Why does a cow have seven stomaches?

Answer 1

This couldn't be more false. Cows do not have anywhere near seven stomachs. In fact, they only have one stomach. That one stomach is divided into three forestomachs (reticulum, rumen and omasum) and one true stomach(abomasum), making that a total of four chambers of that one stomach.

The answer to the "why" part of the question is that it is one part of how a cow is able to consume and digest a 100% forage diet in an efficient manner. The other reason for such efficiencies is the large population of gut microflora in the rumen, which is used to break down cellulose for easier digestibility and give the cow, when they die, a source of protein. A cow needs these chambers to be able to ferment/digest, regurgitate and rechew, ferment/digest again, remove water then digest to break down the coarse plant material they so often consume. Where grass simply passes through a human's digestive system and acts as a source of fibre--better yet a means to mainly clean out the pipes--a cow's digestive system is designed so that as much nutrients can be extracted out of that tough plant material to be used in metabolism, energy, growth, and reproduction.