Dinâmica folicular e perfil hormonal em novilhas nelore e murrah pré-púberes submetidas a inseminação artificial em tempo fixo (IATF)

Abstract

The objective of this experiment was to induce puberty, evaluate follicular dynamics and the profile of the hormones progesterone (P4) and estradiol (E2) in pre-pubertal Nelore and Murrah heifers, employing the use of fixed-time artificial insemination biotechnology. We used 6 pre- pubertal Nelore heifers (n = 6) with an average age of 14 to 17 months, weighing 320 kg to 350 kg and 6 pre-pubertal Murrah heifers (n = 6) with an average age of 14 to 17 months, weighing between 422kg to 523kg, duly identified. To select pre-pubertal heifers, an ultrasound was performed to confirm the absence of corpus luteum (CL), ensuring the selection of animals that had not yet started cyclicity. The TAI protocol used consisted of an intravaginal implant with 0.5 mg of progesterone (P4). At the beginning of the protocol (D0), all heifers received the P4 intravaginal device, application of estradiol benzoate (BE) and prostaglandin F2α. On (D7), the implant was removed from the Nelore heifers, and they received estradiol cypionate, prostaglandin F2α and equine chorionic gonadotropin (eCG) intramuscularly (IM). Nelore insemination occurred on (D9), between 48 and 56 hours after removal of the P4 implant. In Murrah heifers, the implant was removed on D9, followed by the application of prostaglandin F2α and eCG via IM. On (D11), the buffaloes received gonadotropin-releasing hormone (GnRH), and insemination was carried out on (D12), approximately 16 hours after the application of GnRH. During the TAI protocol, all heifers underwent blood collection to measure hormone levels of progesterone and estradiol. In Nellore, they occurred on days D7 and D9, while in Murrah, they were performed on days D9 and D12, by puncture of the jugular vein. At the same time, ultrasound examinations were performed to monitor follicular dynamics, monitoring the development of follicles and determining the moment of ovulation, identified by the absence of the ovulatory follicle. The study demonstrated that the mean ovulatory follicular diameter of heifers was 7.83 ± 2.25 mm in Nellore and 7.7 ± 1.63 mm in Murrah, with no significant differences (P>0.05) between species. The diameter of the dominant follicle at P4 implant removal was 6.5 ± 1.59 mm in Nellore and 6.9 ± 4.97 mm in Murrah. The mean progesterone levels were 0.76 ng/mL in Nellore and 1.42 ng/mL in Murrah in the first collection, and 1.00 ng/mL and 0.52 ng/mL, respectively, in the second. Estrogen levels were 9.28 pg/mL in Nellore and 26.75 pg/mL in Murrah in the first collection, and 11.20 pg/mL and 11.59 pg/mL in the second. Although the study did not demonstrate a significant difference in follicular diameter between the two breeds, a difference was observed in reproductive responses. Nellore heifers had an ovulation rate of 100%, while Murrah heifers had only 50%. In addition, Murrah heifers had higher estrogen levels in the first collection. These findings reinforce the importance of adjusting puberty induction and FTAI protocols according to the particularities of each breed, in order to optimize reproductive results.