Laminitis is a common and painful condition affecting adult horses and ponies. It can have serious consequences, frequently resulting in permanent lameness or, in severe cases, euthanasia. Research estimates suggest that the frequency of laminitis ranges from 1.5% to 34%, depending on the population studied, the proportion of horses and ponies, the presence of other illnesses and geographical location. The condition may occur as an isolated episode, although repeated episodes over an extended period are more common. Research conducted in UK veterinary practices has also identified that horses affected by laminitis have a nearly sixfold increased risk of mortality.
Understanding The Different Types Of Laminitis
Laminitis is now understood as a clinical syndrome associated with underlying systemic disease or changes in weight-bearing, rather than a single, independent disease. It is broadly divided into three categories: sepsis-associated laminitis, endocrinopathic laminitis and supporting limb laminitis.
Endocrinopathic laminitis is associated with underlying endocrine conditions that cause insulin dysregulation. Two conditions particularly associated with this form of laminitis are equine metabolic syndrome (EMS) and pituitary pars intermedia dysfunction (PPID), previously known as Equine Cushing's disease.
Research at the Royal Veterinary College (RVC) has concentrated particularly on understanding endocrinopathic laminitis, examining the relationship between metabolic abnormalities, insulin regulation and the development of the condition.
Equine Metabolic Syndrome And Insulin Dysregulation
Equine metabolic syndrome is a collection of clinical abnormalities associated with an increased risk of laminitis. Its defining characteristic is insulin dysregulation, although affected animals may also experience obesity, elevated circulating triglyceride concentrations and changes in adipose tissue function.
Adipose tissue produces hormones known as adipokines, including adiponectin and leptin. Changes in the production of these hormones are among the factors being investigated in relation to metabolic health and laminitis.
Research at the RVC has demonstrated that grazing summer pasture and consuming dietary carbohydrates can produce metabolic changes in susceptible ponies. These changes include worsening insulin dysregulation and the development of hypertension.
Insulin dysregulation can present in three different ways: elevated insulin concentrations at rest, an excessive insulin response following the consumption of carbohydrates, or insulin resistance within body tissues. Researchers have investigated methods of identifying these abnormalities through testing, including the administration of small quantities of glucose powder or corn syrup.
Comparisons between the glucose feeding test and the oral sugar test demonstrated agreement in the majority of animals, with the results corresponding in 85% of cases. Research also established an improved corn syrup dose for identifying insulin dysregulation and examined how withholding food before testing affects the results.
The accuracy of insulin measurements has also been investigated. Different laboratory assays used to measure insulin concentrations in equine blood produced variable levels of agreement, meaning their results cannot necessarily be used interchangeably.
Inflammation, Exercise And Metabolic Health
Further RVC research has examined the relationship between metabolic syndrome and inflammation. Findings indicated that ponies with equine metabolic syndrome had a reduced anti-inflammatory capacity rather than a persistently increased inflammatory state.
This reduced capacity improved following 14 days of regular, low-intensity exercise involving walking and trotting.
Researchers also investigated blood pressure and the function of blood vessels in ponies with metabolic syndrome. Although seasonal hypertension was identified, other investigations did not demonstrate evidence of endothelial dysfunction in these animals.
Another important finding concerned adiponectin, an insulin-sensitising hormone produced by adipose tissue that also has anti-inflammatory properties. Circulating adiponectin concentrations were found to be lower in animals that had previously experienced laminitis.
Lower concentrations were also identified in animals without previous laminitis that subsequently developed the condition within the following one, two or three years. These findings indicate that low adiponectin concentrations may be a risk factor for future laminitis.
An immunoturbidimetric assay was subsequently validated to measure adiponectin concentrations in equine samples.
Research Into The Treatment Of Laminitis
The RVC has also investigated the outcomes of horses and ponies receiving treatment for endocrinopathic laminitis through first-opinion veterinary practices.
The findings showed that eight weeks after the onset of laminitis, 95% of affected animals were still alive, while 59% had returned to being ridden.
Survival was associated with lower body weight, an appropriate body condition and less severe laminitis. Animals without a previous history of laminitis were also more likely to return to ridden work.
The research compared different medical treatments and methods of foot support. No individual medical therapy or foot support approach was demonstrated to be superior to the others in the cases examined.
Understanding The Epidemiology Of Laminitis
Research into the occurrence of laminitis over a six-year period identified several factors associated with its prevalence and incidence.
The highest levels were recorded during May. Researchers also found a positive relationship between the number of sunshine hours and the occurrence of laminitis.
The study identified female animals and lighter animals as having the greatest risk of developing the condition.
These findings contributed to a better understanding of the factors associated with laminitis and the circumstances in which it is more frequently observed.
Diagnosing Pituitary Pars Intermedia Dysfunction
Pituitary pars intermedia dysfunction is a progressive neurodegenerative disorder associated with changes in the normal hormonal activity of the pituitary gland.
The condition involves the loss of inhibitory dopamine input to the pituitary pars intermedia. This leads to increased production of its normal hormones, some of which may interfere with insulin activity and contribute to insulin dysregulation in certain animals.
Diagnosis involves measuring concentrations of adrenocorticotropic hormone (ACTH) in plasma.
RVC research examined two laboratory assays validated for measuring ACTH in equine samples. The findings showed that the two methods produced different absolute values. Researchers also identified that other hormones originating from the pituitary gland may interfere with results obtained using the chemiluminescent immunoassay.
Managing Obesity In Horses And Ponies
Obesity is another characteristic associated with equine metabolic syndrome, while some animals affected by PPID are also overweight or obese.
Weight-management strategies are therefore used to help reduce body weight in affected animals. These approaches frequently include restricting access to pasture through changes to grazing arrangements.
RVC researchers validated the use of accelerometers to monitor physical activity in horses. These devices were subsequently used to investigate how standard and smaller paddock sizes influence the amount of time horses spend grazing and moving.
Further research is also examining how different strip-grazing arrangements affect physical activity in ponies.
The Science Behind Hoof Growth
Understanding normal hoof growth is an important part of investigating how diseases may affect the development and structure of the hoof.
RVC research has examined the biological and physical processes involved in hoof formation through a combination of mathematical analysis, physics and histological examination of hoof tissue.
The findings demonstrated how the hoof capsule develops from the coronet, where soft papillae gradually transition into hard, keratinised tissue.
The research also helped explain how the hoof can grow at a rate exceeding the potential proliferation rate of epithelial cells. In addition, it demonstrated how differences in growth rates across the hoof can produce a curved growth pattern rather than a straight one.
In particular, faster growth from the coronary band towards the quarters, compared with the toe region, contributes to this variation in hoof shape.
Current Laminitis Research At The Royal Veterinary College
The RVC has three ongoing research projects focused on improving understanding of laminitis, its associated risk factors and potential approaches to prevention.
A Long-Term Study Following 250 Ponies
The first project is a long-term cohort study involving 250 ponies that have never previously experienced laminitis.
The animals are visited every six months over a four-year period. During each visit, researchers collect information relating to their physical characteristics, metabolic health and management.
At the conclusion of the study, ponies that have developed laminitis for the first time will be compared with those that have remained unaffected.
The purpose is to identify differences between the two groups and establish which characteristics and factors may be associated with the development of laminitis.
Understanding Horse Carers' Awareness Of Laminitis Prevention
The second project examines how well horse carers understand evidence-based recommendations for preventing laminitis.
Researchers are investigating the factors that encourage or prevent people from adopting management practices supported by scientific research. The study also considers the difficulties horse carers may experience when implementing recommended approaches to prevention.
An online survey was completed by 1,414 respondents. Questions covered a range of subjects, including where people obtain information about lameness, weight management and grazing, their views on scientific research and whether they are able to implement management practices known to reduce laminitis risk.
The survey results are currently being analysed. The next stage involves interviewing a selected group of respondents to explore these findings in greater depth.
Participants will include different types of horse carers, including horse owners, farriers and equine veterinary professionals.
Investigating The Role Of Adiponectin In Laminitis
The third project is investigating the role of adiponectin in endocrinopathic laminitis.
Researchers are examining whether adiponectin receptors are present within the equine lamellae, the tissues involved in supporting the hoof. They are also investigating potential interactions between adiponectin, insulin and insulin-like growth factor-1 signalling pathways.
Another part of the research will investigate how elevated insulin concentrations, the development of tissue insulin resistance and weight gain associated with pasture grazing influence circulating adiponectin levels.
The project will also examine whether approaches used to increase adiponectin concentrations in human metabolic syndrome could have potential applications in equine metabolic syndrome.
In human metabolic syndrome, dietary changes and pharmacological treatments are used to increase circulating adiponectin concentrations and reduce associated cardiovascular disease risk.
The equine research will evaluate the effects of weight loss, both with and without dietary supplementation, on circulating adiponectin concentrations. Potential pharmacological treatments will also be screened in laboratory studies to assess their effects on adiponectin production by adipose cells.
The Continuing Importance Of Equine Laminitis Research
Research undertaken at the Royal Veterinary College has contributed to a broader understanding of equine laminitis, particularly its relationship with insulin dysregulation, equine metabolic syndrome and pituitary pars intermedia dysfunction. Investigations have examined metabolic health, inflammation, obesity, treatment outcomes, diagnostic testing and the biological processes involved in hoof growth.
The current research programme continues to investigate the factors associated with developing laminitis, the effectiveness of preventative management practices and the potential role of adiponectin in metabolic health. Through these studies, researchers are working to improve understanding of the condition and identify factors that may help reduce its occurrence.
Equine laminitis remains an important area of veterinary research, with continued investigations exploring the relationship between metabolic health, management and the development of this painful condition.
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