Abstract

This paper reviewed the effect of tannin on intake, digestibility, fermentation and methane production of various tropical browses. Under communal production system in Africa, ruminants have free access to trees and shrubs throughout the year especially, in dry season. These browse contains high nitrogen in addition to tannins that can suppress rumen methanogenesis. Hydrolysable and condensed tannins and their extracts have been shown to decrease methane (CH₄) production under both in vivo and in vivo conditions. The molecular weight is a key factor for its effect on digestive enzymes and microbes in the rumen. Low molecular weight tannins could be more effective inhibitors of microbes, including methanogens, compared with high molecular weight tannins. Consumption of low to moderate concentrations of tannins did not affect voluntary feed intake, while high tannin concentrations resulted in reduced intake. The effect of tannins on protein degradation is a reduction in the immediately degradable fraction and fractional rate of degradation. Thus a systematic evaluation is needed to determine optimum levels of supplementation in a mixed diet in order to attain a maximal depressing effect on enteric CH₄ production with a minimal detrimental effect on rumen fermentation of poor quality roughage based diet. Therefore, more in vivo studies for tannin rich plants and their extract should be conducted with hydrolysable tannins since they appear to be more promising.

Keywords: Browses; Digestibility; Intake; Methane; Reduction

Abbreviations: CH4: Methane; GHG: Greenhouse Gasses; CO₂:Carbon Dioxide; N₂O: Nitrous Oxide; Gt: Giga Tone; CO₂-eq: Carbon Dioxide Equivalent