Adult rabbits should have unlimited access (24/7) to fresh GRASS hay. Timothy is the most commonly-available grass hay and it's very healthy for rabbits, but other grass hays are also good, like brome, orchard grass, meadow grass, etc. Oat hay is common and it is recommended but many sources say it should be considered a treat hay, not a regular hay, because it's high in carbohydrates/fat.
Alfalfa is a legume hay, not a grass hay, and it isn't healthy for adult rabbits because it's too high in protein and fat. If you have alfalfa hay around and your adult rabbit likes it, a little bit now and again is probably okay as a treat; otherwise,
alfalfa is a great hay for juvenile rabbits because they're still growing and need the extra protein. (Juvenile rabbits are those under 7 months; from 7 to 12 months, rabbits should slowly transition from a juvenile to an adult diet.)
Hay should always be fresh: - It should look greenish and not too yellowy (some varieties of hay are more green than others; timothy, for example, should really be rather green)
- It should smell sweet
- It should be not too dusty
- It should not be filled with straw (straw is NOT hay)
- It should be dry and free from mould and rot
If you buy hay in bales, break it up before giving it to the bunny: it's not at all uncommon to find dead rodents and insects (even living scorpions!) inside hay bales.If your rabbits aren't eating much hay on their own, you must find a way to encourage them to eat more: rabbits need the high fibre of hay to keep their teeth worn down and to keep their digestive system healthy. If a rabbit doesn't eat enough fibre, all kinds of health problems can result. Hay has the added benefit of keeping your rabbit occupied so that she's less likely to go looking for trouble.