OVARIAN AND ESTROUS ACTIVITY THROUGHOUT THE YEAR IN PREGNANT AND NONPREGNANT EWES SELECTED FOR EXTENDED BREEDING SEASON
Twenty-nine DLS (1/2 Dorset, 1/4 Leicester, 1/4 Suffolk) ewes selected for extended breeding season, were involved in this study which lasted for 18 mo. According to their lambing date relative to January first, 15 ewes had a high lambing index whereas the others had a low index, the difference being 33 days (P < 0.01). Half the ewes were assigned at random to remain nonpregnant throughout the study, whereas the other half was mated in July and August. From 1 May to 15 July, 20 ewes (69%) were cycling of which 81% were from the high and 54% from the low index group (0.05 > P < 0.10). Two ewes (7%) continued cycling throughout the summer, whereas the remaining 18 ewes experienced a period of summer anestrus which occurred on 27 May (± 3.5 days) and lasted for an average of 63 ± 2.6 days. The first ovulation (unaccompanied by estrus) was observed on 29 July (± 2.6 days) the second ovulation, 20 days later was accompanied by estrus. The breeding season in nonpregnant ewes lasted 194 ± 3.2 days ending on 1 Mar. (± 7.3 days). The average lambing date of the 15 pregnant ewes was 8 Jan. (± 2.8 days). Seven of these ewes exhibited at least one ovulation postpartum, but in only two ewes was the ovulation accompanied by estrus. Introducing rams daily indicated that marker rams were successful in detecting only 88% of the ewes in estrus. Sixty-six percent of the false heats were observed prior to resumption of the regular estrous cycle. Key words: Ovarian activity, estrous activity, pregnancy, extended breeding season, estrus detection