There are boy cows and girl cows. Boy cows are called bulls unless they have been castrated in which case they are called steers. Girl cows before they have had a baby are called heifers. Ones that have had one or more babies are called cows. Young cattle are called calves until they are weaned, then weaners until they are a year old in some areas, in other areas they may be known as feeder calves or simply feeders. After that, they are referred to as yearlings.