Won't need dairy nuts or any kind of concentrate if kept as pets, as others have said. Grass nuts are given as treats by some people, though I have not used them. Carrots are also good, but they may not eat them if they don't know what they are
mine also love bananas as treats (or when heavily pregnant), incl the peel.
But they will need good hay more or less ad lib, and in summer they will love browsings//fresh cut branches from most native deciduous trees - like willow, hazel, some beech, ash, etc etc. Don't feed any evergreens with the exception of ivy leaves (no berries though, just cut them off), they are a good winter treat in moderation.
wrt to sugar beet shreds, they ar sometimes thought to cause bladder stones in males, esp castrated ones. As you don't know if the castration was done properly (with that I mean the urea tube wasn't pinched in anyway, making it narrower) I would just not feed them - there is enough other stuff out there.