Characterization of the Ovarian Antral Follicle Population and Follicular Dynamics of Ram-Induced Preovulatory Follicles in Ewes According to the Onset of Anoestrus

The ovarian status and its relationship with the ovulatory response to the male effect were studied in Ile-de-France ewes that entered seasonal anoestrus either early (becoming anovulatory on February 7, n = 15) or late (becoming anovulatory on March 7, n = 14). In each group, the male effect was performed 35 days after the onset of anoestrus. Transrectal ultrasonography was performed on days D−7, D−5, D−3 and D0 (ram introduction day) to assess the number and size of ovarian follicles≥2 mm. From D0 to D4, the dynamic of ram-induced preovulatory follicles was monitored, and luteal structures were identified on day D14 or D16. Plasma progesterone levels were measured from D−7 to D14 or 16 to evaluate corpus luteum activity before and during exposure to males. These measurements confirmed the anoestrus status of the ewes at the beginning of the experiment and allowed characterization of short and normal luteal phases. Ultrasound data from ewes 30299 and 10311 in the “early” group, as well as from ewes 10212 and 10308 in the “late” group, were excluded from the dataset due to difficulties in interpreting the ultrasound images. The experiment was conducted at the INRAE Animal Physiology Experimental Facility (PAO, Nouzilly, France; https://doi.org/10.15454/1.5573896321728955E12).