Question

ruminants like cows, buffaloes etc. eat grass and raw green leafy vegetables and digest it but humans cannot do so. give reason

Answer 1

Because animals have a well developed cellulose digesting power.The raw green leafy vegetables contain a lot of fibres and when they are consumed by the animals the fibre gets converted into cellulose and they use to build their cell wall whereas in humans its not well developed but still we have Appendix as a cellulose digesting organ. Fibre causing no harm gets digested easily in our body.Hope it helps

Answer 2

the food which cows eat is totally grass which is made up of cellulose they have a four chambered stomach in which there is bacteria which helps to break down cellulose to some extent. we lack the bacteia of breaking cellulose 
so we cannot digest the food like ruminants