food brand quaility

Question
I am feeding my 3 year old female spayed lab Authority lite chicken from petsmart but was thinking of swiching to Purian one overweight large breed... I wa wondering what you think of this food? This link entails what exactly is in the food and percentages >http://www.purinaone.com/products_dog_lrgbreedhw.asp

I'd like to swich because it is slightly less expensive and is more readily avalible...if I run out I can run to teh lcole co-op and grab a bag of the purina one. Will the change of food shorten her lifespan? I've heard expensive foods lenthen lifespan but pruina one is still much better then dog chow/grocery store brands/peddigree, thank you for your advice.

Answer
I think all the talk about ingredients is mostly marketing hype designed to extract more money from those willing to pay more.  Over and over again, I have challenged people on open forums to give me some proof of their claims like dogs will live longer on expensive foods.  I have received abuse, links to sites with highly emotional condemnations of ingredients, but never a reference to any controlled testing showing the more expensive chow was better for dogs.  The nutritional needs of dogs are well known.  Large companies have the resources to analyze their product to make sure what the dog needs is there in carefully balanced amounts.  Why do you thing they all contain so many ingredients?  Each one is there to bring something the dog needs.  In addition, most dog foods, including the Purina, are tested in actual feeding trials.  Some of the more expensive brands are distributed by small dealers as a second source of income.  Some of those people post to websites without revealing that they profit from the chow they recommend.  I swear I don't work for Purina.  If I did, I might push one of their more expensive grades.   

I am sure you have read of the horrors of ''by products''.  By products are the internal parts of the animal.  At the processing plant, all the nutritious insides including the organ meats are removed.  They are sold to the commercial dog food producers.  Have you ever seen a predator eat a kill?  What do they eat first?  Right, all those nasty byproducts that go into some commercial dog food.

The one objective thing is the smaller, firmer stools that are easier to clean up the concentrated, meat based chows produce.  I saw a big difference when the dog guide school switched from the regular Purina to Pro Plan.  My first reaction was that you didn't clean it up, somebody might step on it and hurt their foot.  Purina 1 fits in-between the 2.  I was actually feeding it to our friends' couple dogs last month when we kept them for a weekend.  The store was out of Pro Plan, and they had bought Purina 1 instead.  I don't remember any big difference.  Incidentally, one of the dogs was extremely valuable breeding stock belonging to the dog guide school.  

When you do switch, work the new chow in over about a week.  Any sudden change in diet can cause digestive upsets.  

You may find this interesting, http://ezinearticles.com/?Has-Your-Packaging-Gone-To-The-Dogs?&id=166308

It was posted on a dog forum.