Breny is exactly right....you will get a TON of answers about food

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I am very serious about what I feed my Snickers. I honestly think I found the perfect food for him. I wanted something grainfree (grains can cause allergies but so can some proteins,) moderate protein level, and no fillers or controversial ingredients. We chose Acana

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Acana is made my ChampionPetFoods which also makes Orijen pet food and Orijen was awarded Dog food Of the Year in 2009.
Acana comes in 3 varieties which is great b/c you can rotate. I truly feel it is one of the best kibbles on the market right now. Snickers LOVES his food and that is wonderful since I'm sure you know how picky Yorkies can be. I also feed raw, but that's a whole nother category

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Many of us use this website for insight on food quality:
Dog Food Analysis - Reviews of kibble
I would recommend only feeding a food that is 4 stars or higher. Acana is 5 stars

6 star foods are higher in protein.
Good luck

Snick & Viv