Ovarian follicular dynamics of Nelore (Bos indicus) cows subjected to a fixed-time artificial insemination protocol with injectable progesterone

Resumo

This study aims to evaluate ovarian follicular dynamics of Nelore cows subjected to fixed-time artificial insemination (FTAI) with injectable progesterone (P4) or intravaginal device. In the device group, 20 cows received an intravaginal device with 1 g P4 and administration of 2 mg estradiol benzoate (EB) intramuscularly (im) on D0. The device was removed on D8, followed by administration of 500 ?g cloprostenol, 300 IU equine chorionic gonadotropin (eCG) and 1 mg estradiol cypionate (EC), im. The cows were inseminated 48h later. In the injectable group, 350 mg P4 (300 mg subcutaneously and 50 mg im) and 2 mg EB im were administered on D0 to 16 cows. On D6, 500 ?g cloprostenol, 300 IU eCG and 1 mg EC were administered im. The FTAI was performed 48h later. Sixty-five percent of cows from the device group (13/20) and 75% from the injectable group (12/16) showed follicles ? 5 mm on D4 (p>0.05). The average rate of follicular growth was 0.92±0.25 mm/day for the device group and 1.06±0.45 mm/day for the injectable group (p>0.05). The average diameter of the dominant follicle (DF) at FTAI was 11.4±1.4 mm for the device group and 10.8±1.8 mm for the injectable group (p>0.05). In the device group, ovulatory follicles (OF) had an average diameter of 12.1±1.4 mm, and in the injectable group 12.3±1.6 mm (p>0.05). Ninety percent of the device group (18/20) and 37.5% of the injectable group (6/16) demonstrated ovulation (p<0.05). The average diameter of the corpus luteum (CL) was 18.7±4.3 mm for the device group and 17.7±3.6 mm for the injectable group. The injectable P4 showed similarity in the presence of follicles ? 5 mm on D4, follicular growth rate, diameters of the DF, OF and CL. However, the ovulation rate was higher in the device group.