Protein and energy relationships in dairy cattle. 1. Dry cows.

Nitrogen metabolism in ruminants is a dynamic process depending on level of intake and composition of dietary dry matter and on the physiological state of the animals. These parameters were analysed in a regression model for the requirements of nitrogen absorbed in the small intestine in relation to nitrogen balance of dry cows fed at maintenance level. The amount of total dietary nitrogen and the apparent nitrogen digestibility vary notably according to energy intake and energy concentration in dietary dry matter. On the contrary, the amount of nitrogen absorbed in the small intestine is only slightly affected by these parameters. The discrepancy between these statements lies mainly in differences in intestinal nitrogen absorption and in altered fermentation processes of the large intestine in response to changes in energy supply and ME concentration in dietary dry matter.