This experiment was carried out to verify the effect of the administration of different doses of GnRH (buserelin) analogue on the emergence of a new follicular growth wave and the number of recruited follicles from this wave, accessory corpus luteum formation, the dominant follicle diameter and the spontaneous corpus luteum on the luteolitic administration day and subsequent synchronization rate and the interval between the PGF2α application and the estrus manifestation. Twenty crossbreed female cattle in diestrus, crossbred Holstein x Zebu and Simental x Zebu were allotted to four treatment groups, each containing five animals. In the treatment 1 the animals received 4 mg IM. of buserelin at day 0 (day in which the treatment began) and 150 mg of D (+) Cloprostenol at day 6. In treatments 2, 3 and 4, the animals received 6, 8 and 10 mg of buserelin, respectively, by the same application way, and 150 mg of D (+) Cloprostenol at day 6. The ovarian activity was daily monitored, with the help of an ultra-sound machine, from day 0 to estrus or until day 11 on those animals, which did not answer to prostaglandin. The application of 8 or 10 mg of buserelin at an unknown phase of diestrus, in female crossbred cattle, promoted an emergence of a new follicular growth wave faster than the applications of 4 or 6 mg of the same hormones, while the other evaluated parameters did not differ among treatments.
follicular dynamic; buserelin; cloprostenol; estrus synchronization; cattle
