Effects of nutritional interventions on feathering of poultry - a review

Feather cover of chickens can be influenced by many factors, including direct or indirect nutritional factors. Direct dietary factor effects are levels of protein/amino acids, vitamins, minerals and mycotoxins. Indirect nutritional factors will impact feather cover through their effects on feather pecking behaviour. Since feathers contain 89-97% protein, the supply of dietary amino acids plays a critical role in feather development. Particularly in the juvenile phase of broilers and breeders, low dietary crude protein intake can negatively affect feather quality. Especially the sulfur-containing amino acids methionine and cystine are indicated as necessary for the synthesis of feather keratin. Dietary deficiencies of these amino acids have been shown to result in rough feathering, as indicated by body feathers sticking out from the body, or malformed cover feathers on the wings of young and older birds. Deficiencies of vitamin E and selenium might lead to depigmentation and shorter shafts of wing feathers, whereas deficiencies of other vitamins can lead to slower feather development and swollen tip of down feathers. Mineral (zinc, tin, vanadium, chromium, nickel) deficiencies could result in delayed feather development, frayed feathers (zinc) and blisters on the shafts. Mycotoxins in the feed have been shown to cause sparse covering of feathers and sticking out of feathers from the body. In an indirect way, nutritional aspects can also affect feather cover due to feather pecking in chickens. There is strong evidence that a (very) low crude protein content (<13%) of the diet increases injurious pecking in laying hens. On the other hand, a low energy content of the diet might decrease mortality of laying hens because the dilution of the diet increases eating time. Adding roughage (maize silage, barley silage or carrots) to the daily feed decreases injurious pecking behaviour and increases plumage condition of laying hens. Adding tryptophan to layer diets reduces incidences of feather pecking, because this AA contributes to serotonin turnover in the brain, which is largely related to bird behaviour. Addition of (coarse) insoluble non-starch proteins has been shown to increase gizzard weight and its contents and to prolong mean retention time in the foregut, which is an indicator for higher levels of satiety and a reduced motivation to peck. This chapter gives an overview of the direct and indirect relationships between the effects of nutritional interventions on feathering of poultry.