A cell biological approach to studying lameness in the dairy cow
This thesis describes a cell biological approach to studying lameness in the dairy cow. Lameness has been associated with altered keratinisation of the epidermis of the bovine hoof. Claw tissue was obtained by an in vivo claw biopsy technique. The biopsies were cultured in the presence of L-[35S]-methionine and [3H]-thymidine for measurement of protein synthesis and cell proliferation respectively. The influence of nutritional and environmental stressors on keratinisation in the claw was investigated. Protein synthesis was found to be significantly higher after challenge with these factors. It was not clear, however, if this was an effect of challenge or the biopsy procedure itself. Physiological and endocrinological changes associated with pregnancy and lactation also appeared to have an effect on claw keratinisation. In a long-term developmental study of first-calving heifers changes in cell proliferation and protein synthesis were related to reproductive state. A dramatic seasonal effect on claw cell biology was also demonstrated. The keratinocytes were actively proliferating and keratinising during the summer months but were quiescent during the winter. A final study investigated the cell biological changes which occur in the claw during the onset, development and recovery stages of weight-bearing challenge and the effects of concrete flooring. During challenge cell proliferation increased significantly in claw subjected to weight-bearing. The tissue may have been responding to challenge, however, the biopsy procedure itself could also have had an effect due to the short-time period between samplings. To conclude, altered keratinisation in the claw may be related to physiological and endocrinological changes associated with season and reproduction. However, changes in management may also be important and further investigation is required.