This research has the scientific challenges to compare the morphological, molecular and functional changes of the corpus luteum (CL) from cows treated with eCG before or after ovulation. Also, as compare the reproductive efficiency of these two treatments. Therefore, we will perform two experiments. The first experiment with dynamic ovarian ultrasound (B mode and color Doppler), serum profiles of estradiol and progesterone, the estrous cycle duration and corpus luteum biopsy for histologic analysis and sequencing of mRNA after treatment (Experiment 1; n = 54). And the second experiment, with reproductive efficiency through pregnancy per artificial insemination (P/AI) and embryo mortality of dairy cows (Experiment 2; n = 900). All females will be submitted to a follicular wave and ovulation synchronization protocol of 10 days. At random days of the estrous cycle (D-10) will be used intravaginal devices containing 1.9 g of P4 (iP4) and intramuscular (IM) injection of 2 mg of estradiol benzoate (EB). Seven days later, D-3, 25 mg of PGF2± IM will be administered, at which time the animals will be divided among three proposed treatments: 1/3 animals receive 400 IU eCG IM (D-3; Group eCG-pre); 1/3 of the animals receive 400 IU eCG IM 3 days after estrus (D+3; Group eCG-post); or 1/3 of the animals that did not receive any treatment (Group Control). Eight days after the beginning of the synchronization protocol, D-2, the iP4 of all cows are removed and the animals receive the application 1.0 mg of estradiol cypionate IM (EC). In Experiment 1, the day of estrus will be considered the D0 of the estrous cycle and in Experiment 2 D0 will be the day of timed AI.
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