I don’t think there are any downsides to daily critical care. It has lots of good nutrition, and is definitely a good supplement for buns that are poorly.
Since you’ve cut out pellets entirely (was this at your vet’s recommendation?), and is on a restricted variety of veggies, you should consult with your vet to make sure he gets all the minerals he needs. Critical care might be the best bet, but your vet might encourage a variety of hays, or some other more nutritious veggies.
In general, veggies that are higher in fiber are better for buns, and often buns with tummy troubles do better with more “natural” forage. An abundance of fiber in the diet helps the gut keep moving, and thus prevents the build up of gas. Dandelion greens, sow thistle, broad and narrow leaf plantain, mint, and fennel are all good for bunnies with sensitive tummys. Mint and fennel especially can help with gas.
Tummy rubs can also really help with gas episodes.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.