Ovulation and follicular growth in gonadotropin-treated gilts followed by in vitro fertilization and development of their oocytes.

We investigated whether porcine ovaries derived from FSH-pituitary (FSH-P) or hCG-treated animals can produce oocytes with better in vitro cytoplasmic maturation and in vitro embryonic development relative to those derived from saline-treated animals. The size of the follicle producing the oocyte was also studied. Each of 25 prepubertal gilts received 1 of 6 treatments by intramuscular injection: 1) saline (3 mL, once, n = 5); 2) FSH-P8-3 (8 mg, 3 times, with a 24-h interval, n = 4); 3) FSH-P16-3 (16 mg, 3 times, with a 24-h interval, n = 4); 4) FSH-P16-1-P4-2 (16 mg, once, 4 mg, twice, with a 24-h interval, n = 4); 5) FSH-P16-1 (16 mg, once, n = 4); or 6) hCG (100 IU, 3 times, with a 24-h interval, n = 4). The ovaries were removed by mid-ventral laparotomy 72 h after the first injection. The numbers of corpora hemorrhagica (CH) with each FSH-P treatment were similar (P > 0.05). However, compared with gilts treated with saline or hCG, those treated with FSH-P8-3 had a greater (P < 0.05) number of CH. Treatment with FSH-P8-3 or FSH-P16-3 induced significant growth of medium/large follicles (4 to 8 mm in diameter) compared with saline or FSH-P16-1. The same results were observed when FSH-P8-3 was compared with FSH-P16-P4-2 or hCG. After in vitro fertilization, the rates of male and female pronuclei in oocytes derived from medium/large follicles did not differ (P > 0.05) between treatments, but in oocytes derived from small follicles they were lower (P < 0.05) in saline-treated than in FSH-P16-1-P4-2-treated gilts. After 120 h in culture, the percentages of the inseminated oocytes from 1 to 3 mm or 4 to 8 mm follicles developing to > or = 2-cell did not differ (P > 0.05) between saline- and gonadotropin-treated gilts. However, a higher (P < 0.05) percentage of the inseminated oocytes from 4 to 8 mm follicles had developed to the morula stage or beyond, than those from the 1 to 3 mm follicles. In conclusion, administration of single or multiple doses of FSH-P induced ovulation, but only 8 or 16 mg FSH-P injected 3 times with 24-h intervals for 72 h induced growth of 4 to 8 mm follicles. The size of follicle from which the oocyte derived also had a significant effect on its development in vitro.