Non-laminitic ponies can be reliably classified for their laminitis risk through insulin testing, researchers in Britain report.
Basal serum insulin concentrations and levels following an oral sugar test can each be applied to classify ponies as either being in high, medium or low laminitis risk categories.
Preventative strategies could then be targeted at those at greatest risk, Edward Knowles and his fellow researchers reported in the Equine Veterinary Journal.
Researchers in the Royal Veterinary College study set out to to identify the most useful physical, metabolic, and management factors to predict development of the potentially crippling condition in client-owned non-laminitic ponies.
Equine laminitis can be classified as endocrinopathic, inflammatory or mechanical in origin. The endocrinopathic form is the most common, and ponies are at higher risk than horses.
Endocrinopathic laminitis has been linked with metabolic factors, body size and shape, and management risk factors. However, the relative importance of these different risk factors and precise quantification of risk requires further study, they said.
The authors hypothesised that the development of laminitis would be associated with management, metabolic and physical-examination findings that could be combined into a clinical prediction model.
Overall, 374 ponies, aged 5 to 32 years and housed at 24 premises in southeast England, were followed in the study.
Researchers visited each pony every six months, in spring and autumn, amounting to up to eight visits between 2015 and 2019. At each visit, each pony underwent a standardised veterinary examination. Blood was collected for analysis, physical/clinical measurements were taken, and caregivers filled out a questionnaire.
Each pony was weighed with a portable weighbridge and a modified oral sugar test was performed.
Ponies were syringe-dosed with a light corn syrup at a rate of 0.3 millilitres per kilogram of body weight. Blood samples were taken 30 and 60 minutes later to measure insulin concentrations.
The base blood samples were tested for insulin levels, adiponectin, triglycerides, glucose and adrenocorticotrophic hormone. The animals were not fasted beforehand, but owners were asked not to provide any additional feed on that day.
The samples taken at 30 and 60 minutes were analysed only for insulin.
In all, 891 pony-years were included in the main analysis. Laminitis incidence over the study period was found to be 4.8 cases per 100 pony years.
A total of 43 cases of laminitis were reported among the study population, of which 32 were confirmed by a veterinarian. Of the remaining 11 cases, laminitis was diagnosed by a farrier in eight instances and by the owner/carer (all experienced riding school owners or managers) in three.
A total of 128 ponies left the study group for reasons other than laminitis, of which 33 died or were euthanised, and 70 moved or were sold.
Significant contributors to laminitis risk included a higher body condition score, evidence of divergent hoof growth, the presence of excessive hair growth on veterinary examination, increasing age, higher baseline insulin levels, higher insulin levels 60 minutes after the oral sugar challenge, lower adiponectin, and lower exercise levels and/or intensity.
There were marked seasonal differences in laminitis incidence, with summer rates around three times higher than winter rates.
The final combined models used baseline insulin levels, the level 60 minutes after the sugar challenge, and hoof divergence. All those factors were significantly associated with laminitis.
However, the authors found little additional predictive power was achieved by combining these multiple factors when compared with assessing only a single blood test – in particular, insulin levels 60 minutes after the oral sugar challenge. Baseline insulin levels also proved effective in assessing this risk.
The study team was thus able to categorize ponies into low, medium and high-risk categories for laminitis development based only on their insulin test results. In all, 70% of the study ponies fell in the low-risk category, 20% in the medium-risk group, and 10% in the high-risk group.
In conclusion, the authors said risk appears to be concentrated in a minority of ponies that are best identified by basal or oral-sugar-test-stimulated serum insulin concentrations. The values identified in the study may be used to classify ponies in terms of their laminitis risk.
The study team comprised Knowles, Jonathan Elliott, Yu-Mei Chang and Nicola Menzies-Gow, all with the Royal Veterinary College; and Patricia Harris, with the Waltham Centre for Pet Nutrition.
Knowles, EJ, Elliott, J, Harris, PA, Chang, Y-M, Menzies-Gow, NJ. Predictors of laminitis development in a cohort of nonlaminitic ponies. Equine Vet J. 2022; 00: 1– 12. https://doi.org/10.1111/evj.13572