Wool production of Romney ewes and its relationship to cortical cell size

Abstract

Seven Romney sheep which had different feed-to-wool conversion efficiencies were pen-fed for 9 months. Periodic measurements were made of fibre and cortical cell dimensions from clipped wool samples. Wool production did not differ significantly between high- and low-efficient groups of sheep. Cortical cell volume was not significantly correlated with fibre length, fibre diameter, clean wool production, or the previously determined conversion efficiencies of these sheep. It would appear that differences between sheep in fibre volume were due to an increase in the number of proliferated cells entering the fibre cortex. These findings preclude the use of cell dimensions in breeding programmes as indicators of high wool production or pioduction efficiency. Cell length and diameter increased when wool growth rate was declining, and this is believed to be associated with a rapid decline in mitotic activity. It is suggested that increases in mitotic activity may result in lengthwise compression of differentiating cells. During periods of the year when mitotic activity is low, cellular compression within the follicle bulb will be at a minimum. This is postulated as resulting in a larger cell size in the winter.