AGE-RELATED-CHANGES IN WHITE WOOL-BEARING SKIN MELANOCYTES

Eighteen Merino ewes either without pigmented leg hairs (6 ewes), or w ith pigmented leg hairs (12 ewes) and associated isolated pigmented fi bres in the fleece, were assessed for wool-bearing skin melanocytes at birth, lamb marking, lamb shearing and hogget shearing. It appears th at both the number of melanocytes and time of their arrival at the ski n epidermis during foetal development determines the likelihood that i solated wool fibres will become pigmented. The sheep with pigmented le g hairs and isolated pigmented wool fibres in the fleece had associate d high concentrations of wool-bearing skin melanocytes at birth. Howev er, variation between individuals, an age-related decline in the densi ty of melanocytes following birth, an increase in melanocyte number af ter birth in some of the sheep, and a low relationship between skin me lanocyte count and pigmented fibre concentration among affected indivi duals, eroded the perceived potential for use of such skin diagnosis f or detecting this wool fault in young sheep.