hay and grain that the animal consumes, breaking it
down into simpler substances that the animal is able to
absorb. Cellulose is the tough insoluble fibre that makes
up the cell walls of plants; it gives the plant structure.
Animals can’t break down cellulose directly as they don’t
produce the neccessary digestive enzymes.
The methanogens, a group of archaea that live in the
rumen, specialise in breaking down the animal’s food
into the gas methane. The ruminant then belches this gas
out at both ends of its digestive system. Methane is
a very powerful greenhouse gas because it traps about
20 times as much heat as the same volume of carbon
dioxide. As a result it warms the planet up to 20 times
more than carbon dioxide. Around 20% of global
methane production is from farm animals.