Described herein is the use of an aromatase inhibitor (i.e. lezotrole) for synchronizing 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 superovulation from day 1 to day 7 following follicular wave emergence for inducing double ovulation, before dominant follicle selection to improve twinning and in early estrus or mid-diestrus following insemination for improving fertility in a mammal.