Tunicamycin reduces wool growth by slowing the mitotic activity of wool follicles

Reductions in wool growth have previously been observed in ewes exposed to low levels of corynetoxins, the causal agents of annual ryegrass toxicity. In this experiment, tunicamycin, a commercially available and closely related toxin, was infused into an isolated area of skin on the abdominal flank. Eleven sheep were continuously infused for 5 days with saline on one side and a total dose of either 35 or 350 mu g tunicamycin/kg affected skin on the other side. Both fibre length (P <005) and fibre diameter (P <0.01) were reduced by tunicamycin treatment. Cell division in the wool follicle bulb was also reduced by tunicamycin (P <0.005), indicating that the toxin is able to have a direct effect on the follicles and their ability to produce wool. The permeability of the vascular system increased in the skin tissue treated with tunicamycin, but only at the highest toxin dose (P <0.05); therefore, poor nutrient supply to the follicle may be a minor contributor to reduced wool growth. The direct effect of tunicamycin on the wool follicle explains why wool growth is reduced by low levels of corynetoxins independently of, and prior to, effects on the whole animal.