I don't think there's anything wrong with grit - in fact it's necessary if you're giving grains. However, I do know from experience that given anything new, chickens are apt to just chunk it down their throats and pay the price later. When I'm starting birds on grit from a more controlled environment, i always offer a little at first - then more a day or so later, then more, etc. I'm actually doing this with our poults, goslings, and chicks now as they're transitioning to where they'll have access to grass. (Unfortunately the way things are here, we can't start them out that way...)
So when you do that, they can often get too much grit and get their crop backed up. (That's the smell you smelled - good instincts).
When this happens, their entire digestive tract slows as well. So you'll want to remove the grit and grains and only feed very easily dissolved foods for a few days while you get your flock back on track. Pellets, crumbles, some yogurt is nice to replace their now shocked gut bacteria, a little egg yolk, non-sweetened applesauce in moderation, a bit of *organic* apple cider vinegar in their water also helps the acidity of the crop and gut return to normal. (Backed up crops change pH because of the 'going bad' of the food that's not moving through the system.) I use 1 teaspoon per half gallon of water.
Then slowly introduce the grit and grains again. And tell that silly roo to not hog so much next time!
In the mean time, please let us all know if you need any more support and how your boy is doing. Thank you.
