Here is a great link from The Best Friends Animal Society regarding Pets and Hot Weather.
Pets and hot weather

I have two small Yorkshire Terriers.  They both eat the same food, and yet one of my dogs has stomach issues from time to time.  My vet recommended that I try a probiotic and that has really helped my little guy.  Here is an article I just came across talking about probiotics and pets.

Probiotics and Pets