Are horse timothy cubes safe for guinea pigs?

I buy horse bales of timothy/orchard grass blend of hay or pure timothy for my pigs at Southern States -- the 2nd and 3rd cuts which are typically fed to horses are ideal for pigs too since they aren't as coarse as 1st cuts. No need to waste money spending $8~10/pound of Timothy hay at a pet store when you can get a bale for the same price or less!