A NONLINEAR COMPARTMENTAL MODEL TO DESCRIBE FORAGE DEGRADATION KINETICS DURING INCUBATION IN POLYESTER BAGS IN THE RUMEN

A new model for describing forage degradation kinetics during incubati on in the rumen using polyester bags is presented. Attention is given to dealing with the problem of deviations from exponential behaviour i n the early stages of degradation by devising a function capable of re presenting exponential or sigmoidal trends. This is achieved by allowi ng part of the fractional degradation rate to vary with time of incuba tion, thus enabling responses other than those expected under simple f irst-order kinetics to be described. Seven sets of data consisting of 620 curves were analysed to study the performance of the new model com pared with a commonly used exponential model. The proportion of signif icantly better fits varied from set to set. The new model deals succes sfully with sigmoidal behaviour and, thus, provides a means of analysi ng the degradation profiles of low-quality forage feeds.