ESTIMATING DENSITIES OF ORIGINAL AND DERIVED SECONDARY WOOL FOLLICLESIN THE SHEEP

A simple method to determine densities of original secondary (N-SO) an d derived secondary follicles (N-SD) in the skin of the sheep, using c onventional histological procedures, is described. It is based on the observation that primary and original secondary follicles develop at s eparately identifiable sites in the skin. Thus, counts of pilary canal s provide estimates of N-P+N-SO. Primary follicle and total follicle d ensities (N-P and N-P+N-SO+N-SD) were obtained by published methods. F rom these values, N-SO and N-SD were derived. Four selection lines of sheep with different total follicle densities were studied. The result s show that N-P and N-SO are relatively constant in the sheep lines, d ifferences in follicle densities being due to the derived secondary fo llicles.