Hay is messy and annoying but at the same time you have to embrace it as it's so vital to good rabbit & guinea pig care. A piggy and rabbits diet should be 80-90% hay based - it should be unlimited and coming out of your ears. This is certainly the case in my flat.
Hay is a super food - crucial for digestion & good dental health. It's the most important thing in their diet. People often focus on vegetables, what different kinds they can eat, how often they can eat it and so on. In reality making sure your rabbit/piggy eats hay is the most important thing. Of course rabbits and piggies need veg (guinea pigs can't make their own Vitamin C so it's very important for them) but researching if they can eat a mango isn't very important in the grand scheme of things!
It's a similar story with dried food. People are fixated on filling up the bowl every morning and evening with the stuff seeing it as the main part of their diet. In reality pigs/rabbits often gorge on this high sugar diet and then don't eat the hay and veg they should leading, predictably to dental issues later in life.
Normal rabbit teeth
Rabbit with severe dental problems
Hay is a bit of a mindfield. I buy a hay from a farm but you can get allsorts of varying prices. Meadow Hay, Botantical Hay, Green Oat Hay, Wheat & Barley hay, the list goes on.... If you want to splash the cash have a looky at what you can buy online. If you have lots of small mouths to feed like me, maybe stick to the bale! No hay is bad hay (alfalfa is high in calcium so only suitable as a treat for adult pigs.)
You can get hay in cake stylee too for the fussy eater...
So message of the day, step away from the dried food, don't worry that your pet doesn't eat a myriad of veg and fruit - pile on that hay & stick to a few veggie staples!
Here's some Mouse pictures too for you.....