As you probably know, I live on a cattle ranch. Since I know about cattle, I often notice mistakes in books. Here, I’m going to try to help you avoid those mistakes.
The most common mistake is terms used. There is no good unisex name for a single bovine. Most people mistakingly call the animal a “cow” but “cow” is reserved for an older female of the species. If your character is a city kid, he or she may not know this, but if you’re writing about ranchers, you should get these right.
Cow: A female, generally two years of age or older. They’re the ones who produce milk. Keep in mind, they need to give birth to produce milk. Once the calf is weaned, generally at six to ten months, the cow stops producing milk unless someone is milking them. Cows normally have one calf a year. When the calf is old enough, the owners wean it so the cow gets a break before she calves again. Cows are often protective of their calves. Trying to approach a cow with a newborn calf is likely to be more dangerous than approaching a bull. (Our milk cows are accustomed to people around their calves, but the beef cows are not.)
Heifer: A young cow, normally two years or less. (The dictionary says “One who has not borne a calf.”) We also sometimes call calves a “heifer” or “steer” calf if we are specifying gender.
Yearling: Year-old cattle of either gender. They tend to be playful. Bulls of this age aren’t likely to be as aggressive as an older bull.
Bull: An intact male. They weigh around a ton, though it depends on the breed. A ranch has about one bull per 10-20 cows. Bulls can be aggressive toward people. Most ranches try to get rid of the aggressive ones. An injured or tired bull may charge if it doesn’t want to be moved. Most of our bulls are more likely to want fed than to attack a person. Bulls will often fight with each other, which sometimes leads to serious injury.
Steer: A castrated bull. Castration makes them less aggressive than bulls and they don’t have serious fights with other steers. (This generally happens before they are six months old.) It’s rare to see a steer older than two years since they are only used for slaughter, though we sometimes keep one until he’s three because they get huge. (I believe the oxen were steers broke to the plow, but I have no experience with that.) Year-old steers are very curious and playful.
Calf: A baby of either sex, generally under a year old.
I’ll do my best to answer any questions you have about cattle or livestock in general.