Q. Is there any problem with feeding a guinea pig, (store bought) hay on Pesach?

A. Horav Shlomo Miller’s Shlit’a opinion is that If it is grass hay, there should not be any problem even when bought on Pesach. Legumes hay, should better be acquired before the Yom Tov begins, shaken and inspected for the unlikely case that there is still some grains of cereals left.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a