Dog food bought at Vets are absolute garbage. The vets are only out to make a quick buck. It is expensive and full of shit. Do a search for Hill's brand dog food...expensive and tons of bad reviews. The only real way i found this out is because my dog had allergies to certain ingredients. I googled what my dog's problem could be and the type of food he was eating and what I read really scared me. I went to the vet with this info and he was suggesting all kinds of crap he was selling (try this, try that) and nothing was working.
So i went off on my own to do some research, went to Global Foods, spoke to some of the sales team in there and came out with Acana Pacifica. Problems went away...he was allergic to grains. Since then i've tried different Acana flavours and have now moved on to some other brand i heard was good just to give the dog a little break from the same old. He loves it...moral of the story...buy food where you actually understand what is written in the ingredients "by product" = bad...oh ya, and most vets are only out to make a buck and that includes bullshit vaccines.