Factors Influencing Cellular Events in the Wool Follicle

Summary

Factors influencing wool follicle bulb cell mitotic rate (MR), cell migration, and cortical cell production, were examined. Nutrient supply in general, and sulphur-containing amino acid (S-amino acid) supply in particular, significantly alters MR. The S-amino acids, L-cysteine (2 g/day) and L-methionine (2.46 g/day), alone or in combination, increased MR by 35% (P<0.05); there was little difference between treatments. Infusion of the lysine-deficient protein zein (80 g/day) into the abomasum depressed MR by 60% (P<0.05) and increased cortical cell length by 5% (P<0.05) while cortical cell volume was unaltered. Sheep differing genetically in wool-producing capacity were offered a low, followed by a high, plane of nutrition. Increasing nutritional level resulted in increased fibre growth, mitotic rate and bulb volume, a reduction in the proportion of orthocortex, and variable effects on cortical cell volume. The proportion of dividing bulb cells contributing to fibre cortex was unaltered by nutrition but did appear to differ between genotypes and contribute to genetic differences in fibre production per follicle. Thyroidectomy depressed MR by 22% (P<0.05) but had little effect on cortical cell size. The regulation of follicle bulb cell division and fibre growth is reviewed.