Recombinant Bovine Somatotropin in synchronization of ovulation in Tabapuã females

Abstract

This study aimed to evaluate the effect of Bovine Somatotropin (bST) administration on ovulation, ovulatory follicle diameter, ovarian diameter and number of follicles larger than 2 mm in cows of the Tabapuã breed after synchronization of ovulation with progestogen. Cows (n=16) received an auricular implant of progestogen and 1 mg estradiol benzoate (IM) at a random stage of the estrous cycle (Day 0). On Day 5, coinciding with the emergence of the follicular wave, the females were divided into two groups: G-I (control, n=8) and G-II (treated, n=8). G-II received 500 mg bST subcutaneously in the region between the ischium and tailhead. On day 10 the progestogen was removed concomitantly with the administration of 500 g of PGF2 and 300 g GnRH to cows with follicles larger than 9 mm. From the day of the GnRH application until ovulation the animals were evaluated by ultrasonography (every 12h on average) to determine the moment of ovulation, ovulatory follicle diameter, ovarian diameter, and number of follicles larger than 2 mm. No treatment effect on timing of ovulation, ovulatory follicle diameter, diameters of the ovaries and number of small follicles (2 to 4 mm) was detected. The administration of 500 mg bST at the time of follicular emergence do not affect follicular development or timing of ovulation in Tabapuã cows.