Feather eating is a habit they can get into and you can stop them from doing it by using anti-peck sprays to make the feathers taste unpleasant. When there is a lot of feather pulling, it’s worth checking to make sure that it’s not being caused by the irritation skin parasites cause. Dirty vent feathers, lots of scratching and dustbathing, hunched or withdrawn hens and soft shelled eggs are often indications that your hen has an infestation too. Mites can’t be seen easily with the naked eye but they leave the skin looking sore, red and featherless. Lice can be spotted quite easily. The hot spots where lice tend to hide are around the vent, under the wings, round the abdomen and chest and the neck area. Ruffle the feathers against the direction of growth and look for little scuttling creatures or tiny cream eggs stuck to the feather shafts. If you come across any, you can get louse/mite powders from various sources including poultry feed suppliers/farm suppliers and some large petshops. Apply it to all your hens and repeat the treatment after a week to catch any eggs which might have hatched out.
Red Mite don't live on the hens but live inside the hen house and move onto the hens during the night so if you check in all the corners, pull out roosting bars if you can, check around the roof for signs of infestation. They aren't particularly easy to spot as they are only about 1mm long and are grey before feeding and red after due to the blood that they suck from the hens and this blood sucking can lead to anaemia and lethargy. If you have a red mite infestation in your chicken coop, you may see tiny blood spots on the hens eggs and there may also be a greyish powder which can be seen around the ends of the perches. If you wipe the undersides of the perches with a clean white paper towel and find red streaks on it, this will show that there are red mite in the coop. Spreading Vaseline or nappy cream on the ends of the roosting bars and in the ledges where these bars sit can trap red mite too as they head for dark crevices during the day and any which do become stuck in the sticky cream can be wiped or washed off. To treat an infestation, you will need to remove everything from the coop which can be taken out and spray with a proprietary red mite treatment. Steam cleaners are also very effective for eradicating lice and mites from coops.
If the skin is red, sore or broken, separate the injured hen straight away and you can use Veterinary Wound Powder on her to help stem the bleeding and promote healing. Hens are morbidly attracted to the colour red and will peck at wounds until they are in a dreadful state if nothing is done so Gentian or Purple Spray is very effective as it stains the skin purple and this makes it a much less obvious target for the bully. You can also use Stockholm Tar which acts like a sticky black plaster, deterring further pecking whilst allowing the wound to heal underneath. With my own hens, we have found that some of the anti-pecking sprays cause the feathers to clump together though and this can make them more of a target for a bully so a puff of Veterinary Wound Powder or even household cornflour in an emergency disguises the sore area effectively and helps stop bleeding. If any hen develops a wound of any kind, remove them and allow it to heal for a few days before reintroducing them to prevent the wound being pecked.
Feather eating can be the result of a dietary deficiency so you may find that feeding the hens tuna canned in spring water (not brine as it's too salty for them), hard boiled eggs or live mealworms can help as these are rich in protein and may help if they are suffering from a dietary imbalance. We have read that hens who have diets where the amino acid "methionine" is missing or at an inadequate level, this can lead to hens pulling their own feathers and eating them to try and correct this imbalance. Layers meal supposedly contains this amino acid but it's recommended that if you have a problem with hens eating feathers, don't give additional grains such as corn or wheat to them as this can mean that the amount of methionine can be inadequate for providing growth and feather development. If they have corn or grains as well as their layers meal, it might be worth leaving them out of their diets for a week or two and see if it makes any difference. Make sure that they also have Poultry Grit available at all times. Also give them plenty of leafy green vegetables such as cabbage, kale, broccoli, spinach etc tied up in the run if they don't have access to grass.