Protein nutrition affects feed intake in dairy cows

Abstract

An increase in protein content of dairy cow diets is often associated with an increased feed intake, however the magnitude of these answers and the mechanisms involved are still not well understood. This review characterizes the effects of nitrogen and protein content of the diet on feed intake in dairy cows and discusses the various hypotheses concerning their mechanisms. The supply of degradable nitrogen to the microbial population and the availability of protein for milk synthesis affects dry matter intake. These effects can be quantitatively important and generally increase with time. If the role of degradable nitrogen on microbial activity explains largely the feed intake increase, the action of proteins on the regulation of intake is less easily explained and could be multi-factorial. Similar to monogastric animals, possible modifications of the amino acid balance could also modify the control of feeding behaviour and explain the short-term intake effects. However, the increase in time of the feed intake responses to proteins militates more for indirect action via, for example the energy demand or the mobilization of the reserves, than for direct protein action on feed intake control. The response law to protein content and a better understanding of the mechanisms involved could be helpful in incorporating the effects of protein nutrition into the models of feed intake prediction.