Because of the continuing increase in the number of cows in dairy herds, it is increasingly difficult for the herd manager to observe and control individual cows in his herd. Systems which can automatically watch over production and health in large dairy herds are required. Production control is a long-term process and for this purpose production data have to be collected in a suitable form. Health control can be realized by a system measuring and reporting deviations from the normal health status of each cow, so that preventative measures can be taken. Such a system would inevitably make use of those physiological variables which can be measured and recorded quickly and automatically at each milking.