Origin of the preovulatory follicle after induced luteolysis during the early luteal phase in ewes

Abstract

The origin of the preovulatory follicle (POF) was determined by daily transrectal ultrasonographic examinations in ewes given PGF2α on day 5 (n = 8) or day 9 (n = 8) post-ovulation. In all day-9 ewes, the POF originated from wave 2 while in the day-5 group it originated from wave 1 (n = 5) or wave 2 (n = 3). When the POF originated from wave 2 in day-5 ewes, the dominant follicle of wave 1 emerged earlier than in ewes with the POF from wave 1 (day-1.0 vs. day 0.8, P < 0.05) and was regressing at the time of PGF2α treatment (diameter 4.1 ± 0.4 vs. 2.8 ± 0.3 mm, P < 0.05). The dominant follicle of wave 1 became POF if it was in the growing or plateau phase at the time of luteolysis. If it was already in the regressing phase, the dominant follicle of wave 2 became the POF.