A European startup has started selling carbon credits for cattle raised on a feed supplement that reduces the amount of heat-trapping greenhouse gas they release.

Mootral, based in Switzerland and the U.K., says its garlic-and-citrus feed can cut methane emissions from livestock by an average of 30%. Under its offset program, a certified farmer that’s produced milk using Mootral’s supplement can sell credits equal to one ton of carbon dioxide to customers that want to offset their pollution.

Livestock farming accounts for about 15% of global greenhouse gas emissions, largely from cows, sheep and other ruminants that emit methane, a gas that’s more than 80 times more potent than carbon dioxide. Agriculture is making inroads into the $320-million voluntary carbon market, particularly through more environmentally friendly farming, though demand has so far been limited.