HAREM SIZE AND REPRODUCTIVE SUCCESS OF STALLIONS IN MISAKI FERAL HORSES

Over a 16-year period (1979-1994), long-term investigations were carri ed out on 14 Misaki feral stallions to analyze changes in harem size a nd the reproductive success. Harem size changed with the age of the st allions. Most stallions formed harem groups with four to five mares at the age of 4-6 and then the number of mares increased rapidly to the maximum at the age of 6-9 years, Thereafter, harem size decreased grad ually to a minimum with advancing age. The harem size of 60 stable har em groups ranged from 1 to 9, and the average varied from a minimum me an of 1.8 in 1988 to a maximum mean of 5.3 in 1982. Mean harem size in creased as adult sex ratio increased and a significant and positive co rrelation was found between them. One hundred and ninety-eight sire-fo al pairs were determined by a paternity test with blood types and cons ort relations between stallions and mares during the study period. Out of 99 foals which were born in the stable harem groups, the true sire s of 84 foals (85%) were the harem stallions in which the foals were b orn but the remaining 15 foals (15%) were sired by other harem stallio ns. Two out of three stallions which were studied throughout their lif etime produced 24 and 25 foals in 10 and 11 years of their reproductiv e lifespan, respectively. Another one produced only five foals in 6 ye ars. The number of foals sired by the harem stallions was less than tw o over harem size 7 and some of the foals born in the harem were sired by other harem stallions. These results suggest that if a particular stallion monopolizes too many mares, he could not sire so many offspri ng because he could not always prevent his rival stallions from mating with his mares in wild or feral circumstances.