Corn will not "warm" your birds.Corn, chilled or dried, generates digestive heat so while it's chilled component may cool initially the corn itself will actually warm your birds. Stick with chilled dark leafy greens (light on any spinach) chilled melon and fruits...frozen for those really warm days of summer. Save the corn for the winter when they need the extra heat and then give it to them toward the end of the daylight hours to help them warm at night.
The story that Corn will make your birds/animal hot is a misunderstanding of the term "HOT" when referring to livestock.
The term HOT simply means High Energy as in Corn is a High Energy feedstuff.
You can look at this way also, most poultry feed contain 50 to 70 percent corn and not one chicken has ever suffered from Heat Stress wile eating a high Corn diet.
Yes Corn produces some "heat" BUT so does everything else that a chicken eats.