Evaluation of the 7 & 7 Synch and 7-day CO-Synch + CIDR protocols for estrus synchronization of beef cows prior to fixed-time artificial insemination with conventional or sex-sorted semen

Abstract

An experiment was designed to compare the recently developed 7 & 7 Synch and the 7-day CO-Synch + CIDR protocols for synchronization of estrus among beef cows prior to fixed-time artificial insemination (FTAI) with conventional or sex-sorted semen. Bos taurus cows (n = 1538) were blocked based on age and days postpartum (DPP) and randomly assigned to protocol and semen type. Cows treated with the 7-day CO-Synch + CIDR protocol (n = 769) received administration of gonadotropin-releasing hormone (GnRH; 100 g gonadorelin) and insertion of a 1.38 g intravaginal progesterone releasing insert (CIDR) on Day -10, and administration of prostaglandin F2 (PG; 500 g cloprostenol) coincident with CIDR removal on Day -3. Cows treated with 7 & 7 Synch (n = 769) received PG and insertion of CIDR on Day -17, GnRH on Day -10, and PG coincident with CIDR removal on Day -3. Estrus detection aids (Estrotect) were applied to all cows on Day -3, and activation status was recorded at FTAI. Cows received FTAI 66 h after CIDR removal with either conventional (20 x 106 cells per unit) or sex-sorted (4 x 106 cells per unit; SexedULTRA 4M) semen. A greater proportion of cows expressed estrus (P = 0.01) prior to FTAI following 7 & 7 Synch (82%; 629/769) compared with the 7-day CO-Synch + CIDR (64%; 492/769). Estrus expression was also affected by protocol x DPP (P = 0.0004), with 7 & 7 Synch resulting in a greater increase in the proportion of cows expressing estrus prior to FTAI among cows with greater DPP. Across protocols, body condition score (BCS) affected (P = 0.05) estrus expression, with greater proportion of cows expressing estrus prior to FTAI at greater BCS. Sex-sorted semen resulted in reduced (P < 0.0001) pregnancy rates to FTAI. Irrespective of semen type, greater (P = 0.001) pregnancy rates to FTAI were obtained among cows treated with 7 & 7 Synch (conventional semen: 72% [280/389]; sex-sorted semen: 52% [199/380]) compared with the 7-day CO-Synch + CIDR (conventional semen: 60% [231/383]; sex-sorted semen: 44% [171/386]). In summary, 7 & 7 Synch resulted in an increased proportion of cows expressing estrus prior to FTAI and an increased pregnancy rate to FTAI with conventional and sexed semen. With these results and ease of application, 7 & 7 Synch offers potential as a platform to improve success with fixed-time AI in beef cows.