Why Do Some Animals Poo In Pellets?

My kids would like to know why sheep poo and cow poo is different. Both cows and sheep eat grass. But cows do 'pats' and sheep do 'pellets'. Why is this?

Response:

Name: Frank, Sevenoaks

Qualification: Went to agricultural college

Answer: Cows have four stomachs so they process the grass a lot more effectively than sheep do. As the grass goes through each section of their stomach it gets more and more absorbed. Just soft cow pat is left.

Name: Omar, Gravesend

Qualification: Has a degree in biology

Answer: It is about moisture retention and evolution. Cows do wet pats rather than pellets because of how they have evolved. Cows evolved on lowlands and forests where there is plenty of water. Sheep have evolved in mountains where there is a lot less moisture. So when sheep excrete their droppings, they have taken the moisture out of their food, and so they have hard pellets.