FIRST, i would like to say sorry for all these troubles and sorry to hear about your grandpa. I know this is frustrating not knowing for sure what is making snickers sick!
One thing to consider is, you have no idea how long he was out on the streets and what he picked up.
Did they xray his belly to make sure he didnt have a foreign object in his belly/intestines?
I would remove him from
ALL grains. If he does Have IBS, the last thing he needs in an inflamatory causing food!
The fevers worry me. his body is raising its temp in effort to fight off something.
There is definately something they are missing..and hope you find out soon
Good luck. Bella and Piper send Snickers many healing and sweet kisses!