First, if she has been on the diet for three months already, we'd expect her current signs to be non-diet related. Its possible that her sensitivities did play a role initially but this length of time would be enough to overcome any previous dietary allergic response.
Now if she has been showing signs for this length of time, we are likely looking at a chronic issue +/- a low grade persistent gut infection that her immune system cannot overcome. And I would note that often the two appear together since systemic issues like metabolic or organ based dysfunction (ie thyroid disease, kidney or liver troubles, low grade pancreatitis, IBD, cancer, etc) can impact the immune system to allow these persisting agents unsteady the gut.
With this in mind and the length of time Putney has had signs, it'd be ideal to have check up +/- a geriatric blood panel tested. If she is due a booster soon, consider moving that appointment up for her. That way we can rule out any sinister lumps and bumps and pinpoint which of the other concerns are present here. Depending on those findings, we can treat her appropriately to reduce her signs and get her settled.
Otherwise, in the meantime I do want to touch on some supportive care options we can try for Putney. To start, if you have not already, do try her with small frequent meals as opposed to 1-2 meals daily. If you are feeding a dry food, it may be ideal to use a canned one (as they expand less in the stomach and can be better tolerated). As well, you could even try a light diet option intended for GI sensitivity in cats like Royal Canin Sensitivity Control or Hill's I/D. Or for the short term, you could trial her on a light diet option like boiled chicken, boiled white fish, scrambled eggs, or meat baby food (as long as its garlic/onion free). Whichever you choose, you can also add a cat specific OTC probiotic like Fortiflora to her food to ensure her GI good bacteria are working as they should to reduce both her signs of upper and lower GI upset.
Furthermore, to counter the underlying nausea that is triggering her vomits, you can try Putney with an antacid. Common pet safe OTC ones we can use include Pepcid (More Info/Dose @http://www.petplace.com/article/drug-library/library/over-the-counter/famotidine-pepcid) or Tagamet (More Info/Dose Here @ http://www.petplace.com/article/drug-library/library/over-the-counter/cimetidine-hcl-tagamet). Whichever you choose, we’d give this 20 minutes before offering food to allow absorption. Of course, do check with her vet before use if she has any known health issues or is on any medications you didn’t mention.
Finally, if she is very runny, you can consider trying a pet safe anti-diarrheal. As I am sure you appreciate, these would not be a cure if the cause were infectious; but it can still be of benefit. It will reduce diarrhea load, allow the body to absorb more water/nutrients, and soothe the upset gut. In regards ***** ***** options for your wee one, the one we most commonly use is Kaolin/Kaopectate (More Info/Dose @ http://www.petplace.com/article/drug-library/library/over-the-counter/kaolin-and-pectin-kapectolin-k-p). This is available OTC at most pharmacies. Do avoid Imodium or Peptobismol with her since those aren't cat friendly. Otherwise, Propectalin, Canikur, Fast Balance, and Protexin Pro-Fiber (which is available OTC at vets, pet stores, and even Amazon) would be another option. All will slow diarrhea and those last ones have the added bonus of providing support to the delicate good GI bacteria. So, these can be used to reduce her diarrhea and settle her gut.
Overall, Putney's signs are more suggestive of a chronic GI upset. Therefore, in her case, the above concerns would be our worries here for her. Therefore, it'd be ideal to have a check and blood test at this point. Otherwise or as well, you can try the above to soothe her stomach and reduce these signs for her. Though depending on her vets exam and bloods, we would be in the best position to know which issue was present here and how best to address it for her for the long term.
Please take care,
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