Hello, my name is***** and I have over 20 years of experience as a veterinarian. I'm sorry to hear about Olive's loose stools for the past several weeks. I am pleased to hear that these are not slowing her down and she feels well otherwise.
Is she losing any weight?
It will be important to describe what sort of loose stools she has to try and localize the problem. Loose stools with mucous or bright red blood and small amounts frequently point more towards large bowel diarrhea or colitis, whereas just watery stools with no mucous point more toward small bowel disease.
Chronic diarrhea does cause changes in motility of the gut and can lead to reflux and vomiting. It can also lead to bacterial overgrowth in the gut. Probiotics such as Fortiflora, Proviable or Benebac can help replace appropriate bacteria. I understand that you may have tried one probiotic but perhaps a different one will work better.
I assume that she has had stool samples checked to make sure that parasites aren't part of her problem. Sometimes we need to submit these to the laboratory rather than checking them in the clinic to look for more unusual parasites.
Has she had a fecal culture to check for abnormal bacteria such as clostridia?
Is she losing weight?
If she truly doesn't have parasites or abnormal bacteria it is quite possible that she has a food allergy/sensitivity or inflammatory bowel disease and that she needs a low residue, easy to digest food or a hypoallergenic food to be able to properly digest and absorb her food and not have loose stools. I highly recommend a trial of either Hills i/d (which was tried) or Purina Pro Plan Veterinary Diets EN. No treats, table food or flavored medications while she is on her food trial. If he does well she can eat these foods for life as they are balanced.
Cats with food allergies that cause loose stools can benefit from Hills z/d or Purina Veterinary Diets HA.
Cats with inflammatory bowel disease will worsen with stressful situations. There may be times when she will need medications too, such as metronidazole or even steroids too if that is her problem, but I have found that a consistent, easy to digest diet is very helpful for long term control.
We can diagnose inflammatory bowel disease via biopsies, but checking blood levels of folate and cobamalin may point toward primary intestinal disease and what part specifically may be affected. Have those blood tests been done?
There are other possibilities too.
Addison's disease, which is a poorly functioning adrenal gland, can lead to chronic diarrhea and vomiting. These kitties cannot handle stress at all because their adrenal gland doesn't produce cortisone when stressed and their electrolytes can be off too if their adrenal gland isn't controlling that normally either. We see vomiting, diarrhea and sometimes physical collapse in severely affected cats. This is more common in dogs than cats. Testing is an ACTH response test to check adrenal gland function and checking electrolyte levels. Treatment is steroid replacement therapy and electrolyte replacement. This seems less likely with her as she seems well otherwise and Addisonian cats are generally lethargic and otherwise unwell, but I mention it to be complete.
Pancreatic insufficiency is another possibility. These cats have a pancreas that produces a decreased amount of digestive enzymes, and the amount produced can wax and wane in some cases, especially early in the disease process. Testing is by running a blood test called a TLI which checks for digestive enzymes. Treatment is replacement of digestive enzymes at each meal. An easier to digest food would be expected to create less problems with digestion and as such less diarrhea.
Kidney and liver disease can cause diarrhea too, but I would expect her to be sicker in general and these should have been picked up on routine blood tests which sound like they have been done.
In short since this has been a long term problem for Olive then more diagnostics need to be done. They can be as simple as fecal checks and cultures, as well as a complete blood count and biochemistry profile and thyroid levels to assess general health. Or they can be more invasive such as biopsies of her gastrointestinal tract to look for inflammatory bowel disease or infiltrative cancers such as lymphoma. I suspect that your veterinarian is recommending endoscopy to get biopsies, which does make sense if her blood tests have been normal.
In the meantime it may help to offer a bland diet mix of 2/3 boiled, minced, white, skinless chicken and 1/3 boiled, plain, white rice mixed with some low salt chicken broth to make it easy to lap up and swallow as well as increase her fluid intake. If she has mucous in her stool add 1 tablespoon of canned pumpkin (not pie filling, just pumpkin) to each meal to increase fiber, which soothes an irritated colon.
Probiotics such as Fortiflora, Proviable, or Benebac can help replace appropriate bacteria. You can add those to the bland diet mix.
If she does well with that then discuss using a colitis type diet called Purina Pro Plan Veterinary Diets OM.
Please let me know if you have any further questions.