Instead of having grit in the widowhood cocks try making a titbit from 1/2 seed mixture 1/2 grit and 1/2 clay block and feed by giving a pinch in the widowhood boxes after eash feeding session
As soon as your young birds are old enough to be parted try introduce a little rice in there deit. Rice is jam packed with carbohydrates. And are great for your racing pigeons.
Try adding Yogurt to the drinking water it will keep there guts healty ,Bio Yogurt.