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.
Young sows can be bred on their first day of fertility while older ones can begin on the next day after checking. 5. In breeding pigs, gestation lasts for about 113 days, so breed the pigs during their fertility periods until pregnancy has been successfully achieved.