A study of the importance of cell size in quantitative wool production

Abstract

Sheep differ in their inherent abilities to convert feed protein into wool keratin (Marston, 1948; Ferguson, Carter and Hardy 1949; Clark, Keshary, Coop and Henderson 1965). Animals processing a high efficiency of wool production maybe characterized by a greater density of active follicles, or by an increased production of fibre volume per follicle. If the findings of Henderson (1953) for Kent and Romney longwools are followed in this experiment, then fibre volume will contribute most to wool production with fibre density having little effect. In this case the cause of increased fibre volume would probably be due to either a faster rate of cellular proliferation within the individual wool follicle bulbs, or to a larger cell size within the fibre.

To date there has only been limited research into the relative importance of mitotic activity (Fraser 1964a; Schinckel 1961, 1962; Short, Wilson and Schinckel 1964; Short 1965) and cell size (Short et al 1964; Short 1965) with respect to wool production. It is generally concluded that there is relatively little differences in cell volume between animals and that cell turnover rate is the major factor influencing variations of production. However, it is also recognised that both these factors will be influenced by plane of nutrition (Schinckel 1962; Short et al 1964; Short 1965).

Ultimate cortial cell volume is a measure of cell growth from the time of its proliferation, through differentiation and keratine formation, until it is fully keranized. Therefore factors which will affect cell growth during these phases will also affect the final cell volume.

In this experiment a number of Romney Marsh sheep specially selected to provide a range of feed:wool conversion efficiencies were pen-fed inside for 9 months. It was planned to measure the productive characteristics of these sheep, to note any variation in cortical cell volume both between sheep and with time, and if possible to obtain a reasonable estimate of relative mitotic activities.

The technique employed, and the analysis thereafter, were not intended to be as simple and as rapid as would be required of a practical method for large-scale identification of efficient wool-producing sires. Rather they were developed with the purpose of obtaining an accurate relationship between the internal and external components of wool production, and of determining any differences between individual animals.