Lengthening the superstimulatory treatment protocol increases ovarian response and number of transferable embryos in beef cows

This study determined if lengthening the superstimulation protocol from 4 to 7 days would result in an increase in the superovulatory response with no adverse effects on oocyte/embryo competence in beef cows. Follicular ablation was performed, a progesterone-releasing intravaginal device (PRID) was inserted, and cows were assigned to one of two treatment groups 5 to 8 days after ovulation: Control (4 days of follicle stimulating hormone (FSH)) or Long (7 days of FSH; n = 12 per group). The FSH treatments were initiated 1.5 days later (Day 0). A dose of 400 mg NIH-FSH-P1 (Folltropin-V) was distributed equally over 8 (Control) or 14 (Long) im injections at 12-h intervals. Prostaglandin F2α (PGF) was administered twice, 12 h apart, on Day 2 (Control) or Day 5 (Long), and PRID were removed 12 h after the second PGF. Both groups were given 25 mg pLH (lutropin-V) im 24 h after PRID removal and AI was done 12 and 24 h later. Ova/embryos were collected 7 days after the pLH injection. The mean (± SEM) number of ≥ 9 mm follicles at the time of first AI did not differ (P = 0.24) between groups, but more ovulations (30.9 ± 3.9 vs. 18.3 ± 2.9, P = 0.01) and CL (27.2 ± 2.1 vs. 20.8 ± 2.2, P = 0.04) occurred in the Long group. A higher proportion of the ≥ 9 mm follicles ovulated between 12 and 36 h after pLH in the Long group (93 vs. 69%; P = 0.001). Although numerically higher in the Long group, mean numbers of total ova/embryos, fertilized ova, transferable or freezable embryos did not differ. In conclusion, a lengthened superstimulatory treatment protocol resulted in more follicles acquiring the capacity to ovulate with an increased number of ovulations, and without a decrease in oocyte/embryo competence.