Equiniphile's post made me realize I've got to get out there later this afternoon. I am going to leave work early and go cold hose him. He's in his stall with a fan and fresh cold water, but I'm still worried. Heat index here in DC is 110 right now.
My rule of thumb is if its to hot for me then its def. To hot for them. I am in Ky and its been so hot they are covered in sweat by 9 am and miserable even with frequent hosing off and them playing in the creek. My gelding is older so I wont chance it.