First, I am glad that he has none of those more concerning signs and that Oscar isn't the kind of dog to eat harmful items. As well, its good the stools are black nor the vomit as I described, as those can be signs of stomach ulcers in dogs. With those aside, as I am sure you can appreciate, that the nausea that caused him to vomit will be the same nausea that is putting him off his food. Often dogs will refuse to eat for worry of vomiting more. Therefore, we do need to focus on that underlying issue for him. Now just to note, common causes for what we are seeing here would be a brewing bacterial or viral gastroenteritis, pancreatitis, parasites/protozoa infections, and general dietary indiscretions. As well, at his age, we do have to be aware that we can also see these signs associated with metabolic or organ dysfunction (ie kidney or liver disease), IBD, and even cancer.
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 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 try 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. 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. As long as improvement is being seen, I usually advise continuing this until the signs are settled, and then weaning him slowly back to his normal diet.
Since dehydration is a risk, we need to keep an eye on his hydration. To check this, there are a few things you can test. Further to checking for gum moisture, do 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 for dehydration, you can find a good video HERE (http://www.ehow.com/video_12232503_dog-dehydrated.html). If you do see these signs already, then that would be our cue to have him checked by his vet before this can make him feel poorly.
Overall, a wide range of agents could trigger the nausea induced appetite loss we are seeing with Oscar. 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. They can assess his hydration, test a blood sample to make sure his organs are working as they should, 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, appetite stimulants, +/- antibiotics to settle this and get him back feeling like himself.
Please take care,
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