Female to female stimulation of ovarian activity in the ewe

Abstract

The ovulatory and oestrus responses of seasonally anovulatory ewes to the presence of ewes with synchronised oestrus was evaluated. The experiment was carried between 4 June and 1 July when the ewes were in seasonal anoestrus. Two hundred adult Suffolk and Dorset ewes were used. The animals were randomly divided into five groups balanced according to breed: Group I (treated) consisted of 25 ewes induced to cycle by the treatment for 10 days with vaginal sponges containing 40 mg of fluorogestone acetate and an injection of 200 IU of pregnant mares' serum gonadotropin (PMSG) at the time of sponge removal. Group II (mixed) consisted of 25 untreated ewes housed in the same pen as the treated ewes throughout the experiment. Groups III, IV and V each consisted of 50 untreated ewes located in adjacent pens progressively more distant from the pen which contained the treated animals. The ewes in Group III had contact with the treated animals through the fence, while those in Groups IV and V were separated from the treated ewes by one and two pens respectively. Day 0 of the experiment was defined as the day in which the sponges were removed from the treated ewes. Blood samples for progesterone determination were obtained from 25 animals from each group on days 6, 10 and 13. Oestrus was detected twice a day using vasectomised rams introduced to each pen for 15 min in the morning and 15 min in the evening. As expected, the proportion of ewes with luteal activity was higher (P < 0.01) in the treated group than in the other four groups on days 6, 10 and 13. By day 13 progesterone levels were elevated in 87.5%, 52%, 37.5%, 32% and 13% of the ewes sampled in Groups I, II, III, IV and V respectively. There was a direct relationship between the proportion of non-treated ewes with ovarian activity and the intensity of contact with the treated ewes, being maximal in the ewes that remained mixed with the synchronised animals, and lowest in the ewes located in the most distant pen. The proportion of ewes that showed oestrus during the first 14 days after sponge removal was significantly higher in the treated (92%) and mixed (40%) groups than in Groups III (10%), IV (8%) and V (4%). It is concluded that the presence of a large number of ewes in oestrus can stimulate ovarian activity in seasonally anoestrous ewes. This female to female stimulation could be mediated by olfactory, visual and/or auditory stimuli.