The rumen contains bacteria and protozoa that break down plant material using a process called fermentation. This process enables the cow to gain nutrition from a plant-based diet. A byproduct of fermentation is methane – a greenhouse gas. This gas is burped out by cows through their mouths. Cows produce 250–500 litres of methane a day, so research into reducing how much methane cows burp is important.
Image: Cows eating from a ‘green machine’ that measures methane output. © DairyNZ and The University of Waikato Te Whare Wānanga o Waikato.