Whoa, puppy milk!?
Guinea pigs are
cavies, not canines, and the nutritional requirements between them are worlds apart! That veterinarian certainly does not sound to know much about guinea pigs if he told you to give it puppy milk. Aren't Guinea Pigs are lactose intolerant?
He should have prescribed you Critical Care.
Puppy milk!? I still can't get over that, that is absolutely absurd.
Please find your animals a better veterinarian, their lives depend on it. And guinea pigs and rabbits should never be housed together.
What a disaster, I want to slap that vet!