"Grain corn" refers to a type of corn that is grown to produce food products, such as cornmeal and cornflour. It is not the same as the sweet corn we eat as a vegetable. Full definition
Unfortunately, this puppy food has whole grain corn as its first ingredient, rather than a meat. (herepup.com)
Whole grain corn contains about 5 percent protein (this can vary depending on different factors), 9 percent fat, and about 86 percent carbohydrates. (dogfoodinsider.com)