Young chickens moult twice during their first year of life. During the first few weeks of life the soft down feathers are replaced and later young feathers are replaced by adult feathers.
In good health a chicken will moult annually starting during September, which could go on for several months. Feathers die and are replaced; however there may be some delay which results in bald patches as new feathers develop. Moulting takes considerable energy placing the chicken vulnerable to ill health. Hens do not lay and cockerels do not breed during moulting season. Antiparasite treatments should not be used during this time as it may interfere with healthy feather development.