Follicular and gonadotrophic changes during transition from ovulatory to anovulatory seasons
Snyder, D.A.; Turner, D.D.; Miller, K.F.; Garcia, M.C.; Ginther, O.J.
Journal of Reproduction and Fertility. Supplement 1979(27): 95-101
1979
ISSN/ISBN: 0449-3087 PMID: 289845 Document Number: 142559
Changes in plasma gonadotropin levels and in the follicles were monitored in 14 pony mares for 31-day periods beginning at the penultimate and at the last ovulation of the season. There were no main effects or interactions of day or period on the numbers of small follicles (<20 mm in diameter). Concentrations of FSH, numbers of large follicles (>20 mm), and oestrous behaviour each showed an effect of day (P<0.01), but no effect of period. After the penultimate ovulation, the diameter of the largest follicle was correlated with the number of large follicles (0.65, P<0.001) and the LH concentration (0.44, P<0.001), and after the last ovulation, the diameter of the largest follicle was correlated with the number of large follicles (0.80, P<0.001) and the number of small follicles (0.30, P<0.01). It was concluded that, of the factors considered, the failure to ovulate at the onset of the anovulatory season was due to lack of an adequate ovulatory LH surge and incomplete final maturation of a preovulatory follicle.