New Concepts for the Functional Maturation of the Bovine Claw: Endothelial Biology, Angiogenesis and Ageing

Abstract

Introduction: Endothelial dysfunction and impaired angiogenesis are connected to ageing. However, the mechanisms involved in age‐related alterations are not fully elucidated, whereby reduced VEGF‐expression and decreased mobilization of circulating endothelial progenitor cells are suggested as possible causes. When cultured in vitro, endothelial cells often enter a growth arrest phase called ‘cellular senescence’ that is consistent with many changes in age‐related vascular disease. Based on the decreasing lifespan observed in high yielding dairy cows, a hypothesis has been formulated that these cows, due to their enormous metabolic performance, show an accelerated process of ageing, resulting in typical production‐related diseases, particularly lameness. As a basis for further research into the role of endothelial cell biology in high producing cattle, the aim of this study was to set up a model of endothelial ageing. As a first step, the role of angiogenesis in the functional adaptation of the microvasculature of the bovine pododerma was examined.Material and methods: Scanning electron microscopy of vascular corrosion casts of healthy juvenile and adult claws as well as pathologically altered claws, and routine light microscopy of pododermal serial sections was compared to an in vitro model of angiogenesis based on cultured bovine microvascular endothelial cells. For detection of angiogenic molecular control mechanisms effective in both, the pododermal system and our cell culture model, lectin‐ and immunohistochemistry as well as RT‐PCR were carried out.Results and discussion: In the adolescent and adult claw, sprouting and intussusceptive angioadaptation was demonstrated. Evidence of angiogenic processes was also detected in the pathologically altered claws. Immunolocalization of angiogenic factors within the dermo‐epidermal system of the claw was established. The detected angioadaptation may be visible expression of the increased metabolic demands of the claw caused by the growing body‐weight‐load. Increase of the pododermal vascular density via angiogenesis was also the connectional reparative principle in pathologically altered claws.