Review Current research and theories on the pathogenesis of acute laminitis in the horse Simon R. Bailey a , Celia M. Marr b, * , Jonathan Elliott a a Department of Veterinary Basic Sciences, Royal Veterinary College, North Mymms, Hatfield, Hertfordshire, UK b Veterinary Clinical Sciences, Royal Veterinary College, North Mymms, Hatfield, Hertfordshire, UK Accepted 1 July 2003 Abstract A large number of studies have been undertaken in recent years aimed at furthering our understanding of the complex mech- anisms underlying the common and debilitating condition of acute laminitis in the horse. Many of these studies have either rein- forced or cast doubt on previously held theories on the pathogenesis of this disease, while others have suggested new mechanisms which may play a key role in its development. This review seeks to put the current hypotheses into the context of this recent body of evidence. While a unifying theory may not yet seem to be achievable, this review demonstrates that most of the current theories are not mutually exclusive. Studies utilising in vitro and in vivo models of the disease, particularly addressing the areas of inflammation, haemodynamic disturbances and enzyme activation in the hoof, as well as the preceding events occurring in the hindgut, have helped to explain many clinical observations of the disease and may possibly lead to more effective therapies and means of prevention in the future. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Horse; Laminitis; Pathogenesis; Ischaemia; Amines 1. Introduction Laminitis continues to have widespread implications for equine welfare. This has been highlighted by a recent survey in the US which found that 13% of horse owners/ operations reported problems with laminitis in their horses over the previous 12 months (USDA, 2000). Similarly, a survey involving 113,000 horses in the UK found a prevalence of 7.1% (Hinckley and Henderson, 1996). Although it is accurate to say that the precise causes of acute laminitis in the horse are not yet fully understood, and there are still a number of different theories as to the pathogenic mechanisms involved, this is a fast moving field of research in which a large amount of recent work has improved our understanding of this common condition. The pathogenesis of acute laminitis, in particular its link with disturbances of the hindgut following access to lush pasture, has been a subject of fascination and frustration ever since horses have been kept on Ôim- proved pasturesÕ. There are many other potential factors that may contribute to the onset of this condition, nevertheless, pasture-induced laminitis appears to be the most common aetiology in the UK (Hinckley and Henderson, 1996). It has become increasingly apparent that allowing horses and ponies access to excessive amounts of certain types of carbohydrate is likely to trigger changes in the hindgut precipitating this disease. The trigger factor(s) released from this process have yet to be elucidated, however various proposed candidates are now being investigated, and more knowledge has been gathered about the biochemical and functional responses within the foot which these mediators may initiate. In addition, significant advances have been made in the understanding of the form and function of the tissues of the foot, particularly the dermal and epi- dermal lamellae. The Veterinary Journal 167 (2004) 129–142 www.elsevier.com/locate/tvjl The Veterinary Journal * Corresponding author. Tel.: +44-7717-431-749; fax: +44-1707- 652090. E-mail address: celia.marr@rossdales.com (C.M. Marr). 1090-0233/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S1090-0233(03)00120-5