-exposure. Thirty five regular cycling estrous synchronized ewes of 15-20 kg and 2 to 3 years of age were divided into 7 groups of five ewes each, On day 1 (day 0 = day of estrous) 40 mg progesterone was administered to groups 1, 2 and 3 whereas groups 4, 5 and 6 were kept untreated. Estradiol valerate (500 ug) was administered ondays 5 & 6 to groups 1 and 4, on days 7 & 8 to groups 2 and 5, on days 9 & 10 to groups 3 and 6. Group 7 served as control and received no treatments. The ewes were observed for heat twice daily by a vasectomized ram after the estradiol treatment and blood progesterone was measured on the third day of estradiol treatment. Groups 1 and 2, pre-exposed to progesterone responded to estradiol treatment on days 5 & 6 and days 7 & 8 by returning to heat on days 8 ± 0.32 and 9.8 ± 0.38 respectively with progesterone concentration of 0.47 ± 0.07 ng/ ml and 0.58 ± 0.05 ng/ml respectively, Groups 4 and 5 had no progesterone pre-exposure and showed normal estrous cycle that did not differ significantly (P>0.05) from control. However, estradiol treatment on day 9 & 10 brought ewes of group 3 and 6 to heat on day 12.2 ± 0.2 and 11.4 ± 0.25 respectively that did not differ significantly (P>0.05). The results indicate that progesterone pre-exposure is required by the endometrium for release of luteolytic doseof PGF_(2a) though estradiol and oxytocin has stimulatory effect on endometrium for the release of PGF, .