Beneficial Effect of Follicle‐Stimulating Hormone Priming on OPU ‐ IVF in Prepubertal Calves of Japanese Black Cattle (Wagyu)

Hormonal stimulation was performed on Japanese black prepubertal calves (8- and 12-month-old) and heifers (2-3-year-old), followed by oocyte retrieval by ovum pick-up (OPU) and in vitro fertilization (IVF). Both calves and heifers underwent (i) follicle ablation 36 to 48 h prior to follicle-stimulating hormone (FSH) priming, (ii) hormonal stimulation with 100 IU (calves) or 200 IU (heifers) of FSH twice per day (12 h interval) for 2 days, and (iii) OPU following a coasting period of 40 to 42 h after the last FSH injection. Similar number of calves and heifers served as control (without FSH stimulation) at each session, to their FSH primed counterpart. FSH priming significantly increased the numbers of total antral follicles (calves, 23.5-23.7 vs. 8.6-9.9; heifers, 19.5 vs. 5.4, respectively, p < 0.05) and medium and large follicles compared to control animals. Embryo development of oocytes derived from calves post IVF was significantly increased by FSH stimulation, at cleavage (63.1%-66.1% vs. 41.0%-45.1%), blastocyst development (12.7%-13.2% vs. 1.5%-2.1%), and blastocyst yield per OPU per animal (1.4-1.5 vs. 0.1-0.2 embryos, respectively, p < 0.05). Pregnancy rate from transferred blastocysts derived from FSH primed donor calves was significantly improved to 38.6% compared to untreated donors (38.6% vs. 13.3%, respectively; p < 0.05). FSH priming of 8- and 12-month-old Japanese black prepubertal calves prompted a similar blastocyst development (13.2% vs. 12.7%, p > 0.05) of OPU oocytes post IVF. Although FSH priming was equally effective in prepubertal calves and heifers in increasing antral follicle number and recoverable oocytes, on the contrary IVF outcomes, blastocyst yields and pregnancy, were still lower when compared to heifers. In conclusion, OPU-IVF can be applied to FSH-primed prepubertal calves for rapid enhancement of Japanese black cattle characterised by extremely high genetic merits, by significantly reducing generation interval.