Calves are born around once a year. It's very important they drink their mother's milk within the first few hours. This is a special yellowish liquid known as colostrum that cannot be drunk by humans. It contains numerous antibodies that help the calf to resist diseases. After around five days, the calf will have had enough colostrum and will then drink normal cow's milk for around ten months until it can nourish itself exclusively from grass and other plants.