Cattle ruminating on a hillside create a peaceful scene. But their effect on climate change is as grim as their ultimate role in the multi-billion-dollar livestock industry. The belching and flatulence of cattle release a massive quantity of methane, a potent greenhouse gas. Raising livestock accounts for some 37% of global anthropogenic methane emissions. Herbert Steingass, Christian H. Geerkens, and coworkers at the University of Hohenheim, in Germany, report that supplementing cattle feed with citrus could drastically reduce methane production. The group used an in vitro culture from the rumen portion of a cow’s stomach to evaluate apple-, citrus-, and mango-processing by-products as feed supplements. They found that all of the tested materials should be digestible and healthy for cattle to eat. But low-esterified citrus pectin, a carbohydrate extracted from citrus peels, caused a 19% drop in methanogenesis (J. Agric. Food Chem. 2013, DOI: 10.1021/jf401544v). Some mango components also showed promising inhibition of methane production. Although in vivo studies are needed, the team says, these results could lead to benefits for the environment and allow farmers to turn a waste into a valuable commodity.