FEMALE TO FEMALE STIMULATION OF OVARIAN ACTIVITY IN THE EWE

The ovulatory and oestrus responses of seasonally anovulatory ewes to the presence of ewes with synchronised oestrus was evaluated. The expe riment was carried between 4 June and 1 July when the ewes were in sea sonal 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 t he treatment for 10 days with vaginal sponges containing 40 mg of fluo rogestone acetate and an injection of 200 IU of pregnant mares' serum gonadotropin (PMSG) at the time of sponge removal. Group II (mixed) co nsisted of 25 untreated ewes housed in the same pen as the treated ewe s throughout the experiment. Groups III, IV and V each consisted of 50 untreated ewes located in adjacent pens progressively more distant fr om 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 p ens respectively. Day 0 of the experiment was defined as the day in wh ich the sponges were removed from the treated ewes. Blood samples for progesterone determination were obtained from 25 animals from each gro up on days 6, 10 and 13. Oestrus was detected twice a day using vasect omised rams introduced to each pen for 15 min in the morning and 15 mi n in the evening. As expected, the proportion of ewes with luteal acti vity was higher (P<0.01) in the treated group than in the other four g roups on days 6, 10 and 13. By day 13 progesterone levels were elevate d in 87.5%, 52%, 37.5%, 32% and 13% of the ewes sampled in Groups I, I I, III, IV and V respectively. There was a direct relationship between the proportion of non-treated ewes with ovarian activity and the inte nsity 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 oe strus 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 larg e number of ewes in oestrus can stimulate ovarian activity in seasonal ly anoestrous ewes. This female to female stimulation could be mediate d by olfactory, visual and/or auditory stimuli.