A note on the effect of continuous ram presence on estrus onset, estrus duration and ovulation time in estrus synchronized ewes

During fall season, 18 multiparous Corriedale ewes were divided into two equal groups for the continuous (CON) and intermittent (INT) presence of a ram. Estrus was synchronized with fluorgestone acetate intravaginal sponges that were left 14 days, plus an injection of 200 mug of a prostaglandin F-2 alpha analog at sponge removal. Estrus was detected three times a day (at 6 a.m., 2 p.m. and 10 p.m.) by using rams with harnessess and markers. Ovulation time was determined by laparoscopy, starting 24 h after estrus detection. Estrus onset was (mean +/- S.E.M.) 32.9 +/- 1.6 and 45.3 +/- 4.4 h for the CON and INT groups, respectively (P < 0.01). Estrus duration was 31.1 +/- 0.9 and 30.2 +/- 1.2 h, for the same groups, respectively (P > 0.05). Ovulation time and the interval from sponge removal to ovulation (ISRO) for the CON and INT groups was 29.0 +/- 1.5, 62.0 +/- 2.0, 26.7 +/- 1.3 and 72.0 +/- 4.2 h, respectively. Ovulation time was not different (P > 0.05), but ISRO was shown to be different between treatments (P < 0.05). It is concluded that the continuous presence of a ram after sponge removal hastens estrus onset and reduces the interval between sponge removal and ovulation, without modifying estrus duration and time between estrus onset and ovulation. (C) 2001 Elsevier Science B.V. All rights reserved.