Abstract
Growth of a contour feather on a dorsal spinal tract of Japanese quail was investigated using a logistic model, in which feather length is determined by two factors, growth rate and growth period. Final feather lengths were constant under most experimental conditions including those under which the growth rate decreased while the growth period increased. Another experimental condition was discovered in which a feather elongated owing to an increase in growth period.
Once a feather had fully grown, its length remained constant. After plucking a feather, a new feather grew and its final length was correlated with the old one. Shortening a growing feather by cutting off a distal part did not affect its growth pattern. In addition, shortening a fully grown feather by cutting off the distal part did not activate its follicle. Plucking a feather during growth stopped and erased the present growing phase and initiated feather growth from the beginning to form a complete feather. Repetition of plucking four or five times did not affect the final length of a feather, but did decrease the growth rate, which was complemented by an elongation of the growth period. Feather formation under a short photoperiod condition (8L:16D) resulted in a longer feather which resulted from elongation of the growth period while the growth rate remained constant.