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.
Cattle are bred at the age of 15 months, and have their first calf at 2 years of age, at which time they begin to produce milk. Dairy cows are not slaughtered until they are too old to produce milk, which at our farm is usually after at least 5 lactations (or a little more than 5 years).