English Translation
Cattle feed on grass.
Why is there a と in this sentence?
The “と” particle in this sentence is used to indicate a natural condition or habit. It’s similar to “as” in English. The sentence “牛は草を常食とする” translates to “Cows take grass as their regular food.”
The “と” here can be interpreted as indicating “as” or “in the capacity of”. So in this case, the grass is seen “as” the regular food of cows.