First, I am glad to hear that Donkey likely hasn't eaten something that could be causing GI trauma or a blockage. If that had been a concern, then we'd want him seen urgently. That aside, we do have a few concerns for Donkey's upper and lower GI upset. Common causes we need to consider include bacterial or viral GI infections, parasites/protozoa infections, and dietary indiscretion.
With this all in mind, it does sound like he has a primary lower GI bug that may not be irritating the colon (causing the red material and nausea/vomiting) but if he cannot keep any water down we need to tread with great care. To start, as long as he hasn’t just vomited (since otherwise we’d need to rest his stomach for a few hours first), then you can consider treating him with an antacid. 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 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. And I would note that 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.
If he can keep that down and steadies, then we can try him with small meals (spoonful to start) of a light/easily digestible diet. Examples you can use are boiled chicken, boiled white fish, scrambled eggs, or meat baby food (as long as its free from garlic/onion). There are also OTC vet diets that can be used (ie Hill’s I/D or Royal Canin’s sensitivity) too. Again offer this as small meals with breaks of 20-30 minutes.The aim of these diets is that they will be better tolerated/absorbed by the compromised gut which should reduce upset and his diarrhea volume.
Since dehydration is a risk for such a young cat, we need to keep an eye on his hydration. To check this and ensure he’s not becoming dehydrated, there are a few things 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 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 him seen before this becomes an additional issue for him (especially as it is often dehydration that makes them feel unwell).
Finally, since he hasn't had severely bloody 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 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 using Pepto Bismol or anything with aspirin/salicylic acid as these are not cat friendly). Otherwise, Propectalin, Canikur, 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 his upset GI.
Overall, there are a wide range of agents could trigger this GI upset we are seeing. Therefore, we’d want to start supportive care to settle his stomach. If he cannot keep that down, appears dehydrated already, or doesn’t respond to the above within 8-12 hours (since he is so young and at risk of dehydration); then we'd want to get his vet involved. They can assess his hydration, rule out fever, make sure there is nothing in his stomach that shouldn't be there or any sinister viruses present. Depending on their findings, his vet can treat him with injectable anti-vomiting medication +/- antibiotics to settle his stomach, and get him back feeling like himself.
All the best,
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