Now I am glad to hear that he is comfortable, but if you can even just lift his lip (as opposed to opening his mouth) or roll his lower eyelid down to check that his mucous membranes are pink (since pale/white is an urgent sign) that would be ideal. That aside, if you weaned him over to the new diet, then we'd hope that isn't to blame but if the switch just started so recently we do have to be wary of it being out culprit.
Therefore, we'd want to start supportive care for Piper in case that is the cause. Of course, we'd also have to keep issues like bacterial or viral gastroenteritis, pancreatitis, parasites/protozoa infections, general dietary indiscretions, and ingestion of harmful items (ie toxins, plants, non-edible items) in the back of our mind if we cannot get him settled.
With this all in mind, as long as he can keep water down, we can try some home supportive care to try to settle his stomach. To start, if he hasn’t just vomited (since otherwise we’d need to rest the stomach for a few hours first), you can consider treating with an OTC pet safe antacid [ie Pepcid (More Info/Dose @http://www.petplace.com/article/drug-library/library/over-the-counter/famotidine-pepcid), 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 double check with your vet if he has a known health issues or is on any medications you haven't mentioned. Also if you give this and he cannot keep it down due to nausea that is usually a red flag that we need to bypass his mouth with injectable anti-vomiting medication from his vet.
Once he is more settled, you can plan to try small meals of a light/easily digestible diet. Examples you can use are boiled chicken, boiled white fish, or scrambled eggs, or meat baby food (garlic/onion free only) There are also OTC vet diets (ie Hill’s I/D or Royal Canin’s sensitivity) that can be used 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 less diarrhea. Fiber (ie canned pumpkin, 0.25 tsp metamucil mixed into canned food) can also be given +/- OTC feline probiotics (ie Benebac, Fortiflora) can also be used as the former will firm the stools quicker and the latter will support the gut's microflora. As long as improvement is being seen, I usually advise continuing this until the signs are settled, and then weaning slowly back to what you were feeding before. And once he is totally settled, you can decide if you want to try the new diet again.
Since dehydration is a risk with his having both vomiting and diarrhea, we need to keep an eye on his hydration. To check this and make sure dehydration isn’t an issue, there are a few parameters you can test. Further to checking for gum moisture, you will want to make sure his eyes are not looking sunken and that he doesn’t have a "skin tent" when you lift the skin. To see how to check these, you can find a good video HERE (http://www.ehow.com/video_12232503_dog-dehydrated.html). If you do see any of these signs already, then that would be our cue to have him seen before this becomes an additional issue (especially since its often dehydration that makes them feel unwell).
Finally, as long as there is no blood in those stools, 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 OTC Kaolin/Kaopectate (More Info/Dose @ http://www.petplace.com/article/drug-library/library/over-the-counter/kaolin-and-pectin-kapectolin-k-p)). Avoid Pepto Bismol or Imodium 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 as a short-term means of soothing his upset GI.
Overall, a wide range of agents could trigger the signs we are seeing but the diet change is one concern here for Piper's signs. And since that usually respond to supportive care, we can try the above for him. Of course, if he cannot keep that or water down, appears dehydrated already, or doesn’t respond to the above within 12-24 hours; then we'd want to get his vet involved. They can assess his hydration, rule out fever, ensure nothing in his stomach that shouldn't be, or any sinister viruses present. Depending on their findings, his vet can treat with injectable anti-vomiting medication, fluids, +/- antibiotics to settle his stomach and get him back feeling like himself.
Please take care,
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