351 A COMPARISON OF 2 APPROACHES FOR THE USE OF GnRH TO SYNCHRONIZE FOLLICLE WAVE EMERGENCE FOR SUPEROVULATION

Abstract

Although oestradiol has been used successfully to synchronize follicle wave emergence for superovulation, it cannot be used in many countries. Attention has turned to alternatives, including the use of GnRH to induce ovulation of a dominant follicle, which will be followed by emergence of a new follicular wave in 1 to 2 days. However, GnRH synchronizes follicular wave emergence only when it induces ovulation and administration of GnRH at random stages of the oestrous cycle results in ovulation in less than 60% of animals. The objective of the study was to compare superovulatory response and ova/embryo production following synchronization of follicle wave emergence for superovulation with GnRH administered 2 days after insertion of a progestin device, with a protocol in which GnRH is administered 7 days after administration of prostaglandin F_2α and a progestin device. Beef donors of various breeds were placed at random into 1 of 2 groups and superstimulated by replicate so that one cow in each group had ova/embryos collected on the same day. Sixty-six superstimulations were performed in this study; 26 were performed in 13 donors that were superstimulated twice in a crossover design, and 40 donors were superstimulated once (i.e. 20 donors in each treatment group). Cows in group 1 received CIDR devices (Zoetis Animal Health, USA) on Day –2 and 100 μg of GnRH (Cystorelin, Merial USA) on Day 0; FSH treatments were initiated on Day 2 with 288 mg of Folltropin-V (Vetoquinol, Canada) given in twice-daily decreasing doses for 4 days. Prostaglandin F_2α (PGF; 35 mg dinoprost, Lutalyse, Zoetis) was given with the last 2 injections of Folltropin-V and CIDR were removed with the last Folltropin-V administration (i.e. Day 6). Donors received a second GnRH at the onset of oestrus and were AI 8 and 20 h later. Donors that were still in standing oestrus at the second AI were AI again at 30 h. Ova/embryo collections were done on Day 14 and embryos were classified according to the IETS manual. Cows in group 2 received an injection of PGF and a CIDR on Day –7 and 100 μg of GnRH on Day 0; FSH treatments were initiated on Day 2 and the remainder of the treatment protocol was as in group 1. Data (total ova/embryos collected and transferable embryos) were analysed by ANOVA for mixed models, using treatment as a fixed variable and cow (i.d.) as a random variable. The group 1 cows produced a mean (± s.e.m.) of 18.6 ± 1.9 total ova/embryos of which 12.7 ± 1.5 were of transferable quality (7.2 ± 1.3 grade 1). Cows in group 2 produced a mean (± s.e.m.) of 19.5 ± 1.7 total ova/embryos, of which 14.8 ± 1.5 were of transferable quality (8.9 ± 1.2 grade 1). Although 2 more transferable embryos were obtained in group 2, differences were not significant (P > 0.3). At the same time as this experiment was done, 214 other cows were superstimulated in this practice, yielding an average of 7.9 transferable embryos per donor. Results suggest that both approaches are efficacious for the superstimulation of beef cows.

Special thanks to Vetoquinol/Bioniche Animal Health, USA for support.