As the horse's role has shifted from work animal to leisure and companion animal, overweight has become one of the most common health problems in the domesticated population.
As the horse's role has shifted from work animal to leisure and companion animal, overweight has become one of the most common health problems in the domesticated population. A review of the research puts the prevalence of overweight at between 19 and 40 per cent in domesticated populations, while a European consensus report paints a similar picture: prevalence in different horse populations ranges from 21 to 45 per cent in the United Kingdom, with lower figures in some other countries – for example 10 per cent in adult Icelandic horses in Denmark.
Equine metabolic syndrome (EMS) describes a cluster of clinical abnormalities. Research defines it as insulin resistance, generalised obesity and/or increased fat deposition at specific sites on the body, associated with a raised risk of laminitis. The core problem is what researchers call insulin dysregulation: basal or postprandial hyperinsulinaemia and tissue insulin resistance, which in turn raises the risk of the most serious consequence – laminitis.
The link between insulin levels and laminitis is well established experimentally. Research has shown that sustained hyperinsulinaemia experimentally induces laminitis in healthy ponies and horses, which establishes a causal relationship.
Laminitis is one of the most serious and most painful conditions a horse can suffer. Research shows that more than 90 per cent of horses presented for veterinary care with laminitis as the primary clinical sign have developed the condition as a consequence of endocrine disease, most often equine metabolic syndrome.
Who is affected? An important nuance is that overweight is not a prerequisite: research notes that although overweight is a common finding, EMS can occur in lean animals, and not all overweight horses are affected – which makes objective diagnostic testing necessary rather than relying on body-condition scoring alone.
Some breeds are particularly susceptible. Research points out that certain types such as Shetland ponies, donkeys and miniature horses are often exercised less than many other breeds as part of standard care, which can add to the raised risk. The same research notes that horses with EMS are often described as 'easy keepers' or 'good doers', and that the genes behind this phenotype were likely an advantage for survival in the wild during periods of scarcity, by improving the use of feed – an evolutionary background that now becomes a welfare risk in an environment rich in feed.
Treatment rests first on a change of lifestyle rather than on medicines. Research emphasises that management is centred on strict restriction of rapidly digestible carbohydrate in the diet, controlled forage intake and the elimination or careful management of grazing, and that regular exercise improves insulin sensitivity but must be adapted to the horse's laminitis status, and that appropriate hoof care is essential given the high incidence of chronic and recurrent laminitis.
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A cluster of insulin resistance, obesity and raised risk of laminitis – the core is insulin dysregulation.
No – EMS can occur in lean individuals, and not all overweight horses are affected. Objective diagnosis is needed.
Primarily through diet (restricted rapidly available carbohydrate), controlled forage, adapted grazing and regular movement, together with hoof care.