There has been much speculation as to why domestic cats eat grass. The best answer comes from Dr Desmond Morris. The other six don’t stand up to the facts. They eat grass occasionally and in quite small quantities. They ingest the juices from the grass. There something in the juice which they want. Desmond Morris has decided that it is the folic acid inside the grass which is a vitamin and which is vital to cats. It plays a role in the production of haemoglobin which carries oxygen around the blood.
Other reasons suggested are: that grass acts as a laxative to help remove herbals, makes the cat vomit to vomit up hairballs or something toxic, it helps to alleviate the discomfort of a sore throat, helps to relieve stomach irritation and finally it acts as roughage to their diet. All of these don’t really stack up and I favour Dr Desmond Morris’s answer.
