steer gets bloaty look

My son's show steer gets this bloaty look to him on his left side, holds a soft air pocket you can feel when run hand on him. He belches a lot. I have gave him probios to no avail. He has never bloated to say, or even been sick at all. He gets 3lbs of showmaker and 7lbs of COB twice a day with all he can eat grass hay and a few lbs of alfalfa. His show is coming up in a couple weeks, currently weighing about 1150.
Just curious how we should feed him show day, or if this will even hold him back in the class at all?

Years ago had on like that and the vet diagnosed it chronic bloat. He said to feed sodium bi carb(baking soda) daily. Don't remember how much but I know you can buy it in 50 pound bags at the feed store if you don't want to buy little boxes at the grocery store.