We care for approximately 250 bison on our ranch. We separate the bulls and the cows every October so we don't risk having late calves the following year. Pregnancy lasts 9 months, similar to humans, and the calves at birth only weigh about 40 lbs. After 6 months the calves can already weigh upwards of 400 lbs and are eating hay and grass along with continuing to nurse from their mothers. We keep the calves with their mothers for up to a year and a half before separating the bull calves from the female herd.
Our bison never have to go far to find food! We supply our animals with high moisture hay, dry hay, essential minerals, and salt/selenium blocks at "free choice" style of feeding. They also pasture graze through the summer months when the grass is tall and lush. Bison are unique in that they know when they are full! There has never been report of a bison overindulging or dying from over eating.