I) bcz they r designed to eat grass with theirmolar and premolar teeths.
ii) food stuffs which contain a balanced amount of all carbohydrates, fats, proteins etc. yields the maximum amount of energy on complete combustion.
iii) cellulose is not digested in humans as they cannot be easily broken down and in cow this process is possible.
iv) dietary fibers r composed of nonstarch carbohydrate and lignin.
v) vitamins r important for animals even they do not produce energy bcz deficiency of vitamin lead to cause many diseases in animals as well as human beings.