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.