Ovarian stimulation of Nelore calves and prepubertal heifers with a long-acting recombinant human FSH (corifollitropin-alpha) and subsequent ovum pick-up and in vitro embryo production outcomes

The aim of this study was to evaluate the use of a long-acting recombinant human FSH (rhFSH, corifollitropin-alpha) to induce ovarian stimulation in Nelore breed (Bos indicus) calves and prepubertal heifers prior to ovum pick-up (OPU) for in vitro embryo production (IVEP). In Experiment 1, a dose-response trial was performed to determine the optimal dose of rhFSH, which was determined to be 10 μg. In Experiment 2, 6–7 mo old calves were randomly allocated to receive rhFSH either via sc (n = 5) or im (n = 5). Ovarian follicular development was monitored daily by transrectal ultrasonography for five days. There was no effect of route (P = 0.1348) nor route × time interaction (P = 0.8336) on follicle development. In Experiment 3, 7–8 mo old calves (n = 90) were randomly allocated into 5 groups: 1) Control: no ovarian stimulation; 2) rhFSH-96: 10 μg rhFSH sc followed by OPU 96h later; 3) rhFSH-120: 10 μg rhFSH sc and OPU 120h later; 4) eCG-96: 300 IU eCG im and OPU 96h later; and 5) eCG-120: 300 IU eCG im and OPU 120h later. Non-rhFSH treated Nelore mature cows (n = 10) were used as reference-controls for IVEP outcomes. Treatment with rhFSH increased the proportion of grade I cumulus-oocyte complexes (COC) collected by OPU at either timepoints (96 or 120h) compared with eCG or controls (P < 0.0001). Blastocyst rate for rhFSH-120 calves was similar to mature cows (P > 0.05). Treatment with rhFSH, however, increased the proportion of expanded COC and decreased the proportion of viable COC (P < 0.0001) compared with eCG and controls. In Experiment 4, yearling heifers (n = 60) were treated or not (control group) with 10 μg rhFSH sc and OPU was performed 72 or 96h later. Heifers treated with rhFSH had a greater proportion of grade I COC (P = 0.0188) and blastocyst rate (P < 0.0098) than controls, regardless of the interval used. These groups, however, yielded a lesser number of viable COC (P = 0.0264), resulting in a similar (P = 0.5869) number of embryos produced by donor per OPU compared with controls. Pregnancy rate after embryo transfer was also similar between controls and rhFSH groups (19.3 vs 25.0 %, P = 0.4142). In summary, treatment with a single sc injection of corifollitropin-alpha was effective to promote ovarian stimulation in calves prior to OPU. The potential benefits of stimulatory protocols using rhFSH, however, have been overshadowed by a decrease in the total number of viable COC recovered per donor, thus failing to increase the number of embryos produced per OPU.