Most healthy calves killed by coyotes are less than a week old and have been left alone by their mothers. Cows often leave the main herd when they give birth. The newborn calf becomes vulnerable to predators when its mother leaves it to seek food and water. When the cow rejoins the herd or the calf is at least 10 days old, the danger from coyotes is usually over. Just after calving, a cow may be too weak to drive coyotes away from its calf.
Coyotes occasionally kill calves during the birthing process.
In some cases, if coyotes find a cow having a long, hard labor, they may prey upon the calf while it is protruding from the cow, sometimes mutilating the mother in the process. Coyotes may kill a weak and sick calf, especially if the cow is weak and unable to defend it. Calves that have scours or other diseases are especially vulnerable to coyote attacks. Sometimes it may appear that a coyote has killed a calf, but instead it was just feeding on one that died from natural causes. Good animal husbandry practices can help reduce calf losses.