Calves then molt annually. F. Care of the Young. Calves may nurse for as long as two years. Some may nurse even longer, if the mother does not have a new calf. The composition of milk remains relatively constant throughout the nursing period.
Nursing usually takes place in the water, but sometimes occurs on ice or land.
Milk is occasionally supplemented with solid pieces of food as early as six months of age. Most calves, however, rely primarily on milk for the first two years. In a zoological environment, calves nurse about six to ten times per day. There is no information available on the frequency of nursing or the volume of milk consumed by a calf in the wild. Cows with calves more than two days old tend to gather in herds separate from the bulls and other females.