PSIII-5 - Evaluation of Gnrh Administration Day in the 7 & 7 Synch Protocol for Fixed-timed Artificial Insemination in Multiparous Beef Cows

Abstract: The objective was to determine the effects of a decreased interval of progesterone on the ovulatory follicle prior to fixed-timed artificial insemination (FTAI) in a 7 & 7 Synch estrous synchronization protocol using estrus expression (EE), FTAI pregnancy rates (AIPR) on 37±2d, and overall pregnancy rates (OPR) after a 60d bull exposure 90±2d determined via ultrasound. Using conventional Angus semen, multiparous Angus-cross cows (n=201) from two locations were randomized by age and days post-partum into two treatments. Both treatments used a controlled internal drug releasing device (Eazi-breed^TM CIDR; 1.38g progesterone) inserted intravaginally –14d of the protocol simultaneous to administration of prostaglandin F2α (PGF; 500µg cloprostenol sodium; Estrumate^®). In the first treatment (7&7), gonadotropin-releasing hormone (GnRH; 86µg gonadorelin; Fertagyl^®) was administered on –7d. In the second treatment (8&6), GnRH was administered on –6d. Both treatments were then administered PGF simultaneous to CIDR removal on 0d, 66±2h prior to FTAI and administration of GnRH. EE was determined at the time of artificial insemination using an Estrotect^TM patch (Rockway Inc., Spring Valley, WI). EE was signified as a patch with 50% or more of the color rubbed off or missing. Subsequently, a patch with less than 50% of the color rubbed off, was not. AIPR, OPR and EE were analyzed by treatment using the GLIMMIX procedure on SAS 9.4 (SAS Institute Inc., Cary, NC.). There was a significant effect on EE (P=0.01), a tendency on PR (P=0.08), and no effect on OPR (P=0.53) by treatment. EE, AIPR, and OPR for 7&7 were 95±2.1%, 82±3.7% and 96.7±1.7% and for 8&6 were 86±4.0%, 91±3.1% and 98±1.5%, respectively. In conclusion, the altered timeframe of GnRH administration affected EE and tended to affect PR in multiparous beef cows, suggesting that GnRH administration may improve PR when administered 6d, instead of 7d, prior to CIDR removal.