Effect of shortening or lengthening the duration of the cycle on oestrus, ovulation and follicular growth in Lle-de-France sheep

Abstract

Eight-day-long short cycles were induced by prostaglandin five and eight consecutive times in Ilede-France ewes. In both cases, oestrus and ovulations were observed at the end of each short cycle. Normal and atretic follicles larger than 100 μm were counted in the ovaries of five Ile-de-France sheep with five consecutive short cycles (CC 1 group), five Ile-de-France sheep with eight consecutive short cycles (CC 2 group) and five Ile-de-France sheep with cycles blocked with a 40 mg fluorogestone-acetate pessary which was changed after 20 days (CL group). The ovaries of 15 untreated Ile-de-France sheep collected 2 days after oestrus and served as controls. Neither the number of follicles between 100 and 1284 μm, nor the number of follicles larger than 2538 μm, differed between treatments. The number of healthy follicles between 1284 and 2538 μm in diameter, and the number of atretic follicles larger than 1284 μm, made it possible to discriminate between the group of sheep with eight consecutive short cycles and the control group. The number of healthy follicles between 1284 and 2538 μm was found to be twice as great as in the control group (5.9 vs. 3.0). The number of early atretic follicles between 1285 and 3568 μm in the CC 2 group was twice that found in the control group (7.6 vs. 3.1). The number of late atretic follicles of the same size was four times greater in the control group than in the CC 2 group (3.8 vs. 1.0). The category of follicles between 1284 and 2538 μm, associated with early or late atretic follicles larger than 1285 μm, may be considered as a transitory group regulating the renewal of pre-ovulatory follicles from the pool of growing follicles larger than 100 μm.