Breeding behaviour of a stallion at pasture with 20 mares in synchronized oestrus.

A 6-year-old stallion was placed in a pasture for 9 days with 20 mares in which oestrus was synchronized with two treatments of PGF-2 alpha given 15 days apart. Breeding and observation began 3 days after the second treatment. Observations were carried out during the daylight hours (05:00 to 21:30 h). Eighteen mares showed oestrus and mated an average of 4.56 times each (range 1-12). There were 1.74 mounts per mating. The maximum number of matings by the stallion during 1 day was 16 on Day 2. The overall mean interval between matings was 72.8 min, ranging from 34.5 min on Day 1 to 128.7 on Day 6. The mares were mated at irregular intervals during oestrus but 16 of 18 (88.9%) mares mated at least once during the 3 days preceding the last day of oestrus. Only 5 mares mated on the last day of oestrus. Of the 20 mares, 17 (85%) were pregnant when examined 38 days after the end of the experiment. The results suggest that a stallion will indulge in significantly more mating activity at pasture than is currently expected with hand mating and still achieve a high first oestrus conception rate.