Models of suppressive effect of tannins. Analysis of the suppressive effect of tannins on ruminal degradation by compartmental models

Three compartmental models were developed to evaluate the suppressive effects of tannins on the extent and rate of degradation of tree foliage. The first model was based on the assumption that tannins modify the parameters of the degradation kinetics, the second was based on the assumption that tannins bind material, independent of the basic degradation kinetics, and the third combined these two assumptions, i.e., that tannins both suppress degradation and bind free material. Degradation was measured by suspending the samples in dacron bags in the rumens of goats, with or without the inclusion of polyethylene glycol (PEG). It was assumed that PEG annuls the suppressive effect of tannins on degradation of plant components, and hence that the difference between the curves that describe degradation with or without PEG indicates the suppressive effect of tannins present in the foliage. The data on the observed degradation of dry matter, neutral detergent fibre and protein, in four typical Mediterranean forest tree species were fitted by these models. It was found that the combined model fits the data better than either of the other two models. Increasing content of tannins in the foliage was associated with an increase of the bound free material and a decrease in the degradation rate of the degradable matter, but not with an increase of the non-degradable fraction.