Now I am glad to hear that his belly is comfortable but if you aren't sure he can pass urine, do monitor for that as that is a male cat emergency when they cannot do so. Otherwise, hopefully those gums are pink (as you answered no instead of a color) else if they were pale we'd again have another urgent issue. With that aside, given his signs of appetite loss, we do have a few worries. Especially if he is drinking a lot more. This is because while gut infections, dental disease, and pancreatitis are concerns for appetite loss, the drinking ring alarm bells of kidney or liver disease, diabetes, hyperthyroidism, and some cancers (that increase blood calcium levels).
With this all in mind, we can try some home supportive care. To start, to try to counter any nausea he may have, we can try 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.
Afterwards, we can try him with small meals of a light diet like boiled chicken, boiled white fish, 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. If your wee one cannot be tempted, we can offer or syringe feed watered down canned food, Hill's A/D, Royal Canin Recovery, or Clinicare Canine/Feline Liquid Diet. All of these are critical care diets that are calorically dense, so a little goes a long way nutrition-wise. There are also gel/pastes (ie Nutrical, GNC) that we can use here.
Finally, as dehydration is a risk we need to keep an eye on his hydration. To check that, there are a few things you can look for. Besides gum moisture, make sure his eyes aren't sunken and that he doesn’t have a "skin tent" when you lift the skin. To see how to check those dehydration signs, here is a good video ( http://www.ehow.com/video_12232503_dog-dehydrated.html ) to look at. If you do see any signs of dehydration already, that's our cue to have him seen before this becomes an additional issue (especially as it is often dehydration that makes them feel unwell).
Overall, his signs do raise some concerns especially with the increased thirst on top. So, we’d want to start the above supportive care now. If he doesn’t respond to the above within 12-24 hours (or if you think he cannot pass urine then sooner); then we'd want to get his vet involved. They can assess him with a view to starting appetite stimulants, injectable anti-nausea medication +/- antibiotics to get him eating properly before he fades away on us.
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