I've been reading up on the origins of dog food, i've found that basically the whole thing started when they realized that they could make money off of the leftover stuff that they couldn't feed to people.
basically anything that's not USDA approved for people was totally fine to give to dogs, so they'd mash it all up together and have kibble.
there used to be bones, hair, rotten organs and carcass, rotten grains, and more. i did know that there can be a certain level of things like mouse poop and hair and other things like that in people food, so just imagine what they are ok with in dog food.
we decided pretty fast that we would go all natural or serve our dog people food, if i can't eat it, she should have to either. i didn't like seeing all the chicken meal, or chicken by product in my dog food labels, even holistic food had terms i was not comfortable with, so that's why we choose raw, and after realizing that it was completely cheap, convenient and easy to make and store, and that she wouldn't eat very much anyways, we made the choice to start her out right with home made "people food" diet.
anyways, here is a link to some sites of the history of dog food, they talk about canned horse meat and other gross things i wouldn't feed my dog.
History of Dog Food Another dog food history site
This stuff will just make you sick, but it's great to know so you can make a choice that works for you. Point that i'm making here, really check into what's in those bags of kibble rather than assume that it's suitable for dogs because it's called dog food.
And in closing, if you don't like what you see, try the link on here about home made diets and see if one of those is the right one for you and your pup!!
Hope you have a fabulous day, and keep the research going, it's the only way you'll ever find out the truth behind things that seem so normal.