Influence of the development phase of the dominant follicle on the superovulatory response in Nelore heifers

The aim of this study was to evaluate the influence of the dominant follicle during it’s growing, static and regression phases on the superovulatory response in 18 estral cycles of nelore heifers. The follicular development was monitored by ultrasound from Day 6 to Day 10 (Day 0=estrus) of the oestrus cycle, when the diameter of the largest follicle was measured and the number of subordinate follicles counted. The animals where superovulated with 400 or 500IU of FSH/LH twice daily for 4 days begining on day 10 of the oestrus cycle I was injected PGF2a concomitantly with the fifth dose of FSH/LH. Artificial insemination was done 12 and 24 hours after the begining of the estrus. Embryos were recovered on day 6.5 after the first insemination. If a dominant follicle was present before superovulation, it was observed subordinate follicles atretic and low response to superovulatory treatment. The best result of transferable and total embryos was observed when the dominant follicle was in regression phase (3.67 and 10.17) at the beginning of the superovulatory treatment.