Potential of condensed tannins for the reduction of emissions of enteric methane and their effect on ruminant productivity

Methane (CH4) gas is a by-product of anaerobic fermentation of carbohydrates in the rumen of ruminant species. Agriculture contributes with 47% of anthropogenic emissions of CH4, being the ruminants responsible for 39% of enteric emissions of CH4. This greenhouse gas (GHG) has twenty-five times higher global warming potential than CO2 and represents a loss of up to 12% of the gross energy consumed by ruminants. The aim of this review is to describe the mechanisms of action of condensed tannins contained in foliage of trees and shrubs, and their effect on rumen microbes, as well as their potential for mitigation of CH4 emissions. The findings suggest that condensed tannins reduce protozoa population up to 79% and along with this, rumen methanogens are decreased by up to 33%. Condensed tannins bounded to proteins and polysaccharides of the ration form complexes which reduce digestibility of dry and organic matter and production of metabolic used by methanogens to reduce CO2 to CH4 In vitro studies suggest that condensed tannins may reduce rumen CH4 up to 63% in vitro and up to 58% in vivo. Additionally, incorporation of condensed tannins in the ration of ruminants might increase weight gain by 26%, maybe due to the increase in the flow of protein of low rumen degradability to the small intestine or to the reduction of energy losses as CH4 in the rumen. It is concluded that incorporation of condensed tannins in the ration of ruminants at 3-6% of dry matter concentrations can reduce CH4 emissions as well as to improve weight gain and milk yield of productive animals.