The effect of different doses of hCG administration on the emergence of a new follicular growth wave and the number of recruited follicles from this wave, the accessory corpus luteum formation, the diameter of the dominant follicle and of the spontaneous corpus luteum on the day of a luteolitic administration and subsequent synchronization rate and the interval between the PGF2α administration and the estrus manifestation were evaluated. Twenty crossbred female cattle in diestrus, divided in four treatments containing five animals each were used. In treatment 1, the animals received 500 IU IM of hCG on day 0 (day which started the treatment) and 150 μg of D(+) Cloprostenol on day 6. In treatments 2, 3 and 4, the animals received 1000, 2000 and 3000 IU, respectively, on day 0 and 150 μg of D(+) Cloprostenol on day 6. The ovarian activity was monitored daily, with the help of an ultra-sound apparatus, from day 0 to the estrus, or up to day 11 after the treatment on those animals which did not response to prostaglandin. There were no significant differences among the effects of 500, 1000, 2000 and 3000 IU of hCG on the follicular dynamic, synchronization rate and the interval between the PGF2α and the estrus manifestation. There was, however, a tendency of 2000 and 3000 IU doses to induce an emergence of a new follicular growth wave faster than 500 or 1000 IU of these hormones.
follicular dynamic; hCG; Cloprostenol; estrus synchronization; cattle
