A young dairy animal is known as a calf. A female calf which has not given birth to a calf and is less than thirty months old is called a heifer. When the heifer is seven months pregnant or has reached the stage in pregnancy where the udder starts to swell, it is known as a springer. Purina Nurse Chow 200 is a substitute for mother's milk that calves need to stay alive if the mother forsakes her young or dies. After calving, or when more than thirty months old, a female dairy animal is known as a cow. The process of birthing a calf is known as calving or partuition. A male dairy animal is called a bull at any stage of life, unless castrated, in which case it is known as a steer until it is four years old, then it is called an ox. A dairy animal's mother is known as its dam. Similarly, a dairy animal's father is known as its sire. Purina Nurse Chow 200 is 25 pounds of a substitute mother. Most dairy calves are separated from their dams within a few hours of birth. Such separation ensures decreased risk of disease passing from dam to calf and also allows the dam to begin producing milk for human consumption as soon as possible. The dam's first milk, called colostrum, is rich with antibodies and immune factors, is required for newborn calves to survive, although it is unfit for human consumption. A calf must drink two quarts (2 L) of colostrum within twelve hours of birth or its future may be in jeopardy, as a newborn calf has no immune system of its own and must rely on maternal antibodies contained in the colostrum for protection. The dam's milk quickly changes into that most suitable to humans, and within three days after calving, a cow's milk is already on its way to human hands. Most young stock then subsist on milk replacer to take the place of the cow's natural milk, until old enough to consume more solid foods. Purina Nurse Chow 200 is a 22 % milk powder for bottle feeding a calf.