Can Guinea Pigs Have Hay?

Yes. They need an unlimited supply of timothy hay all the time and alfalfa hay if they are pregnant.
indeed guinea's do eat hay which they like most as straw can sometimes poke in there eyes whilst they are eating and hurt them. guinea pigs are vegetarian though so they only eat veggies. they also LOVE the summer time go out side and snip a little bit of grass off (not to much as can cause wind...) they like this. i give my piggies (all 24 of them as i live in a guinea pig foster centre) hay and saw dust in their cages. they will eat the hay and play in the saw dust.