Pigmentation, impression hardness and the presence of melanosomes in bovine claw tissue

The physical properties of hardness and dry matter and the histological characteristics of dermal and epidermal tissues were investigated in lateral and medial claws obtained post mortem from mature crossbred female cattle. Claws containing pigmented (n=22) or non-pigmented (n=22) coronary wall horn were studied. Impression hardness, measured on the dorsal border of claws, proximo-distal at intervals of 5 mm from the lower perioplic line was shown to increase to the 20 mm lower site. Similarly, in comparison with values for pigmented horn, pooled measurements for non-pigmented horn showed greater hardness from the lower perioplic line to the 40 mm lower site but were not different for subsequent measurements towards the distal edge. Differences in values recorded for sole and heel and for coronary wall horn measured under the distal edge were not different for claws varying in coronary horn pigmentation. The absence of differences in dry matter at measurement sites suggested that differences in impression hardness values were not caused by variation in water content of horn. Histological examination of pigmented claw wall horn and underlying soft tissue showed pigment-containing cells in the coronary epidermis but not coronary dermis or in dermis or epidermis of laminae. Pigmentation appeared concentrated in melanosomes in cells along the basement membrane and was present uniformly throughout the epidermis and in cells lining horn tubules. There was no pigmentation detected in the soft tissue epidermis of claws selected visually for non-pigmented wall horn. The presence of melanosomes in epidermal cells from the pigmented coronary region was demonstrated by electron microscopy. The results suggest that pigmentation in the coronary region is associated with reduced initial development of hardness. The possible antagonism between antioxidant properties of melanins and requirement for an oxidative environment for disulphide bond formation in the cytoskeleton of horn cells is discussed.