I would listen to your vet, or consult another one, or a specialist. Is there some reason that you think that anonymous strangers on the internet would be able to advise you better than a veterinarian who has examined your dog and knows his history? Doesn’t make sense to me.
Unless, you are just looking for folks to agree with your opinions and encourage you to do something that may have dire consequences for your dog.
Gastroenteritis….that just happens for no reason. NOT.
I am more inclined to follow science based veterinary medicine http://skeptvet.com/Blog/category/nutrition/
https://www.mspca.org/angell_services/choosing-the-right-diet-for-your-pet/
Best of luck.
