Can they

Question
Can hay stop guinea pig constipation or can only grass do that?

Answer
I don't know Jasmine as I don't do guinea pigs. You can get answers for that here:

http://www.allexperts.com/el/Guinea-Pigs/

If not I suggest you ask one of the vets in here that might see guinea pigs or contact your local pet store. Most of them are pretty good about knowing what to do for guineas.

Since I don't work with guinea pigs I don't know that much about them. I would think that either grass or hay would work however, since both are roughage. I have never heard of a constipated guinea pig!