Described herein is the use of an aromatase inhibitor (e.g. lezotrole) for synchronizing ovulation (i.e. follicular wave emergence, ovulation) in a herd or a single mammal. Also described is the use of said aromatase inhibitor at the beginning of a follicular wave emergence for inducing multiple ovulation or improving the response to ovarian superstimulation. Treatment with aromatase inhibitor early in the follicular wave will induce follicular co-dominance and increase the incidence of double ovulation and twin pregnancy. Aromatase inhibitor treatment may be used before or soon after insemination (early estrus to early diestrus) for improving fertility in a mammal.
