Effects of follicle stimulating hormone (FSH) on follicular development, oocyte retrieval, and in vitro fertilization (IVF) in ewes during breeding season and seasonal anestrus

Administration of FSH increases the number of developing follicles, and affects oocyte health and cleavage rate. To determine the optimal level of FSH treatment, studies were conducted during the normal breeding season and seasonal anestrus. In Experiment 1, ewes were implanted with Syncro-Mate-B (SMB; norgestomet) for 14 days during the breeding season. Beginning on day 12 or 13 after SMB implantation, ewes were treated with saline (control; n=10), or treated with FSH for two days (2D; n=9) or three days (3D; n=10). In Experiment 2, conducted during seasonal anestrus, ewes were implanted with SMB for 14 days (n=23) or were not implanted (n=26). The SMB-implanted and nonimplanted ewes were assigned to one of three treatments as in Experiment 1: control (n=13), 2D (n=21) or 3D (n=15). In Experiments 1 and 2, ewes were laparotomized to count the number of follicles less than or equal to 3 mm and > 3 mm and to retrieve oocytes. Healthy oocytes from each treatment were used for IVF. In Experiment 3, ewes (n=6) were implanted twice with SMB for 14 days during seasonal anestrus. Ewes were injected with FSH for 2 days, and the oocytes were collected and fertilized as in Experiments 1 and 2. In Experiment 1, FSH-treatment increased (P < 0.05) the number of follicles > 3 mm, the number of oocytes retrieved from follicles less than or equal to 3 mm and > 3 mm, the proportion of healthy oocytes, and the number of oocytes used for IVF. Oocytes from control and 2D ewes had greater (P < 0.01) cleavage rates than 3D ewes (68% and 71% vs. 42%). In Experiment 2, implanted and nonimplanted ewes had similar (P > 0.05) numbers of follicles, total oocytes, and healthy oocytes; therefore, data were combined. The FSH treatment increased (P < 0.01) the number of follicles > 3 mm, and the number of oocytes recovered from follicles > 3 mm. The recovery rate of oocytes and the percentage of healthy oocytes were similar for control and FSH-treated ewes. The cleavage rate in Experiment 2 ranged from 4 to 16%. In Experiment 3, the cleavage rate for ewes treated twice with SMB was 27% which tended to be greater (P < 0.07) than for the 2D ewes that received one SMB implant in Experiment 2. These data indicate that FSH increased the number of developing follicles and the number of healthy oocytes retrieved from ewes during the breeding season and seasonal anestrus. However, cleavage rates during seasonal anestrus were lower than during the normal breeding season in both FSH-treated and control ewes. Treatment of ewes for 2 days with FSH resulted in a greater cleavage rate than treatment of ewes for 3 days.