Asked by: Graham Barnes, Sussex
Cows are ruminants. This means that their food is chewed twice: once when they graze, and then a second time when partially digested grass (cud) is passed back up to the mouth for another going-over. This, plus the four-chambered arrangement of their stomachs, makes ruminant digestion about 70 per cent more efficient than other herbivores, such as horses. So the poop that finally emerges is more completely broken down and has none of the leftover plant fibres that give horse droppings their structure. Cows fed on silage, which is already partly fermented, have even runnier manure.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.
