Developing feathers

Oblique section of a newly developing feather of a Muscovy Duck (Cairina moschata) (HE)

Feathers are replaced periodically. A new feather is produced by the same follicle; it is the initiation of this new growth that normally ‘pushes the old feather out’.

Feather development is an extremely complex process in which many elements happen at the same time:

• The development of a ‘column’ of epidermis out of the epidermal collar and the differentiation of this outer epidermis consecutively into barb ridges, barbs and barbules, rachis and calamus;
• The formation and regression of an inner pulp and pulp caps out of the dermal papilla and the covering epidermis;
• Keratinisation and pigmentation of the feather.

At the micrograph above, the blastema is just becoming active: regeneration of a new feather has begun with the lengthening of the dermal papilla. In the epidermal collar, a basilar and intermediate layer can be differentiated from each other.