Age and strain differences in plumage renewal during natural and induced moulting in hybrid hens

1. Replacement of remiges and body-feathers was studied in several flocks of brown and white layers and broiler-breeders under near commercial conditions. 2. Spontaneous moulting of primaries was not circannual in modern laying hybrids; moulting response was more retarded in brown than in white hens. 3. Following induction of moulting by a standard procedure in brown hens, the extent of replacement of remiges increased with increasing age, but even at 81 weeks of age, moult was not completed, but ceased when half of the flock had moulted less than half of the primaries. 4. At comparable age the moulting response was considerably more extensive in broiler-breeders than in layers; moulting was not enhanced in hens that had already started to moult before the induction. 5. Compared to the remiges, the moulting response of the body-feathers was more complete and quicker. However, these results might be influenced by a lower threshold of sensitivity to feather growth-induction of the empty follicles, the cumulative number of which is considerable among the contour-feathers after several months of laying.