297 EFFECT OF GONADOTROPIN-RELEASING HORMONE COMPARED WITH ESTRADIOL-17β AT THE BEGINNING OF A SUPERSTIMULATION PROTOCOL ON SUPEROVULATORY RESPONSE AND EMBRYO QUALITY

Abstract

Success of a superstimulation protocol is largely dependent on avoiding the effects of the dominant follicle. The objective of this study was to determine if gonadotropin-releasing hormone (GnRH) would serve as a suitable alternative to the traditional estradiol-17β in a superstimulation protocol when using a CIDR. Dairy cattle (n = 411) were superstimulated using one of two treatment protocols. The GnRH-treated animals received a CIDR on random days of the estrous cycle (day 0), and GnRH was injected i.m. (100 micrograms of Cystorelin) on day 3. Porcine FSH (Folltropin-V) was administered twice daily in decreasing doses on days 5 to 8, and on day 8, CIDR were removed and 25 mg of dinoprost (PGF_2α) was administered twice. The Estradiol-treated animals received a CIDR and 4 mg estradiol-17β i.m. on random days of the estrous cycle (day 0). Porcine FSH was administered twice daily in decreasing doses on days 4 to 7, and on day 7, CIDR were removed and 25 mg of PGF_2α was administered twice. All animals were artificially inseminated at standing estrus and at 6-h intervals during estrus. Animals were inseminated a minimum of twice, and those with extended estrous periods were inseminated three times. Animals not showing estrus were inseminated once 48 h after CIDR removal. Seven days following estrus, embryos were collected. For data analysis, animals were divided into lactating cows, dry cows, and heifers. Dosage of FSH for each animal varied according to previous response rates; therefore, animals were further subclassified as high FSH (≥300 mg in 15 mL) or low FSH (<300 mg in 15 mL). As there were no heifers on high FSH, data analysis was done as a 5 × 2 factorial ANOVA. Total number of ova/embryos, quality, development, and fertilization rates were recorded. Analysis of data showed no statistical differences (P > 0.05) between Estradiol- and GnRH-treated groups for number ova/embryos recovered (9.8 ± 0.58 v. 9.7 ± 0.65), IETS-grade 1 and 2 embryos (4.7 ± 0.37 v. 4.5 ± 0.41), percentage fertilized (54.1 ± 2.5 v. 53.2 ± 2.9), and percentage grade 1 and 2 embryos (49.2 ± 2.5 v. 49.3 ± 2.8), respectively. No significant interactions were found between treatment and lactation status or treatment and FSH dose. Data suggest that GnRH in combination with a CiDR is an effective means of synchronizing follicle wave emergence in a superstimulation protocol.

George Seidel, Josh Walker, John Hassler, and Sam Galphin.