Non-ovulatory follicles: characteristics, causes, and solutions?

Abstract

Ovulatory failure during the breeding season is a frustrating development. Non-ovulatory follicles have been called hemorrhagic anovulatory follicles (HAF), anovulatory hemorrhagic follicles, hemorrhagic follicles or persistent anovulatory follicles. Although most workers agree that anovulatory follicles are more common early or late in the season, they do sometimes occur during the normal breeding season, especially in older mares.1 One investigator examined 737 cycles in 47 mares that were treated repeatedly with cloprostenol (CLO) and human chorionic gonadotropin (hCG) over a three year period.2 . The failure of ovulation was more common in the autumn (September/October 22%, November 59%), and approximately 50% of the mares developed an anovulatory follicle during at least one cycle, and 26% experienced them during at least two cycles. A tendency for an anovulatory follicle to recur in a mare from one breeding season to the next was noted. Others have reported no effect of season3 or the highest incidence from May to August,4 but again found a tendency for some mares to have repeated ovulation failure.