Uso de estradiol e GnRH na indução da ovulação em vacas Nelore (Bos indicus) submetidas à IATF com sêmen sexado

Abstract

Aiming to evaluate the efficiency of estradiol cypionate (EC), estradiol benzoate (EB) and estradiol cypionate plus GnRH on induction of ovulation, 383 lactating Nelore (Bos indicus) cows were synchronized and inseminated with sex-sorted semen. Two experiments were conducted to evaluate the follicular dynamics (Experiment 1) and conception rates (CR; Experiment 2). In experiment 1, 39 animals received 2 mg of estradiol benzoate (EB) and a progesterone intravaginal device (P4) on day zero (D0). In day eight (D8), withdrew the device and administered 0,53 mg of prostaglandin (PGF2α) and 300 IU of equine chorionic gonadotropin (eCG). Thereafter the animals were homogeneously allocated in three treatments according the ovulation inducer: EC (1 mg applied in D8); Group EB (1 mg applied in D9) and Group EC+GnRH (1 mg of EC applied in D8 and 8 μg of GnRH in D10, respectively). Ultrasound examinations were performed every 12 hours starting in device withdrawal until the time of ovulation. Statistical analysis was performed with PROC GENMOD and PROC GLM of SAS. The results for EC, EB and EC+GnRH respectively, for the variables maximum diameter of the ovulatory follicle (FO; 12.3±0.3; 11.8±0.5; 12.1±0.4 mm), ovulation rate (92.3%; 92.3%; 100.0%) and moment of ovulation (60.0±2.8; 64.0±2.9; 64.1±3.0h), were similar (P>0,05). In experiment 2, 344 animals were submitted to the same treatments as previously reported and timed inseminated with sex-sorted semen at 60 to 64h after devices withdrawal. No interactions between independent variables (replicate, animal category, body condition score, semen batch and previous use of progesterone device) were observed. There was no effect of treatment on conception rate (EC= 45.2% vs. EC+GnRH= 39.1% vs. EB=34.2%; P=0,09). In conclusion, the association of estradiol cypionate plus GnRH not influenced the follicular dynamics neither the conception rates in lactating Nelore (Bos indicus) cows timed inseminated with sex-sorted semen, showing that is possible to use estradiol benzoate or cypionate as ovulation inducers.