Experts suggested an easy way of finding out whether the chickens are being fed correctly.
This is by looking at the floor of the pen to find out whether there are too many or too little feathers scattered around, or looking at the chickens to see whether some of them are already bald due to pecking by the other chickens. The underlying principle is, that the chickens will eat their feathers to get the protein they need. The chickens feathers and their fellow chicken's skins are good sources of protein.
Tips showing when chickens are supplied with more protein are: when the chickens are bald, when chickens are suffering from wounds inflicted by other chickens that peck on them and when less feathers are scattered around. These techniques could easily be adapted to large scale commercial operations where collection of accurate weight and conversion data would not be possible.
Source: Greenfields, July 1980