Close synchrony of ovulation in superstimulated heifers that have a downregulated anterior pituitary gland and are induced to ovulate with exogenous LH.

ABSTRACT

The synchrony of ovulation was examined in superstimulated heifers that had a downregulated pituitary gland and which were induced to ovulate by injection of exogenous LH. The pituitary was downregulated and desensitized to GnRH by treatment with the GnRH agonist deslorelin. Nulliparous heifers (3.5 yr old) at random stages of the estrous cycle were assigned to 1 of 3 groups, and on Day -7 received the following treatments Group 1 (control, n = 8), 1 norgestomet ear implant; Group 2 (GnRH agonist, n = 8); Group 3 (GnRH agonist-LH protocol, n = 8), 2 deslorelin ear implants. Ovarian follicle growth in all heifers was superstimulated with twice-daily intramuscular injections of FSH (Folltropin-V) 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 PGF (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, i.m. porcine LH (Lutropin) 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 ovulate. 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 injected 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 agonist-LH superovulation protocol, with significant practical and economic advantages for superovulation and embryo transfer programs.