Potential for Reducing On-Farm Greenhouse Gas and Ammonia Emissions from Dairy Cows with Prolonged Dietary Tannin Additions

Dairy cows are responsible for significant emissions of enteric methane (CH4) and produce nitrous oxide (N2O) and ammonia (NH3) gas from manure. As an abatement strategy, we explored the effects of long-term condensed tannin (Quebracho and chestnut extracts) addition to dairy cow diets. Previous studies have demonstrated that tannins in cow diets reduce methane and ammonia efflux, but none have done so over a >1-month time period. A modified stanchion barn equipped with gas analysis instrumentation measured CH4, N2O, and NH3 fluxes into and from the barn, at the onset of the experiment, and 45 and 90 days after feeding groups of lactating dairy cows a control diet or two levels of tannin extract at 0.45 and 1.8 % of dietary dry matter. Few statistical differences among treatments were observed, likely a consequence of high variability and low sample size necessary for conducting a study of this duration. However, on a per-cow basis, low and high tannin diets lowered CH4 emissions by 56 g cow(-1) day(-1) and by 48 g cow day(-1), respectively. Diet tannin additions lowered CH4 (33 %), NH3 (23 %), and N2O (70%) per unit milk corrected emissions in the high tannin treatment compared to the control at the end of the experiment, without significant loss in milk production. These results suggest that relatively low concentrations of diet tannin additions can reduce ruminant CH4 and gaseous N emissions from manure. The tannin effect observed after 90 days is a starting point for considering tannin additions as a potential long-term strategy for improving the environmental footprint of milk production.