Calves on average weigh around 60 - 100 pounds at birth. Within an hour of birth, the calves are able to stand, walk and nurse. The first milk produced by cows are known as colostrum. They are very important to the calves as they contain vital nutrients as well as antibodies for the calf's well being. Calves must be kept a minimum of 48 hours with their mothers to ensure they have sufficient colostrum.
For dairy calves, they are usually kept with their mothers for few days to ensure they receive sufficient colostrum and protein from the milk. After this, the calves are weaned by removing them from the pastures in which their mothers are kept. They are moved to areas where their mothers can't see or hear the calves. Commercial milk replacers, usually in the form of powder mixed with water, are then fed to the calves using a bottle or pail. Calves are able to start eating grass at approximately 2-4 weeks of age. After that, they can be moved completely onto a good quality pasture and receive adequate nutrition.
Beef calves are heavier at birth compared to dairy calves. They drink about 1 gallon of milk per day. They are weaned when they are approximately 6-10 months old. At this time, they will weigh about 450 pounds or more. Young calves will then enter the stocker and backgrounder phases, in which they are left in open fields to graze at will and gain weight. Males and females may be sent to auction, where they will purchased by stockyards and feed lots for final weight gain before being slaughtered. As for females, they may be retained by the farmers for future breeding.
Veal calves are usually Holstein calves. The main reason being Holsteins are dairy breeds, so the female calves are being kept for future milk production, whereas the male calves are sold at birth for veal products. Newborn veal calves are called bobs and they may be slaughtered any age between birth to age 3 weeks for their meat. Milk fed veal calves have low-iron diet to produce white meat. As for "free range" veal calves, they will stay with their mothers, feed on her milk and roam freely in large pastures before being slaughtered at 24 weeks.