Effects of delaying the LH surge and altering LH secretion on plasma hormones and embryo production in heifers superstimulated with FSH

Ovarian follicles were ablated by ultrasound-guided transvaginal aspiration in 20 Holstein heifers allocated to four groups (n = 5 per group). The first group (SOV) was superstimulated conventionally with FSH. In the other superstimulated groups, the LH surge was delayed by 24 h with progesterone (CIDR) and 100-μg injection of GnRH. The second group (CIDR-3.5d) received the CIDR on the second day of superstimulation. To increase LH pulsatility, the third group (CIDR-3.5d-GnRH-Pulsed) received repeated 5-μg injections of GnRH during superstimulation and the fourth group (CIDR-7d), received the CIDR with a first prostaglandin, 2 d prior to superstimulation. The number of corpora lutea (CL) and embryos was not significantly different (P > 0.1) in CIDR-3.5d compared to SOV (9.4 ± 2.0 vs. 13.8 ± 2.0 CL and 3.6 ± 1.2 vs. 5.8 ± 1.2 embryos, respectively). In the CIDR-3.5d-GnRH-Pulsed group, the 100-μg injection of GnRH failed to induce an LH surge and there were no CLs and no embryos recovered. In the CIDR-7d gr...