Estrous Behavior in a Group of Cows.
Cows are bisexual when in estrus (cows mount cows, bulls mount cows, and bulls mount bulls). The primary sign of estrus is standing to be mounted. The cows doing the mounting like the Jersey cow in the picture need not be in estrus herself, however, cows that are coming into heat and those that have just been in heat are more likely to participate in group activity.
Drost M (1974)