I was reading Michael Pollan's book The Omnivore's Dilemma when I got my dog, Clyde. So, I was really conscious of food ingredients when I was thinking about what food to buy for him. Guess what is one of the top three ingredients in most dog food? Yep- corn. In addition to being a significant contributer to all the reasons I am uncomfortable with industrial agriculture, corn is also an allergen for some animals. So, I decided that if I wasn't going to eat food that included processed forms of corn or soy, neither were my animals.
There are several brands of dog (and cat) food sold at major pet supply stores which do not include corn meal or corn gluten. Consider really reading the labels of the food you buy. It may be more expensive to buy a different brand, but consider your impact on the health of your animals and of the planet.