Powell began investigating tannins in animal feed 20 years ago in West African communities where he lived and worked. Tannin-rich shrubs were grown as windbreaks to reduce soil erosion and to feed livestock. Tannins also are a key part of the diets of cattle, sheep and goats in tropical areas where vegetation tends to be naturally higher in the astringent plant chemicals. However, tannins have attracted relatively little attention elsewhere, Powell said.

He hopes the addition of tannins to animal feed will become much more widespread in light of the findings about their potential for curbing ammonia emissions. The tannin extracts used in the studies are already approved for animal feed and would cost only a few cents a day, he said. Tannins are perhaps best known for their use in tanning leather, and the quebracho and chestnut trees are sources for both leather tanning and cattle feed. Powell said that it may be possible to produce synthetic tannins at a lower cost.

Next on Powell’s agenda is research to determine whether tannins also can reduce emissions of methane gas — a potent greenhouse gas involved in global warming — from cattle production. About 25 percent of methane emissions in the United States are from enteric fermentation (mostly belches) of domestic cattle.

(This research was presented at a meeting of the American Chemical Society.)