By Murray, R. D. and Singh, S. S. and Thrusfield, M. V. and Ward, W.R., ,
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This study describes the role of the changes in weight-bearing on the sole and the effect of endotoxins on the inflammatory response of the corium of the hooves. Three heifers and 2 bull calves 12-18 months of age were used to study weight-bearing. A rubber chip of 1 cm thickness was fixed to the toe of the outer hind claws with a resin, and 2 heifers were kept as controls. The animals were put on a concrete yard for 6-8 h daily and otherwise kept on a straw yard. Six weeks later the animals were slaughtered. Gross pathology showed haemorrhages at the ulcer site and a notch in the dorsal wall was evident. Histopathology of the ulcer site showed parakeratosis and arteriosclerosis of the arterioles. The sole tubules contained non-keratinized material. An ulcer was created in the sole, and a biopsy was taken from the sole and the abaxial wall of the left foot of a further 4 calves of similar age and then 2 mg of Escherichia coli endotoxin was given slowly i.v. Serial biopsies were taken and the animals were killed 5-10 weeks later. Haemorrhages were seen in the wall and sole of the feet, especially the hind feet and were more evident in the bull calf. After 5 days, histological examination showed the presence of non-keratinized material in the tubules of the sole and exfoliation of the epidermal cells. At 15 days the epidermal lining of the lamellae had regenerated and the non-keratinized material was evident in the lamellar horn and the tubules of the sole horn. The number of blood vessels in the laminae as well as in the papillae increased markedly compared with the initial biopsy. After slaughter histopathology of the hooves showed non-keratinised material in the tubules of the sole horn, totally occluded blood vessels and hyperplastic changes in the laminae. It was concluded that laminitis may not correctly describe the lesions seen in the sole in so-called subclinical laminitis. Endotoxin can induce diffuse pododermatitis (laminitis) in cattle and the resultant poor quality horn production may predispose to other sole lesions. Primary changes in weight-bearing can cause vascular changes which may be responsible for haemorrhages at the ulcer site and development of sole lesions
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