Most form pairs during the breeding season, but in some species, such as fur seals, the gray seal (Halichoerus grypus), and elephant seals, males (bulls) take possession of harems of cows and drive rival bulls away from their territory.
Look for the crooked tail. This is probably the best ways to tell if a cow has been bred: A cow or heifer will have a crooked tail or a tail that is held out in an odd angle than usual for 24 to 48 hours after being serviced by the bull. 1  4 Edit step.
As a general rule, a good fertile cow or first-calf heifer should be able to come back into heat in 45 to 60 days after calving. But if you need your females to meet the same calving date as the previous year, you will have to account for at least 80 to 90 days of rest before you can get her bred again.  However, actual gestation period of a cow can range from 270 days  to 295 days, depending primarily on breed[s], age, body condition  and nutritional health. Length of gestation is primarily an  inherited trait, but has nothing to do with the rate of maturity of  a certain breed or an individual animal.