Incorporation of L-75Se-cystine in tissue fragments from the matrix of the hoof and the claw--a tool for studying the pathogenesis of laminitis?

Protein synthesis in tissues cultured from the bovine hoof

The mechanical strength of the bovine hoof depends on keratinization of cells in the germinal layers of the epidermis. Histological examination of hoof tissues in calves and young heifers has identified disturbances in this keratinization process which would result in ineffective hoof development and could precipitate lameness. Short-term culture of bovine hoof tissue was used to investigate epidermal keratinization. Cell function remains viable in these cultures. The rate of protein synthesis, measured by [35S]-methionine incorporation, continued for at least 3 h in culture. Radiolabelled proteins in tissue homogenates were separated by SDS-polyacrylamide gel electrophoresis and characterised by fluorography and were representative of the proteins found in hoof tissue. Three prominent radiolabelled bands were identified as keratins and actin by Western blotting. Immunohistochemistry showed that keratin was localised principally in the epidermal layers, and microautoradiography indicated that this was the major site of protein synthesis. Hoof tissues cultured under these conditions provide a useful system for studying the acute regulation of epidermal keratinization.

“Subclinical” laminitis in dairy cattle

In dairying countries worldwide, the economic importance of lameness in cattle is now recognised. Laminitis is regarded as a major predisposing factor in lameness caused by claw disorders such as white zone lesions, sole ulcer, and heel horn erosion. The existence of subclinical laminitis was first suggested in the late 1970s by Dutch workers describing the symptoms of sole haemorrhages and yellowish-coloured, soft sole horn. In an attempt to clarify some of the confusing and often conflicting terminology, the literature on laminitis is reviewed. Disturbed haemodynamics, in particular repeated or prolonged dilation of arteriovenous anastomoses, have been implicated in the pathogenesis of both equine and bovine laminitis. Some characteristics of the vascular system of the bovine claw which may be of importance in the pathophysiology of the subclinical laminitis syndrome are therefore discussed. Clinical observations suggest that subclinical laminitis is a multifactorial disease. The different factors that are or may be involved in its aetiology vary in complexity and severity according to the management protocol of the animals. The possible involvement of subclinical laminitis in claw lesions is assessed.

Bovine laminitis: clinical aspects, pathology and pathogenesis with reference to acute equine laminitis

This review deals with the features of clinical and subclinical laminitis in cattle. Prominent clinical signs of acute laminitis are a tender gait and arched back. The sole horn reveals red and yellowish discolourations within five days. In subacute and chronic cases clinical signs are less severe. In chronic laminitis the shape of the claws is altered. Laminitis is frequently followed by sole ulceration and white zone lesions. Blood tests showed no significant changes for laminitic animals. Arteriographic studies of claws affected by laminitis indicated that blood vessels had narrowed lumens. Gross pathology revealed congestion of the corium and rotation of the distal phalanx. Histopathologic studies indicate that laminitis is associated with changes of the vasculature. Peripartum management and nutrition are important factors in its aetiology. It is hypothesised that laminitis is evoked by disturbed digital circulation. In the pathogenesis of acute laminitis three factors are considered important: the occurrence of thrombosis, haemodynamic aspects of the corium, and endotoxins which trigger these pathologic events.