Unfortunately, Hill's and Medi-cal both are very high in grains IMO. I know that the very first ingredient in every Hill's formula I've ever looked at is corn. Grains will aggravate sensitive stomachs and intestines.
My son's newf had almost constant diarrhea when he was a pup, and he would not gain weight. All his bones stuck out. My vet also treated for Giardia, several times - with no improvement. I had tried a few different foods - so I went back and looked at the ingredients for each of those foods and found that they all had a common ingredient - barley. Suspecting an allergy to barley, I found a high quality food with no barley, and the problem went away. He's still a bit on the lean side (he's almost 5 yrs old now) but he's not scary skinny anymore.
Livin in a Newfie Drool Zone