Dinâmica folicular e qualidade de embriões de novilhas girolando submetidas a protocolos de inseminação artificial em tempo fixo

Abstract

The study evaluated the ovarian follicular dynamics during the natural estrous cycle and after two hormonal protocols aiming at Fixed Time Artificial Insemination (FTAI) of Girolando heifers, besides the quality of the embryos coming from such protocols. The experiment consisted of two stages: the first one consisted of daily ultrasonographic evaluations of 30 heifers, in a period of 30 days; and the second consisted in evaluating the follicular dynamics of the same heifers submitted to two FTAI protocols, besides the evaluation of the embryos coming from such protocols. Thirty Girolando heifers were used, allocated in two treatments: T1 (n = 15) heifers submitted to the protocol consisting of maintenance a progesterone implant (P4) for 9 days (9d) were used, with insertion of the third use implant (previously used for 18 days) on the first day of the protocol (D0) and 2 mg of intramuscular Estradiol Benzoate. Then, after 7 days, 150g PGF2 was given; on the ninth day after the start of the protocol the implant were withdrawn and 1 mg of intramuscular Estradiol Cypionate (EC) was administered and, at the end, on the eleventh day, FTAI was given; In T2 (n = 15) heifers were submitted to the 5dCO-Synch + Progesterone Implant protocol, receiving in D0 the intravaginal implant of P4 of third use (previously used for 18 days) and 100g intramuscular GnRH. After five days the implants were removed and 150g intramuscular PGF2 was administered; on the sixth day the 150g dose of intramuscular PGF2 was repeated, on the eighth day 100g of GnRH was administered and made the FTAI. Seven days after the inseminations the heifers of both groups were submitted to uterine washes, for the collection of the embryos. Ultrasound examinations were performed daily from D0 until the day of ovulation, according to the experimental group. During the natural estrous cycle, heifers presented cycles characterized by two (6/11) or three follicular waves (5/11), with a mean duration of 21.66 ± 1.36 and 22.40 + 3.36 days respectively. For heifers with two follicular waves, the first wave had a mean duration of 18.33 + 3.32 days, with a maximum dominant follicle diameter of 14.05 + 2.16 mm, with growth and regression rates of 1.20 + 0.42 mm and 0.93 + 0.17 mm per day, respectively. The second wave had a mean duration of 10.33 ± 2.65 days, with a maximum dominant follicle diameter of 14.68 ± 2.23 mm, which differed (P <0.05) between animals with two and three follicular waves, and growth rates of 1.08 ± 0.33 mm/day until ovulation. For heifers with three follicular waves, the first wave had an average duration of 17.0 ± 1.87 days, and the diameter of the dominant follicle was 13.70 ± 1.45 mm, with a growth rate of 1.00 + 0.14 mm/day, and later regression rate of 1.1 + 0.37 mm/day. In the second follicular wave, the duration was 12.2 + 2.38 days, with a follicle with a maximum diameter of 11.22 + 1.21 mm, thus providing a growth rate of 0.94 + 0.19 mm/day and, regression rate of 1.04 ± 0.60 mm/day. In relation to the third follicular wave, the mean duration was 8.60 + 4.03 days, with a maximum diameter of 13.26 + 1.74 mm, with a daily growth of 1.30 + 0.36 mm until ovulation. For the follicular dynamics in the FTAI 12 protocols, for T1 and T2, respectively, the follicle diameter in the D0 was 12.01 + 3.17 mm and 12.79 + 3.33 mm, the follicle diameter on the second day after the insertion of the implant P4 (D2) of 11.29 ± 3.23 mm and 8.29 + 3.58 mm, follicle diameter on the day of the artificial insemination of 11.25 ± 3.88 mm and 12.82 ± 3.13 mm and preovulatory follicle diameter of 13.67 ± 3.65 mm and 13.47 ± 2.35 mm. The interval from implant withdrawal to ovulation was 70.67 + 15.33 hours and 105.60 + 16.24 hours, and result of volumes to luteal bodies on the seventh day after ovulation of 3.97 + 1.81 cm³ and 3.96 ± 1.89 cm³, differing (P <0.05) between treatments in relation to follicle diameter in D2, follicle diameter on the day of artificial insemination, and hours from implant withdrawal to ovulation. The estrus and ovulation rates were 90% and 48.3% and 65% and 83.3% for T1 and T2, respectively. The embryo quality did not differ (P> 0.05) between the treatments, having diameters after collection of 0.18 + 0.25 m and 0.11 + 0.035 m, respectively, after fixation in paraformaldehyde (mm³) of T1 = 0.002 + 0.0005, and T2 = 0.002 + 0.0007, total cell numbers of T1 = 54.00 + 13.91, and T2 = 65.33 + 27.11, and number of apoptotic cells of T1 = 9.47 + 7.03 and T2 = 13.39 + 5.55. However, in relation to the follicular dynamics of the animals in natural estrus, the only difference found was the diameter of the dominant follicle in the second wave among heifers that have two or three follicular waves. In relation to the hormonal protocols that alter the duration of proestrus, they imply changes in the follicular diameter of the Girolando heifers, and the increase in the duration of proestrus implied an increase in the interval between the withdrawal of the progesterone implant from estrus and ovulation, which may hinder the programming of inseminations in fixed time, but did not modify the quality of the embryos. GnRH applied at the time of artificial insemination increases the ovulatory rate in FTAI protocols. Treatment with EC at the end of the hormonal protocol induces high estrus, but without correspondence in the ovulatory rate.