The present study analyzed the physiological significance of the dominant follicle (DF) and its removal on the superovulatory response of 42 Nellore cows and tested the hypothesis that the number of subordinate small follicles (3-8mm) could be used as a single criterion for the evaluation of the presence or absence of a DF in the ovaries. Ultrasonographic examinations were performed two days before the beginning of superovulatory treatment (D0) and the cows divided into three groups: group without DF (NDF), group with a DF (DF) and group with an aspirated DF (ADF). The superovulatory response of the donors did not differ between groups, but the rate of embryonic viability was higher in NDF (69.40%) and ADF (68.99%) groups compared to DF (48.54%). The number of unfertilized structures did not differ between NDF and DF or between NDF and ADF groups, but was higher in DF compared to ADF. It is concluded that, in Nellore cows, the number of subordinate follicles is a safe criterion for the evaluation of the presence of a DF in the ovaries, but errors could be avoided if only 4-8mm follicles were considered, and that the presence of a DF at the beginning of superovulation reduced the embryonic viability rate and its removal by transvaginal aspiration guided by ultrasound induced embryonic viability rates similar to that observed in the absence of a DF.
Bovine; Nellore; dominant follicle aspiration; superovulatory response
