Now in regard to your question, we can see rapid deterioration and weight loss in dogs that are anorexic secondary to nausea. So, it is not surprising to hear that he is already showing weight loss and a lack of energy with what is essentially self-starvation to avoid further vomiting.
In regards ***** ***** for this at his age, we do have a range to consider. Common ones include bacterial or viral gastroenteritis, pancreatitis, parasites/protozoa infections, general dietary indiscretions, and ingestion of harmful items (ie toxins, plants, non-edible items). As well, since Taki is older, we also have to be wary of organ troubles (ie liver, kidney), cancer, or metabolic diseases as these too can cause secondary anorexia.
With this all in mind, 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)
* 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 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.
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, 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. And I would note that while its tempting to syringe feed dogs off their food, we cannot do so if he is vomiting.
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).
Overall, a wide range of agents could trigger the anorexia and nausea we are seeing with Taki. Therefore, in his case, we’d want to start supportive care to settle his stomach. If he cannot keep that or any water down(offer it in sips or as ice cubes since over drinking can trigger vomiting too), 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. They can also check a general blood sample to ensure his organs are working as they should. Depending on their findings, his vet can treat him with injectable anti-vomiting medication +/- antibiotics to settle his stomach, get him back feeling like himself, and advise you on any other underlying concerns that may need to be addressed for him.
All the best,
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