After calving, milk secretion in dairy cows increases rapidly, but the slower rate of increase in feed intake by the cow can lead to a substantial negative energy balance in the animal. Consequently, body tissues, comprising principally of adipose tissue are mobilised and this energy contribution is accounted for in calculating the feeding regime of the animal. In contrast, the extent of body protein mobilisation is considered to be much less but the potential contribution of such to the animal's protein requirements for milk synthesis are neither recognised or exploited in most of the feeding systems used in Europe, including the Swiss ‘APD’ system. The objective of this study was to examine the effect of reducing the calculated supply of absorbed protein on the secretion of milk and milk constituents and whole body energy and nitrogen metabolism in order to quantify any possible contribution of body protein to the nutrition of early lactation cows.