Risk factors for equine laminitis: A systematic review with quality appraisal of published evidence
Introduction
Laminitis is a disease of the foot which results in pain, lameness and loss of athletic performance (Herthel and Hood, 1999, Hood, 1999). The disease poses a threat to all Equidae. Laminitis affects a significant proportion of the general equine population, as highlighted by a recent review of 69 frequency publications (Wylie et al., 2011). Laminitis is known to have a complex and multifactorial aetiology of vascular, inflammatory, metabolic, endocrinopathic and/or traumatic/mechanical origin (Hood, 1999, Pollitt, 2010, Pollitt and Visser, 2010). The disease process, irrespective of its origin, ultimately results in lamellar degradation of the suspensory apparatus of the distal phalanx (SADP), leading to clinical signs of overt foot pain (Collins et al., 2010a).
Although many factors are considered to affect the risk of laminitis (Heymering, 2010), epidemiological studies into risk factors for naturally-occurring laminitis are limited (Bailey et al., 2004), and the results are inconsistent and disputed in areas such as signalment (Dorn et al., 1975, Slater et al., 1995, Polzer and Slater, 1996, Alford et al., 2001, Parsons et al., 2007, Menzies-Gow et al., 2010) and seasonality (Dorn et al., 1975, Polzer and Slater, 1996, Menzies-Gow et al., 2010). The reasons for the conflicting results are unclear. Preventive and therapeutic strategies and interventions therefore remain empirical and based largely on anecdotal rather than evidence-based medicine.
Intrinsic risk factors (for example, breed, age and gender) and extrinsic risk factors (for example, nutrition, exercise and health status) may differentially influence risk. Whilst some risk factors can be directly controlled or avoided through changes in general management practices, others cannot. Nonetheless, comprehensive knowledge and understanding of the risk factors for laminitis are needed in order to formulate new hypotheses regarding causal factors and the disease processes that can be tested scientifically. Additionally, identification of modifiable risk factors should allow development of enhanced preventive measures and the provision of new management guidelines for owners that should decrease laminitis occurrence within the horse population.
Systematic reviews are generally accepted as the ‘gold standard’ method for appraising quality of evidence, and PRISMA1 (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines have been produced to improve the systematic review process (Moher et al., 2009). Interrogation and evaluation of previously reported evidence will aid in elucidating potential disease mechanisms, allow identification of modifiable risk factors and appropriate intervention measures to minimise the disease threat.
The aims of this study were (1) to identify previous research providing information on risk factors for naturally-occurring equine laminitis; (2) to ascertain its scientific robustness, and (3) to identify what aspects of equine laminitis risk factors require further epidemiological investigation.
Section snippets
Materials and methods
This article is written in compliance with the PRISMA statement (Liberati et al., 2009, Moher et al., 2009). The protocol is described within this paper alone and was not registered with PRISMA.
Quality assessment
The initial database search identified 413 potential laminitis risk publications (Fig. 1). After adjusting for duplicates, 388 remained. Of these, 14 publications were excluded after reviewing the title and abstract because they were not written in the English language, or were books. The full text of the remaining 374 publications was examined in detail. Only 12 publications met the inclusion criteria for the systematic review. The majority of discarded studies failed to contain any
Discussion
This was the first study to perform a systematic review of published evidence of risk factors for naturally-occurring equine laminitis.
Overall the quality of risk factor publications was reasonable, and higher than a similar quality assessment of publications reporting the frequency of the disease (Wylie et al., 2011). Most publications (>82% overall, and 100% of the top six) aimed to identify laminitis risk factors and this focussed approach may have improved scores. Publication bias may have
Conclusions
This article summarises previous published research regarding risk factors for laminitis. Many of the publications focussed on easily measurable factors, such as signalment or season. It is important to re-focus investigations on risk factors of greatest potential importance to help us reduce the impact of the disease in the future through modifications and their evaluation by intervention studies. It remains appropriate to continue to investigate non-modifiable factors whilst there is a lack
Conflict of interest statement
None of the authors of this paper has a financial or personal relationship with other people or organisations that could inappropriately influence or bias the content of the paper.
Acknowledgement
This study was generously funded by World Horse Welfare.
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