“If we add dried seaweed to 2 percent of sheep and cattle feed, we could cut methane emissions by more than 70 percent, scientists have found. With livestock responsible for 44 percent of all human-caused methane – a gas that has 36 times the global warming potential of CO2 – this could cut a huge chunk of the 3.1 gigatonnes these animals release into the atmosphere each year…”
http://www.sciencealert.com/adding-seaweed-to-cattle-feed-could-reduce-methane-production-by-70