I am glad to see that he was covered for worms; though I am a bit surprised he was vaccinated while having diarrhea. The reason that is a bit of a concern is because while diet related diarrhea isn't overly worrisome, we can also see this with brewing gut infections (ie viruses, bacteria, protozoa) and it won't help to have his immune system distracted if he is trying to fight one of those off. Therefore, I will outline some supportive care for you to start now but if this lingers over 24-48 hours we may need to take a fresh stool sample to his vet for testing to make sure nothing infectious has been missed.
Now to start, instead of canned or dry food, you can try an easily digestible diet like cooked white rice with boiled chicken, boiled white fish, cottage cheese, scrambled eggs, 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. 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 signs are settled, and then weaning slowly back to your normal diet.
Furthermore, to reduce the diarrhea and bind it, you can consider trying a pet safe anti-diarrheal. As I am sure you appreciate, these would not be a cure for infectious issues; but it can still be of benefit. It will reduce diarrhea load, allow the body to absorb more water/nutrients, and soothe the upset gut. In regards ***** ***** options, the one we most commonly use is Kaolin/Kaopectate (More Info/Dose @ http://www.petplace.com/article/drug-library/library/over-the-counter/kaolin-and-pectin-kapectolin-k-p)). This is available OTC at most pharmacies. Otherwise, Propectalin, Canikur, Fast Balance, and Protexin Pro-Fiber (all OTC at vets, pet stores, and even Amazon) would be another option. All will slow diarrhea and those last ones have the added bonus of providing support to the delicate good GI bacteria. So, these can be used as a short-term means of soothing his upset GI.
Finally, as dehydration is a risk in these situations, do 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 here. Therefore, we’d want to start the above supportive care now. But if we cannot get him settled with the above then we'd want the local vet to reassess and test a stool sample looking for those other concerns.
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