First, if there is any doubt on the FIV test (which if the vet read the test after the set time then it may have been a false positive), then it would be ideal to have this result confirmed. To do so definitively, you’d want them to send it to the local vet lab for testing. That way were can know if he truly is positive no matter of the in-house test being wrong or if there was an error in their interpretation.
That aside, if Chicken isn’t eating/drinking properly, we’d be quite concerned about an underlying nausea potentially from something he ate or a brewing infection or pancreatitis. In all cases, the lapse in eating/drinking will cause dehydration and a low blood sugar; which could cause weakness and wobbliness. Though I have to note that if his gums are paler then usual, then we do have a risk of anemia (low red blood cell levels) which could also cause these signs. And that would raise concerns of an internal bleed or possible bone marrow issue (which could suggest FIV). So, we want to tread with care.
With this all in mind, as long as he can keep water down, we can try some home supportive care to try to settle any lurking nausea. To start, if 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. Though 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 that has had time to absorb and he is steadier on his stomach, you can consider starting him on a light/easily digestible diet. Examples you can use are cooked white rice with boiled chicken, boiled white fish, or meat baby food (garlic/onion free). Though if he cannot be tempted but isn’t vomiting, then we can start syringe feeding him. To syringe feed, we can water down calorie rich diets (ie Hills A/D, Royal Canin Recovery diet, even canned kitten food) or use a liquid diet (ie Clinicare, Catsure). As well, there are paste supplements (ie Nutrical) that can also be used. And these will all get more in per bite even if we cannot get much in.
Since dehydration is a risk here, 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). And again if he isn’t vomiting, we can syringe feed fluids (ie water, pedialyte) but will want to aim to get 48ml per kilogram of his weight into him daily. Of course, if he vomits when we give this, we’d need to hold off on our syringing.
Overall, I am quite concerned about Chicken as it does sound like we have a few potential issues present. If he is very pale, then anemia is a worry and we’d need to have that checked +/- retest that FIV finding. Otherwise, to tackle any nausea present, we can try the above for him. Though 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, 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 ,fluids, appetite stimulants, +/- antibiotics to settle his stomach, and get him back feeling like himself.
Please take care,
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