Effect of ovarian stimulation by different gonadotrophin treatments on in vivo and in vitro reproductive efficiency of rabbit does under high ambient temperature.

Abstract

Non-lactating multiparous NZW rabbit does (n = 227) were used in two experiments. In the 1st experiment (n = 87), does were i.m. injected with 0.1-ml saline/doe in day 0 (control, n = 29). Other does were injected with 25IU equine chorionic gonadotrophin (eCG), followed by 0.2-ml gonadotrophin-releasing hormone (GnRH, n = 29) or 75IU human chorionic gonadotrophin (hCG, n = 29) per doe 48h later. After 60h of day 0, does in all groups were artificially inseminated (AI). In the 2nd experiment, does (n = 140) were mated (AI) after synchronization of estrus/ovulation with 25IU eCG, and 75IU hCG 48h later. On day 5 post-AI, does were injected with saline (control), 75IU hCG, 0.2ml GnRH, or 25IU eCG per doe. Injection of eCG with GnRH or hCG pre-AI significantly increased corpora lutea number, ovulation rate, total number/doe and recovery rate of embryos, viable embryos, hatched blastocysts, in vivo reproductive parameters, and concentration of progesterone and progesterone/estradiol 17-β ratio. Injection of eCG on day 5 post-AI significantly improved large and total follicle number, and in vivo reproductive efficiency. The corpora lutea number and impantation sites were significantly increased in the hCG and eCG groups. Fetal loss rate significantly increased only in the GnRH group. Under high ambient temperature, administration of eCG with hCG or GnRH injection pre-AI could be synchronized estrus/ovulation for improving in vivo and in vitro embryo production. In addition, pregnancy outcomes could be enhanced in rabbit does induced to ovulation by a single eCG or hCG dose on day 5 post-AI.