How Big is the Equine Obesity Problem in the UK and what Advice Can Be Given?

Prevalence of equine obesity in the UK

Equine obesity in the UK is as high as 70% in some populations [1]. However, measuring prevalence is difficult as it varies with factors such as time of year and who is reporting (owner vs. vet). Human behaviour has a significant impact, as with obesity in other species, where excessive fat tissue has increasingly become the norm [2]. In the biggest study to date, owners reported a prevalence of 31.5% [3], which is likely to be an underestimate given the reported poor owner recognition. Owners seem to find it particularly difficult to recognise obesity in native ponies and cobs, probably because they are already a bigger, rounder shape [4]. Robin et al. found that breed, being described as a ‘good doer’, and being a leisure horse were the highest risk factors for obesity, while ponies have been shown to have a prevalence as high as 72% [5].

Obesity, hyperinsulinaemia and laminitis

Obesity is a risk factor for insulin dysregulation. The exact mechanism is complex, but a convenient analogy when discussing with owners is that adipose tissue behaves like an ‘endocrine organ’, secreting proinflammatory mediators, hormones and other cytokines that are harmful to the body. Hyperinsulinaemia is associated with increased risk of laminitis, the degree of which has been shown to be predictive. A 4-year prospective cohort study found that low basal insulin (<21.6) levels were associated with a 6% incidence, moderately elevated insulin (21.6–45.2) with 22%, and high insulin with 69% incidence of laminitis [6]. 90% of laminitis cases are endocrinopathic, as opposed to inflammatory or mechanical [7], with the cause of hyperinsulinaemia being mostly obesity and/or pituitary pars intermedia dysfunction (PPID).

Obesity and equine metabolic syndrome

Obesity is a common feature in horses with equine metabolic syndrome (EMS) – a complex of metabolic abnormalities, which includes insulin dysregulation, and often presents with laminitis. EMS has a prevalence of 23% in natives and cobs and, alongside obesity, other risk factors are age, being female, sedentary activity, and shorter periods on pasture during the summer [6].

Laminitis risk factors, diagnosis and mortality

Risk factors for laminitis include native breeds, ponies over horses [8] and being used for leisure. Turnout at grass has been associated with increased risk [3], and two other studies showed that short periods of turnout could also be problematic [6,9]. Studies have shown that 1 in 10 horses will suffer from laminitis at some point in their lives [6,9]. In addition to this, 45% of cases are not detected by owners [9]. Carslake et al. found only 50% of laminitis cases were presented to a vet. Owners most commonly noticed difficulty turning and lameness, but missed factors such as growth rings or unusual presentations [9,10]. Laminitis has been reported as the most common reason for euthanasia in a cohort study of 1070 horses, accounting for 25%, closely followed by colic, 21% [11].

How can vets help reduce obesity in their daily work?

• Address cases on welfare grounds.
• Confident assessment/quantification of obesity.
• Improved communication with owners.
• Educate owners about predisposition, obesogenic factors and recognition.
• Understand endocrine tests, e.g. insulin, glucose, ACTH.
• Understand medication, e.g. sodium-glucose co-transporter 2 inhibitor (e.g. velagliflozin), metformin, levothyroxine.
• Offer tailored, achievable advice on management [1], e.g.:
  • Low calorie balancer only (no chaff or other ‘hard feed’).
  • 1.5–2% bwt dry hay/24hr, soaked, mixed with straw (70:30 hay:straw), trickle-feeding, low-sugar haylage.
  • Grass restriction e.g. no grass, strip-grazing, track system, grazing muzzle.
  • Increased exercise e.g. frequency, distance, duration, intensity, additional rider, horse-walker. o Increase heat loss e.g. rugging, clipping.

What is the equine industry doing to tackle obesity?

In 2017 BEVA started the Obesity Working Group, which has carried out pilot projects to try to better understand the challenges vets face in the field, with a focus on human behaviour change. Then in 2020, the British Horse Council started the Equine Obesity Roundtable initiative, bringing together a number of equine charities, the British Horse Society and BEVA, with the ‘long game’ in mind. The issue is complex, multifactorial and going to require a committed and co-ordinated approach.

[...]