Growth of the N-type fleece.

Abstract

The rates of growth of wool fibres are compared between normal and N-type Romney Marsh sheep. The three types of follicles — primaries and first- and second-wave secondaries — form their fibres at rates of the same order in normal Romneys. The N and nr genes cause an increase in the rate of growth of the early, primary fibres, and a decrease in the rate of growth of late fibres, having no marked effect on fibres initiated between these two periods. It is argued that. the primary effect of these genes is to increase the efficiency of competition of the early initiated follicles, resulting in an increased growth rate of their fibres, which, owing to competition between follicles, results in a proportionate decrease in the growth rate of the late fibres.