Influence of season and age on reproductive activity in pony mares on the basis of a slaughterhouse survey.

Reproductive tracts were collected monthly over a 3-year period from 1,003 nonpregnant ponies at a slaughtering plant in Wisconsin. Ages of the animals were estimated from tooth replacement and wear. Ovaries were examined for follicular and luteal activity. There were no differences between left and right ovaries in size or occurrence of ovulation. The frequency of multiple ovulations, 10%, was higher than previously reported for ponies. The follicular changes during the ovulatory cycle did not support a two-wave theory of follicular growth. Ovarian activity changed seasonally, a finding similar to that reported previously in palpation studies of the pony. The ovulatory season appeared to be shorter, with fewer ponies ovulating throughout the year, than had previously been reported for horses. There were significant differences between animals of different ages in ovarian endpoints and in the proportion of mares that were ovulatory. The percentage of mares ovulatory during the fall was lower in the younger age groups (less than 5 years) than in the older groups, indicating a shorter breeding season for young mares. Ovarian activity appeared to decrease after 15 years. Examination of luteal structures from pre-pubertal and pubertal fillies indicated that the onset of puberty occurred at 12 to 15 months of age.