I’m always a bit skeptical of home remedy type things, because you never really know if the bun just naturally fought off the infection on their own. I can’t really imagine apple cider vinegar doing anything…
I’m not familiar with GSE, but I did find a published paper on it having a benefit in wound healing in rabbits. If the echinacea is formulated for rabbits then I imagine it would be safe to use as directed, but I would definitely check with your vet as certain herbs can interfere with certain medications.
That said, I do like the herbal blends from Floppers Garden (if you can get them), as they are formulated for rabbits and provide additional variety in their diet. I’ve used the “old bones” mix for my senior buns and I felt they were more comfortable when they got it.
I think the best things for bun immune system would be adding variety in the diet, in the form of different hay types, greens, and herbs. Natural forage (weeds) can be very healthy for bunnies as they are more nutrient dense than the veggies we grow for our own consumption.
I’m also a fan of changing only one thing at a time. Since you just made the decision to change her treatment regimen and are getting the mold situation cleaned up, I would wait a bit to see if you see some improvement with those changes before trying anything else.
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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.