If broiler breeders are lacking sufficient amounts of sulfur amino acids (cystine and methionine) in their diet, they will start looking for these amino acids by eating the feathers from the floor.
If they are seriously deficient on this, they even will start pulling feathers from eachother, to get enough sulphur. This behaviour can result in feather pecking and if it goes too far into cannibalism.
When this happens, immediate action must be taken to adjust the diet (increase the sulphur amino acids), because too late reaction can result in inprinted behaviour, bad feather coverage, severe stress on the birds and severe occurance of mortality due to cannibalism.
If the flock is nervous or signs of pecking are observed, the first thing to do is to check if there are feathers on the ground, and then especially the smaller feathers. In any case it should be a standard routine to check the amount of feathers in the litter.
If there are no or only a few feathers present in the litter, observe the behaviour of the birds, and if there is any indication for feather licking, feather pulling or feather pecking, immediately contact a nutritionist to check the diet and see if there possibly can be deficiency of sulphur amino acids.