166 Comparison of the 7 and 7 Synch protocol and the 7-day CO-Synch + controlled internal drug release protocol among recipient beef cows in an embryo transfer programme

Abstract

An experiment was designed to evaluate the effectiveness of the recently developed 7 and 7 Synch protocol to synchronise oestrus and ovulation among recipients before embryo transfer (ET). Postpartum beef cows (n=1358) across 13 locations were assigned to either the 7-day CO-Synch + controlled internal drug release (CIDR) protocol or the 7 and 7 Synch protocol before oestrus detection and subsequent ET. Cows were pre-assigned to balanced treatments within location based on age and days postpartum, and body condition score was recorded at ET. Cows assigned to the 7-day CO-Synch + CIDR protocol were administered gonadotrophin-releasing hormone (GnRH; 100µg of gonadorelin acetate) on Day 0, an intravaginal CIDR insert (1.38g of progesterone) from Day 0 to 7, and prostaglandin F2α (PG; 25mg of dinoprost tromethamine) coincident with CIDR removal on Day 7. Cows assigned to the 7 and 7 Synch protocol were administered PG (25mg of dinoprost tromethamine) coincident with CIDR insertion on Day −7, GnRH (100µg of gonadorelin acetate) on Day 0, and PG (25mg of dinoprost tromethamine) coincident with CIDR removal on Day 7. The 7 and 7 Synch protocol was hypothesised to enhance response to GnRH administration on Day 0 among mixed groups of oestrous cycling and anestrous cows, ultimately resulting in improved oestrous response and synchrony of oestrus before ET. Cows were observed for visible signs of oestrus following oestrus synchronisation, with GnRH (100µg of gonadorelin acetate) administered to cows failing to express oestrus during the detection period. Length of the detection period varied among locations but was consistent across treatments within location. Embryo transfer was performed approximately 7 days after oestrus or GnRH administration. Presence of corpora lutea (CL) was determined via transrectal palpation by a single veterinarian blinded to treatment, and embryos were transferred only to cows with palpable CL. Embryo transfer was performed using fresh or frozen embryos staged and graded according to IETS recommended guidelines, with embryo information recorded for each recipient. Data were analysed using the PROC GLIMMIX procedure of SAS (SAS Institute Inc.). Proportion of cows expressing oestrus was improved (P<0.0001) among cows assigned to the 7 and 7 Synch protocol (86% (529/615) vs. 76% (488/640)). The proportion of recipient females with palpable CL tended to be greater (P=0.07) among cows assigned to the 7 and 7 Synch protocol (82% (478/586) vs. 80% (451/565)). Among cows that expressed oestrus, a greater proportion (P<0.01) had palpable CL following the 7 and 7 Synch protocol (88% (466/529) vs. 86% (418/488)). Consequently, irrespective of embryo type received, the proportion of recipients pregnant to ET was greater (P<0.01) following the 7 and 7 Synch protocol (39%; 263/668) compared with the 7-day CO-Synch + CIDR protocol (33%; 228/690). In summary, the 7 and 7 Synch protocol improved the likelihood of oestrus expression in recipient cows, increased the proportion eligible to receive an embryo, and resulted in greater pregnancy rate to ET.