Will he be okay? (2o characters) ?

It is supposto rain tonight and I didnt have a shelter for my 3 year old, so I built him a nice little stall in my garage (great ventilation) , I made sure I completely horse proofed it the only straw I had is kind of dusty, I think, and I gave him a hay net a salt lick and tonss of water . I'm worried that when he's done his hay he will eat the straw and get sick, he was a rescue and is under weight by not that much, but I still have to fatten him up a bit , will he get sick if he eats the straw?