I usually contact Oxbow for these things. Their customer service is great in dictating ingredients and you can request to consult their vet about the implications of particular ingredients. In my correspondences, they never push their products or anything.

EDIT: I add apple cider vinegar with the mother in Wick’s water since I’ve had him. The bacteria of the mother helps regulate pH levels. I’ve never seen Wick without it, so if anything, it helps keep his coat shiny and soft, eliminates urine smell, and encourages him to drink more.  Medically, he’s never had digestive issues so this could be why.

I use digestive supplements for Bombur. He has a super sensitive tummy, and has been prone to GI issues. I give him a Trader Joe’s papaya pineapple digestive enzyme everyday, usually when he eats his greens. It’s really helped him a lot, especially now that he’s moulting.

I give Bam probiotic pellets, just a few, every day because he’s prone to sticky poop.

I think there’s a lot of individual variation when it comes to tolerance of pellet ingredients. According to my rabbit-savvy vet, fiber content is the most important aspect of rabbit food. 20% is the lowest acceptable amount of fiber. Oxbow essentials has 25.

When I was caring for a bunny with serious tummy troubles, I tried the Oxbow digestive support supplements. He loved them, but I have no idea if they helped or not… but I did like them as a metric to make sure he was feeling OK, because they were a treat that I knew wouldn’t upset his tummy more. I would also try to supplement him with lots of wild forage (at the advice of folks here), which is higher fiber than the veggies we typically feed. Dandelion, plantain, and sow thistles were big hits…. can’t wait for them to be in season again! It’s bone dry here in CA (and also on fire near me… ugh)…. so hoping we get some rain soon.

With this tummy issue bun (Pippen), I was reluctant to take away pellets because he also was very underweight, so we were basically trying to get him to eat as much of everything as possible. We did try taking away each element of the diet in turn to see if there was a trigger, and couldn’t identify any dietary source of his troubles.

I did give Moose Bene-bac paste while he was on penicillin shots, and I think they helped his poops a bit, as they were getting smaller and darker from the penicillin (but I think that was also due to reduced hay consumption because his mouth was hurting him).