Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you with your wee one today. I do apologize that your question was not answered before. Different experts come online at various times; I just came online, read about your wee one’s situation, and wanted to help.
Now just like people, when dogs can have diarrhea like this it can be caused by a range of agents. These include bacterial, viral, parasitic (worms but also protozoa like Giardia, Coccidia, Tritrichomonas), toxins (sounding less likely here), nutritional, and general dietary indiscretions type causes.
Now it sounds like you approached the diet change correctly and this is not our culprit. Furthermore, I must note that your mention of Cesar eating all sorts of things he should not (including bacteria filled feces) is very commmon in pups and very commonly our reason for seeing diarrhea in young dogs. So, in this case, his picking up a stomach bug from his misadventures with putting things in his mouth and challenging his naive immune system would be our top suspicions.
Since this has not settled with resting his stomach, we do want to start taking some steps to help him at this stage. First, I agree with your thoughts on a light diet. In regards ***** ***** yo can try cooked white rice with boiled chicken, boiled white fish, scrambled egg, or meat baby food (as long as its free from garlic or onion powder). There are also veterinary prescription diets that can be used in cases of gastroenteritis (ie Hill’s I/D or Royal Canin’s sensitivity). The easily digestible diet will be better tolerated and absorbed by the compromised gut and should get some nutrients in and result in less diarrhea. Also feed this as small frequent meals to further decrease the volume of diarrhea he is producing. As long as improvement is being seen, I usually advise that the diet be continued until the diarrhea is settled, and that they are then slowly weaned back to their normal diet over a week.Now since it has been a few days, I do want to note that diarrhea can dehydrate a dog. Therefore, if want to trial home treatment with him then do keep an eye on his drinking and hydration. To check his hydration status to make sure they are not becoming dehydrated there are a few things we can test. One is whether the eyes appear sunken, if the gums are tacky instead of wet/moist, and whether he has a "skin tent" when you lift the skin. To see how to check these parameters for dehydration, you can find a wee video on this HERE. If you are seeing any signs of dehydration already, then you do want to have him seen by the vet before makes him feel poorly. (since it is often the dehydration that starts to tap their energy level and actually makes them feel ill)
If you were concerned that he was becoming dehydrated, you can try and encourage him to drink but offering fresh water or even low-sodium chicken broth. If he isn’t amenable to these, you can syringe feed pedialyte. Pedialyte is nice (though aim for a flavorless one) because it will get some of those lost electrolytes back into him as well. A typical maintenance rate for hydration in an animal is 48mls per kilogram of weight a day. If you do give syringe pedialyte, this should obviously be divided up into multiple offerings through the day rather then all at once. This value will give you the total he needs for the day and is a good starting point to give you an idea of a dog's daily requirement. (we aren’t calculating losses, so you can add an equivalent volume to match how much diarrhea is being producing). If he vomit when you have given pedialyte, then therapy should be discontinued (since we don’t want vomiting because of our intervention).
Further to this, you can consider trying him today on a dog safe anti-diarrheals. As I am sure you appreciate, these would not be a cure if his diarrhea is being caused by an infectious agent (ie bacteria will require antibiotics, parasites or protozoa will require anti-parasitic treatment, etc). Still it can slow the diarrhea to aid the body to absorb more water/nutrients then it would have if the diarrhea were unchecked. Furthermore, these treatments will coat the GI and could just settle the GI upset. In regards ***** ***** options for your wee one, the one we most commonly use in dogs is Kaolin/Kaopectate (More Info/Dose) or PeptoBismol (More Info/Dose) available from your local pharmacy. Furthermore, Protexin Pro-Fiber (which is available OTC at vet practices; example) would be another option. All will slow diarrhea and the Pro-Fiber has the bonus of providing support to the delicate good bacteria of the GI. So, you can consider trying these as a short term means of trying to soothe his upset GI.
Overall, there can be many triggers for diarrhea of this nature. Since he is young, we do need to be proactive in trying to settle this form him. Therefore, do try the above supportive measures for him. If he has just had a wee dietary indiscretion, these steps should settle this for him. But if you do so but his signs do not settle in then next day or so, then it would be worth following up with his vet. You can even consider having them submit a fresh fecal sample to the lab to be checked for common parasitic, protozoal and bacterial causes of diarrhea. And if this is a bacterial or protozoal complaint, knowing what the causative agent is will help you treat it effectively and clear this abnormal stool to get him back to passing normal feces.
I hope this information is helpful.
If you need any additional information, do not hesitate to ask!
All the best,