Influence of duration of follicle dominance on embryo quality and fertility of Nelore cows

Abstract

Follicular growth in the cow's estrous cycle occurs in the form of waves, and consists of the following phases: 1) emergence of the follicular wave (FW), in which the follicles present 4 mm in diameter; 2) follicular deviation (FD), with follicles measuring about 8.5 mm diameter in taurine and 6 to 7 mm in zebu; 3) ovulation, in which the dominant follicle reaches an ideal diameter and responds to the pre-ovulatory LH surge. Studies performed especially in Holstein and other Bos taurus females showed a negative effect on the length of the follicular dominance period in oocyte quality, embryo development and fertility. As little has been studied on this subject in zebu, the present study aims to evaluate the impact of ovulatory follicle age on embryo quality and fertility of Nelore cows. Therefore, 680 cows will be submitted to a hormonal protocol for pre-synchronization (D-13 to D-6 = implant of 1 g of P4); 0.530 mg of PGF2±, 300 IU of eCG and 0.5 mg of EC on D-6; 20 ¼g of buserelin acetate (GnRH) and 0.530 mg of PGF2± on D-4. In the first experiment, in order to test the embryo quality, 80 Nelore cows will be distributed into two treatments, after pre-synchronization, with 40 cows per treatment: Trat. FOL-7d - D0 = P4 device (1.0 g) and 2.0 mg EB. On D2 and D2.5 = 0.530 mg of PGF2±; D8 = removal of the device and 0.530 mg of PGF2±; D9.5 = 20 ¼g of GnRH; D10 = FTAI. The FOL-14d treatment will be similar to the previous one, however 2.0 mg of EB on D0 will not be administered. In both, 7 days after FTAI (D17), non-surgical transcervical uterine flushing will be performed for embryo recovery and evaluation. The hypothesis of this experiment is that the prolonged follicular dominance period promotes an increase in the maximum diameter of the dominant follicle and negatively affects the embryonic quality. In experiment 2, to test fertility, 600 cows will be used, divided into three treatments, two of which are similar to experiment 1 (FOL-7d and FOL-14d). A third treatment will be added (FOL-5d), consisting of: D0 = P4 device (1.0 g); D2 = 0.530 mg PGF2± and 2.0 mg EB; D2.5 = 0.530 mg PGF2±; D8 = removal of the device and 0.530 mg of PGF2±; D9.5 = 20 ¼g of GnRH; D10 = FTAI. With this experiment, it is hypothesized that, for both the young and the persistent follicles, there will be a reduction in the fertility of the cows. (AU)