The Use of 5-d CO-Synch+CIDR and 7-d EB+CIDR Synchronization Programs in Nellore Females
Reproductive performance of heifers and cows submitted to either the 5-d CO-Synch+CIDR or 7-d EB+CIDR program was evaluated. Nellore females (n = 411) were used (nulliparous, n = 198; primiparous, n = 80; multiparous, n = 133). The 5-d CO-Synch+CIDR program consisted of insertion of a CIDR and 100 μg of GnRH (Fertagyl®) on d 0. On d 5, CIDR was removed and two doses of 25 mg PGF2α (PGF; Lutalyse®) were administered 6 h apart. Timed-AI was performed on d 8 (72 h after CIDR removal). The 7-d EB+CIDR program consisted of insertion of a CIDR and 2 mg estradiol benzoate (EB) on d 0. On d 7, CIDR was removed and 25 mg of PGF, 0.6 mg of estradiol cypionate (ECP®) and 150 IU of eCG (Novormon®) administered. Timed-AI was performed 55 h after CIDR removal. Estrotect®patches were applied at CIDR removal and visual estrus detection performed on a 12 h interval for the following 96 h. Blood samples for progesterone (P4) analysis were collected 10 d after AI to confirm ovulation. Concentration of P4 was assessed by chemiluminescent immunoassay. Data were analyzed using the GLIMMIX and MIXED procedures of SAS. Estrus response was greater (P < 0.05) in 7-d EB+CIDR than the 5-d CO- Synch+CIDR program (nulliparous, 95.8 vs. 66.0%; primiparous, 48.7 vs. 0.0%; and multiparous, 76.9 vs. 13.4%, respectively). In contrast, ovulation rate (89.8 %) was similar between programs. Concentration of P4 10 d post AI was greater (P < 0.05) in primiparous and multiparous cows in the 7-d EB+CIDR than 5-d CO-Synch+CIDR program (6.8 vs. 4.9 ng/mL; and 6.9 vs.5.8 ng/mL, respectively); but did not differ between treatments in nulliparous females (4.4 ± 0.14 ng/mL). Timed-AI pregnancy rate was greater (P < 0.05) in multiparous cows (58.4 vs. 32.8%), but did not differ for nulliparous (51.0 vs. 41.0%) and primiparous, (25.6 vs. 31.7%) for the 7-d and 5-d program, respectively). The 7-d EB+CIDR program resulted in a greater number of females in estrus, and either greater or similar P4 on the subsequent estrous cycle and timed-AI pregnancy rates. In conclusion, reproductive performance seems to be enhanced with the 7-d EB + CIDR in comparison to the 5-d CO-Synch+CIDR program in Nellore females.
Keywords: Nellore, 7-d EB-P4, 5-d CO-Synch