Influence of equine (eCG) and human (hCG) chorionic gonadotropins on corpus luteum development and pregnancy rate in bovine embryo recipients

Abstract

The aim of this study is to evaluate the effects of equine (eCG) and human (hCG) chorionic gonadotropin (hCG) administration in ovulation synchronization protocols for fixed-time embryo transfer (FTET) on area and blood flow (BF) of the corpus luteum (CL), progesterone concentration, pregnancy/FTET and pregnancy loss in embryo recipient cows. In Experiment 1, the objective is to evaluate the effects of hCG at doses of 500, 1000 and 2000 UI on the size and BF of the CL, formation of accessory CL and on the plasma concentration of progesterona. For this, 60 non-lactating Nellore multiparous cows will be used in two replicates and will receive 12.5 mg of dinoprost tromethamine, only females that ovulate spontaneously will enter, being equally separated into four experimental groups (10 animals per group) two days after ovulation: Control Group, G500, G1000, G2000 (no additional treatment, 500 IU, 1000 IU and 2000 IU of hCG, respectively), being evaluated every 48 hours for 14 days in relation to CL size and PS, in addition to concentration plasma of progesterone. In experiment 2, 800 Nelore or crossbred embryo recipient cows (F1 - Nelore x Angus) will have their ovulation synchronized based on the following protocol, considering the day of expected estrus as D0: D-11 with 2 mg of benzoate estradiol and device insertion of P4, D-4 with 12.5 mg dinoprost tromethamine F2± and D-2 with 1 mg estradiol cypionate. The females will be assigned to four groups (200 animals per group), namely: Control Group (300 IU of eCG on D-2); eCG/split group (150 IU eCG on D-4 and 150 IU on D-2); hCG group (hCG on D3); eCG/divided+hCG Group (association of eCG and hCG Group treatment), and the dose of hCG will be defined according to the results obtained in Experiment 1. At the time of embryo transfer, all females will be evaluated and only those that have CL will have a transferred embryo, evaluating the area and BF. Approximately 25 and 50 days after the transfer, pregnancy diagnoses will be performed to assess pregnancy and pregnancy loss. For statistical analysis, continuous variables will be analyzed by ANOVA using PROC MIXED, and for dependent variables with binomial distribution, the GLIMMIX procedure will be used.