Continuous presence of rams hastens the onset of estrus in ewes synchronized during the breeding season

The objective of the study was to investigate whether ram exposure would af fect the onset of estrus in synchronized ewes, during the breeding season. Ninety pluriparous ewes (30 White Face, 30 Suffolk and 30 Hampshire) were d ivided by breed and estrous synchronized with intravaginal sponges. These s ponges were impregnated with medroxyprogesterone acetate and inserted for 1 2 days at unknown stages of the estrous cycle. Half of the females in each breed were exposed to a ram immediately following sponge removal and throug hout an 120-h period (group IMM) while the other half was subjected to ram exposure at 48 h after sponge removal (group LAT). The same ram was used fo r both groups. In the LAT group the male was housed in a pen adjacent to th e female pen, Estrus onset for group IMM occurred (mean +/- S.D.) 32.9 +/- 12.3 h after sponge removal while in group LAT estrus occurred at 53.1 +/- 19.6 h, respectively (P < 0.0001), The number of females in estrus at 48 h was 43/45 (95.6%) for the IMM group and 26/41 (63.4%) for the LAT group (P < 0.001). At 60 h 43/45 (95.6%) and 31/41 (75.6%) of the ewes of the IMM an d LAT groups showed estrus, respectively (P < 0.01). At 120 h after sponge removal, all the females from IMM group showed estrus (45/45) while 41/44 ( 93.2%) from the LAT group did (P > 0.05). These results show that immediate exposure to a ram at sponge removal hastens estrus onset in ewes estrous s ynchronized during the breeding season. (C) 2000 Elsevier Science B.V. All rights reserved.