CamDairy is a computer model designed to help farm advisers, farmers, students and research scientists who are interested in the nutrition of dairy cows. It can be used to predict milk production from information describing the physiological status of cows and the feeds offered to them. This is a valuable way of identifying constraints to production. In addition, the program can be used to devise rations that maximize profit, taking into account information provided about the cows, the feeds available, feed costs and milk returns. This is a valuable means of testing the possibility of improving current feeding practices.