Now what I had typed before was that if we have 2 cats with similar signs, then infectious agents and shared exposures would be most likely here. With her long term use of steroids, its low frequency dosing and lack of black stools; the Prednisone is likely innocent here. That said, it plus her aged immune system may be why this is taking a bigger toll on Nadia and causing her to have these colitis type signs (the mucus/blood) as well. Just to note, as long as the grass isn't treated with any chemicals, its likely innocent too.
Now I appreciate she isn't keen for vet visits, but I do want to note that we need to tread with care. Especially if she isn't able to eat. This is because Nadia's signs are suggestive of nausea still being an issue. Cats with nausea often go off food to avoid vomiting. While this is logical, it isn't a good idea for them as they can end up with secondary fatty liver syndrome if they do so for too long. Therefore, we need to be proactive and get her settled and eating for us as soon as possible.
With this in mind, I would note that you can try her with an antacid just now. This is good for settling stomachs but also is good to use before steroid treatments (to offset its GI upset effects). Common OTC pet safe options would be: 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 food to allow absorption. Of course, do double check with your vet if she has a known health issues or is on any medications you haven't mentioned.
Once that has had time to absorb and she is steadier on her stomach, you can re-offer the foods you have. Or you can try her with boiled white fish, scrambled eggs, or meat baby food (as long as its garlic/onion free). There are also OTC vet diets that can be used (ie Hill’s I/D or Royal Canin’s sensitivity) too. The aim of these diets is that they will be better tolerated/absorbed by the compromised gut. Therefore, it should get more nutrients in and result in less GI upset and diarrhea. As long as improvement is being seen, I usually advise continuing this until the signs are settled, and then weaning her slowly back to her normal diet.
Since dehydration is a risk here, we need to keep an eye on her hydration. To check that she isn't dehydrated, there are a few things you can test. Further to checking for gum moisture, do make sure she doesn’t have sunken eyes and that she doesn’t have a "skin tent" when you lift the skin. To see how to check these parameters for dehydration, you can find a good video HERE (http://www.ehow.com/video_12232503_dog-dehydrated.html). If you are seeing any signs of dehydration already, then that would be our cue to have her seen before this becomes an additional issue for her (especially as it is often dehydration that makes them feel unwell).
Finally, since her colitis signs are likely secondary to the loose stool, you can consider trying a pet safe anti-diarrheal. As I am sure you appreciate, these would not be a cure for infectious issues; 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, 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 but do avoid any with aspirin/salicylic acid (as these are not cat friendly and will interact with steroids). Otherwise, Propectalin, Fast Balance, and Protexin Pro-Fiber (all 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 as a short-term means of soothing her upset GI.
Overall, there are a wide range of agents could trigger this GI upset we are seeing but with both cats showing signs this is most likely infectious (so bacterial or viral). Therefore, we’d want to start supportive care to settle her stomach. If she cannot keep that or water down at any point, appears dehydrated already, or doesn’t respond to the above within 12-24 hours (since she is a delicate older lass); then we'd want to get her mobile vet involved. They can assess her hydration, rule out fever, make sure there is nothing in her stomach that shouldn't be there or any sinister viruses present. Depending on their findings, her vet can treat her with injectable anti-vomiting medication +/- antibiotics to settle her stomach and get Nadia back feeling like herself.
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