According to Bell and Weaver (2002); ‘Moulting is a natural process in adult birds to renew feathers annually under hormonal influence’.
Follett (1973) provided a comprehensive review of natural moulting, which is induced by environmental and nutritional cues, with decreasing day length initiating gonad regression (Follett, 1973). Temperature variation and photoperiodic changes induce circadian and circannual rhythms (Berry, 2003). Manifested by the neural and endocrine systems, these rhythms cause physiological processes resulting in a moult.
These rhythms can produce migratory fattening and restlessness (Follett, 1973). One observable change for naturally moulting birds included voluntary reduction in food intake or spontaneous anorexia. The ability to tolerate prolonged fasting resulted in almost 20% body weight reduction, loss of plumage, and reproductive quiescence (Mrosovsky and Sherry, 1980). Some physiological mechanisms observed in natural moulting are noted in induced moulting as well. In the United States (U.S.), induced moulting by feed deprivation began during the early part of the 20th century as a solution to economic challenges of decreased egg production in commercial layer flocks toward the end of the first laying cycle.
The following review discusses the influence of feeding strategies in the moulting procedure.
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