I have not head back from you, so I did want to leave my thoughts about Rooney for your return.
Now its good to hear that his bloods were clear, as this does reduce the chance of organ issues or metabolic disease (even if we have to be wary of something arising in (the past month). Still, with those lower on our list of concerns, we do need to consider issues that could trigger nausea --the most common reason for both vomiting and anorexia. Therefore, in Rooney’s case, we’d need to consider a potential bacterial or viral gastroenteritis, pancreatitis, cancer, parasites/protozoa infections, general dietary indiscretions, and ingestion of harmful items (ie toxins, plants, non-edible items). Of course, at his age, we’d hope eating harmful items would be less likely.
Now 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 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), Zantac (More Info/Dose @ http://www.petplace.com/article/drug-library/library/over-the-counter/ranitidine-hcl-zantac), 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, we can then try him with small meals of a light diet. Light diet options we often use are cooked white rice or pasta with boiled chicken, boiled white fish, cottage cheese, or scrambled eggs (made with water and not milk). 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.
Of course, if we soothe that nausea but he refuses to be tempted, we may need to think about syringe feeding to halt the weight loss and get some nutrition/energy back into him. To syringe feed, we can water down calorie rich diets (ie Hills A/D, Royal Canin Recovery diet, even canned puppy food) or use a liquid diet (ie Clinicare, Dogsure). As well, there are paste supplements (ie Nutrical) that can also be used. And these will all get more into her per bite even if we cannot get much in.
Overall, a wide range of agents could trigger the anorexia we are seeing. Therefore, in his case, we’d want to start supportive care to settle his stomach. 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 since he likely cannot afford to be losing weight at his age. 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-nausea medication, appetite stimulants, +/- antibiotics to get him back to eating before he wastes away on us.
All the best,
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