A rabbit's natural diet consists mainly of grass, and in the absence of an unlimited supply of grass the next best thing to form the main part of a rabbit's diet is hay. Hay is grass that has been cut and left on the field to dry with regular turning to ensure it dries quickly to prevent any rotting.
A rabbit should have constant access to grass or hay as the fibre contained is vital to their digestion. A rabbit will spend most of its day eating grass or hay so it also helps to keep them occupied. Any grass a rabbit has access to should be free from soiling by other animals and chemical treatments. Grass clippings should never be fed to a rabbit as they can cause stomach upsets.
Any hay given to rabbits should be dry, clean and free from dust and mould.
There are different types of hay available, some more suitable than others for rabbits.
Timothy Hay
Timothy grass is a perennial grass native to most of Europe with leaves that are up to ½" across. It is relatively high in fibre and Timothy hay is a good quality hay suitable to feed to all rabbits as their main diet.
Oat Hay
Oat Hay is made from the oat plant and harvested before the oat develops into a seed. Oat hay is high in fibre and low in protein and suitable for feeding to all rabbits as their main diet.
Alfalfa Hay
Alfalfa is perennial legume and Alfalfa hay has a high mineral and vitamin content and can be high in protein. It can be beneficial to young growing rabbits and also pregnant and nursing mothers. However, alfalfa hay is considered too high in calcium and protein for continued use throughout adulthood although can be given as an occasional treat.