Personally, I think you should feed them all Innova Evo. It's for all life stages, sizes, breeds, etc... just tailor it to fit each dogs needs, as far as amount and any additions you might want to add (veggies, meats, RMB's, etc). Gonzo loves Evo and has done really well on it, he only needs 1 cup per day to maintain perfect weight at 40 lbs. Canidae is also a good food for all life stages, and much cheaper than Evo. I really don't buy into all of the different formulas, such as large/small breed puppies, reduced calories, active, etc. The only real reason I've found for all of the various formulas is the company's make more money ... thats my take at least!! Good luck with your St Bernard! I hope you're able to adopt him, I lurve his name =0)