I am sorry to say your humane society is way off base if they recommend that particular food. SugarLoveRats is right, it is NO good. #1 ingredient is ground corn, blah.
Nutro is a good food and would be way better. You could also try Canidae, Wellness, or Solid Gold. They are all good foods. My dogs personally get Canidae and are now also given some raw along with it.
4-5 cups is to much feed. My Newfie didn't even eat that much and he was a giant breed dog.
Personally, I would explore every other avenue before I considered drugging my dog. In some cases they are good, but more often than not it is done more for our own convience rather than for the good of the dog. Medications should be the LAST resort.