Sure, the reason for weight loss should be determined, but nonetheless sometimes a rabbit needs to be fattened up, or needs more calories to not lose weight like some nursing does, no point in watching it wither away. Oats are ok for that, in limited quantities, and it isn't a problem when needed.If your rabbit is losing weight, s/he needs a visit to the rabbit vet to find the cause of the weight loss. It's no good just trying to deal with a symptom. Oats are not recommended at all. High carb food should generally be avoided.
What pellets you feed him, brand or ingredients with % for protein, fibre, calcium.Thanks! He is a little under weight- he is a large baby bun who is still growing. He has all day access to his pellets and hay and gets lfresh greens everyday