EN
Leaving on ovaries a morphologically dominant follicle on the day of start of superovulation significantly lowered its effectiveness in heifers. Mechanical removal of the dominant follicle increased the effectiveness of superovulation. Influence of elimination of a dominant follicle was especially visible in these cases, in which the follicle remained on the ovary during 4 d before the programme started. Significant differences were ascertained in the numbers of corpora lutea found on ovaries on the day of embryo collection and in the numbers of nonfertilized ova.