I have 2 guinea pigs in a 4x5 cage and I have seen a mouse running around my room. I’m unsure if it will get into their cage. Will it harm my pigs? They are munching on hay right now and I can’t find the mouse!
Depending on the size of the grid or bars, it could potentially get into their cage in search of their food if the cage is at ground level. This is something you don't want to have happen because wild mice can spread disease and can bite or otherwise injure a guinea pig (they're small but a lot more agile and naturally aggressive than a guinea pig.) If possible I would try to keep the cage off floor level and put down some sort of trap for the mouse. Also make sure that any pet food is in a sealed container (like Tupperware, not a bag that can easily be gnawed through.) Hope this helps a bit!