Reproductive Performance of Prepubertal and Pubertal Heifers Submitted to timed Artificial Insemination Protocols

Abstract

This study investigated the effect of using estradiol cypionate (ECP) and equine chorionic gonadotropin (eCG) as part of a hormonal protocol for timed artificial insemination (TAI) on the pregnancy rate (PR) in prepubertal and pubertal Nellore heifers pretreated with intravaginal progesterone (P4). Methods: Two groups of animals were assessed: prepubertal heifers (no corpus luteum (CL) present and follicles<8mm diameter; n=130) and pubertal heifers (CL present; n=94). The beef heifers weighed between 297–320kg and body condition score was 2.3–3.5. On day 0 (d0), all heifers received an intravaginal device containing 0.558g of P4, and 1.0 mg of estradiol benzoate (EB). On d8, the P4 was removed and 0.075mg PGF2300IU of eCG, and 2 mg of ECP were administered. TAI was performed on day 10. Animals that return to show estrous signals post-TAI were re-inseminated (AI) 12h after estrus observation. Animals that returned to estrus after conventional AI were kept with bulls for 45days and after 30days, pregnancy diagnosis was performed. Results: The PR in prepubertal and pubertal heifers were respectively for TAI 29.2% and 37.2% (p>0.05); for conventional AI, 13.0% and 33.9% (P<0.05); and for bulls’ breeding, 36.2% and 35.9%, respectively. (P>0.05). At the end of the breeding season, the PR in prepubertal and pubertal heifers was 60.7% and 73.4% (P=0.062). Conclusion: Use of the hormonal protocol was efficacious for both groups of animals due to the acceleration of puberty and this increased the PR at the beginning of the breeding season