Oestrus cycle of cow is

Oestrus cycle of cows is 18 - 24 days.
The estrous cycle of the cow starts after puberty and occurs approximately every 21 days (18 to 24 days) except for pregnancy, reproductive disease or hormonal disorder.
During estrous cycle, the reproductive tract is prepared for estrus or heat (the period of sexual receptivity) and ovulation (ovum release).