Insulin dysregulation and ponies: It’s not always in the eye of the beholder
A study by researchers at the Royal Veterinary College in Britain has found that insulin dysregulation status in ponies cannot be determined solely by observation of body condition.
The results highlight that insulin dysregulation (ID), and the associated increased risk of laminitis, may occur in ponies across a wide range of body conditions, ages and levels of exercise, not just in those that are overweight. The study also showed that ID was less common in ponies that undertook more exercise including low-intensity exercise.
In the study carried out by Edd Knowles and colleagues at the Royal Veterinary College, London, researchers carried out 1763 oral sugar tests from 367 non-laminitic ponies over four years. The study was conducted in collaboration with the makers of Spillers horse feed, via the Waltham Equine Studies Group.
Sarah Nelson, Product Manager at Mars Horsecare, home of the Spillers brand, said the work confirms that while body condition is a useful indicator, it can’t be assumed that ponies with obvious physically apparent attributes such as excess weight are the only group likely to have ID.
“We must consider multiple variables when targeting ponies for ID screening, in order not to miss those potentially at increased risk of laminitis, who may have a ‘healthy’ body condition score. The association with even low-level exercise is also an important practical management message for horse owners,” Nelson said.
Insulin is a hormone produced by the pancreas. The release of insulin is the signal for cells, largely in muscle and liver tissue to absorb glucose (sugar) from the blood. Insulin dysregulation (ID) is a term that includes a high basal or ‘resting’ insulin (in the blood), an exaggerated insulin response to consuming starch and/or sugar and tissue insulin resistance (a failure of cells to respond to insulin).
The concentration of insulin was measured in the blood of ponies in this study before and sixty minutes after they were given, orally, a sugar syrup (an oral sugar test (OST)). An association between ID and laminitis is well-established and early detection of ID is likely to be useful in helping to prevent the disease.
Over the four years of the study, the ponies were visited and tested in the Spring and Autumn unless they developed laminitis. Various physical parameters were recorded at the time of each OST including weight, height, body length, neck length, heart girth, belly girth, body condition score and cresty neck score. Owners/carers were asked to complete a questionnaire concerning the specific characteristics, diet, management, duration and intensity of exercise and health for each pony at each visit. Serum insulin concentration at 60 min (InsulinT60) during an OST, in the first paper from this work1 has been shown to be an indicator of future laminitis risk.
The study concluded that associations between InsulinT60 and physical and owner-reported variables were limited; Season, owner-reported and physical features only explained 10% to 27% of the differences in InsulinT60 risk status in the study population.
The findings support previous work that suggested body condition scoring alone was not sufficient to determine insulin dysregulation (ID) status and emphasises the value of using an oral sugar test to screen for ID status.2
Lead author Edd Knowles said: “Our work has shown that while physical and owner-reported features can be used to identify ponies with a higher risk of ID, veterinarians should not limit testing for ID to ponies in which these risk factors are present. Doing so would miss identifying ponies at moderate to high risk of laminitis.”
The study also indicates that relatively small increments in equine exercise routines may be beneficial. 18% of samples from ponies that were reported to do no trotting exercise were in the high-risk InsulinT60 category compared with only 9% of samples from those reported to undertake one to two hours of trotting per week. This finding supports earlier research on the benefits of low-intensity exercise.3
“We are proud to be involved with this important work which brings considerable practical information to horse owners,” Nelson said. “As our understanding of the diagnosis and management of insulin dysregulation develops, we will become better equipped at helping to prevent laminitis, with the ultimate goal of eradicating this debilitating disease altogether.”
Factors associated with insulin responses to oral sugars in a mixed-breed cohort of ponies. Knowles EJ, Harris PA, Elliott J, Chang Y-M, Menzies-Gow NJ. Equine Vet J. 2023. https://doi.org/10.1111/evj.13983
1. Knowles, E.J., Elliott, J., Harris, P.A. Chang, Y.M. and Menzies-Gow, N.J. Predictors of laminitis development in a cohort of non-laminitic ponies. Equine Vet. J. 2023: 55 (1) 12-23
2. N.R. Liburt, S.L. Mastellar, E.R. Share, P.A. Harris. How challenging is it to find non-insulin dysregulated horses in an apparently clinically healthy herd of university horses? Journal of Equine Veterinary Science. 2023; 124. https://doi.org/10.1016/j.jevs.2023.104389.
3. Bamford, N; Potter, S; Baskerville, C; Harris, P; Bailey, S. Influence of dietary restriction and low-intensity exercise on weight loss and insulin sensitivity in obese equids J Vet Intern Med. 2019. 33:280- 286
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