Hi Bessie and welcome to the forum!! Fiber is a good idea, something like benefiber that you can add to anything as it's tasteless.
I made my doctor test for everything that can be transmitted by animals (I have dogs, horses and filthy chickens) : coccidia, gihardia (sp?) leptospirosis, c-diff and something else that I can't remember.
Probiotics are also a good addition, good bacteria for the gut. If one of the dogs gets the runs they get a course of flagyll.
I have one dog diagnosed with SIBO (small intestinal bacterial overgrowth) it is thought to be immune mediated. I have often wondered if humans can have that also.