383 EFFECT OF TIME OF OVULATION INDUCTION BY GONADOTROPIN-RELEASING HORMONE OR PITUITARY LUTEINIZING HORMONE ON OVA/EMBRYO PRODUCTION IN SUPERSTIMULATED BEEF COWS INSEMINATED AT A FIXED TIME

Abstract

It has been shown than it is possible to AI embryo donors at a fixed time (FTAI) by removing the progestin-releasing device at the time of the last FSH treatment and inducing ovulation with gonadotropin-releasing hormone (GnRH) or porcine luteinizing hormone (pLH) at either 12 h (dairy cows: Bos indicus) or 24 h (beef cows: Bos taurus) after device removal (Bo et al. 2006 Theriogenology 65, 89–101). An experiment was designed to determine the best interval from device removal to GnRH or pLH treatment in Angus (beef cow) donors. Red Angus donors (43 cows and 56 heifers) were blocked by parity and randomly assigned to 1 of 4 treatment groups in a 2 × 2 factorial design. On Day 0, all donors received a DIB vaginal device (Syntex, Buenos Aires, Argentina) plus 2.5 mg estradiol-17β and 50 mg progesterone (P4; Laboratorio Rio de Janeiro, Argentina) IM. Superstimulatory treatments were initiated on Day 4, with a total dose of 320 mg (cows) or 200 mg (heifers) NIH-FSH-P1 of Folltropin-V (Bioniche Animal Health Inc., Belleville, Ontario, Canada) in twice daily IM injections over 4 days. All cows received prostaglandin-F treatment (150 µg d-cloprostenol; Bioprost; Biotay, Buenos Aires, Argentina) on Day 6 (AM and PM); DIB devices were removed with the last Folltropin-V treatment on Day 7 PM. Donors received 0.050 mg GnRH (Lecirelina; Gonasyn; Syntex, Buenos Aires, Argentina) or 25 mg Armour pLH (Lutropin-V; Bioniche) 12 h (Day 8 AM) or 24 h (Day 8 PM) later and were FTAI 12 and 24 h after GnRH or pLH. Ova/embryos were collected nonsurgically and classified according to IETS recommendations on Day 15 AM for donors receiving GnRH or pLH on Day 8 AM and on Day 15 PM for those receiving GnRH or pLH on Day 8 PM. Data were analyzed by two-way ANOVA. Although there was no effect of induction agent (GnRH vs. pLH; P > 0.2) and/or interaction between the induction agent and the time of treatment (P > 0.13) on ova/embryo production, treatment with GnRH or pLH on Day 8 AM (i.e. 12 h after DIB removal) resulted in a significantly lower (P < 0.05) number of fertilized ova and Grades 1 and 2 embryos than treatment on Day 8 PM (i.e. 24 h after DIB removal; Table 1). It was concluded that GnRH and pLH were equally efficacious for inducing ovulation in superstimulated donors that were fixed-time AI. Furthermore, a 24-h interval from progestin device removal to GnRH or pLH administration was preferable for Bos taurus beef donors. Table 1. Ova/embryo production in Angus donors treated with GnRH or pLH 12 or 24 h after removal of a progestin-releasing device and FTAI 12 and 24 h later