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.
1 Cows should be bred 45 to 80 days after they have calved, depending on age and condition. 2  The optimum bull-to-cow ratio is 1 bull per 10 to 30 cows, depending on the size of the pasture, and the bull's age, promiscuity/libido and experience. Bulls reach peak fertility by 20 months of age, after 20 months of age it can only drop, barring illness or injury, with proper nutrition most bulls fertility will not start to decline until after 6-7 years of age.