The effects of underfeeding on digestion in ruminants

Abstract

The negative relationship between intake and digestibility of a same diet has been widely described. The review of the different processes of ruminal digestion shows that the main cause of the variation in digestibility is the retention time of particles in the rumen. However, most experiments have been carried out at levels of intake higher than maintenance. For this reason, a special attention is paid to experiments carried out at low levels of intake. In these conditions, the response of digestibility to a decrease in intake is variable : it can increase, be stable or decrease. Up till now, it has not been possible to determine the animal or nutritional (forage, nutritive value…) factors which influence the way of variation, and especially the unexpected decreases in digestibility. However, it has been clearly shown that these decreases are not due to an insufficient retention time of particle in the rumen, or to an insufficient reduction of particle size. Differences in microbial activity have not been exhibited by in situ measurements. It is hypothesised that a reduction of bacterial growth due to limiting factors, or of the expression of microbial degradation potential, occurs at very low intakes.