In vitro organic matter disappearance of tanniferous browse using rumen liquid from goats ingesting grass versus browse

Abstract

In vitro organic matter disappearance (IVOMD) of African browse species often indicates artificially low nutritive value due to the presence of condensed tannins (CT). Diet of the rumen liquor donor may change this if it contains CT. Leaves from 11 browse species were evaluated for their IVOMD of nitrogen, fibre fractions and CT concentrations. Crude protein (CP) ranged from 14% to 25%, whereas neutral detergent fibre (NDF) varied from 20% to 40%. The CT fractions differed (P ≤ 0.05) among the browse species with most CT either soluble or bound to protein. Acacia brevispica and Berchemia discolor had the greatest concentrations of total CT, whereas Balanites aegyptiaca and Prosopis juliflora had the least. Rumen liquid from goats on grass diet (no CT) or browsing species with CT resulted in differences in IVOMD of NDF (P ≤ 0.05); 37% less (P = 0.11) fibre-bound CT IVOMD resulted when rumen liquid donors consumed browse containing CT. This indicates that (1) during IVOMD assays, rumen fluid donor diets should reflect, as closely as possible, those of the target animals and their diets, and (2) rumen liquid donor diet composition, especially forage CT concentrations, should be documented when evaluating results of IVOMD trials that use rumen liquor donors consuming CT.