CLOSE SYNCHRONY OF OVULATION IN SUPERSTIMULATED HEIFERS THAT HAVE A DOWN-REGULATED ANTERIOR-PITUITARY GLAND AND ARE INDUCED TO OVULATE WITHEXOGENOUS LH

The synchrony of ovulation was examined in superstimulated heifers tha t had a downregulated pituitary gland and which were induced to ovulat e by injection of exogenous LH. The pituitary was downregulated and de sensitized to GnRH by treatment with the GnRH agonist deslorelin. Null iparous heifers (3.5 yr old) at random stages of the estrous cycle wer e assigned to 1 of 3 groups, and on Day -7 received the following trea tments: Group 1 (control, n = 8), 1 norgestomet ear implant; Group 2 ( GnRH agonist, n = 8); Group 3 (GnRH agonist-LH protocol, n = 8), 2 des lorelin ear implants. Ovarian follicle growth in all heifers was super stimulated with twice-daily intramuscular injections of FSH (Folltropi n-V (R)): Day O, 40 mg (80 mg total dose); Day 1, 30 mg; Day 2; 20 mg; Day 3, 10 mg. On Day 2, all heifers were given a luteolytic dose of P GF (7 A.M.), Norgestomet implants were removed from heifers in Group 1 (6 P.M.). Heifers in Group 3 were given an injection of 25 mg, im por cine LH (Lutropin (R)) on Day 4 (4 P.M.). Ovarian follicle status was monitored at 8-h intervals from Day 3 (8 A.M.) to Day 6 (4 P.M.) using an Aloka Echo Camera and 7.5 MHz transducer. Heifers in Groups 2 and 3 exhibited estrus earlier (P < 0.05) than heifers in Group 1. Heifers in Group 2 did not have a preovulatory LH surge and they did not ovul ate. Individual control heifers in Group 1 ovulated between 12 A.M. on Day 5 and 8 A.M. on Day 6. Heifers with deslorelin implants and injec ted with LH in Group 3 ovulated between 4 P.M. on Day 5 and 8 A.M. on Day 6. It was confirmed that superstimulated heifers with GnRH agonist implants can be induced to ovulate with LH. It was also demonstrated that ovulation is closely synchronized after injection of LH. Thus, a single, fixed-time insemination schedule could be used in a GnRH agoni st-LH superovulation protocol, with significant practical and economic advantages for superovulation and embryo transfer programs. (C) 1998 by Elsevier Science Inc.