Equine metabolic syndrome (EMS), a major risk factor for laminitis in horses, is common among Britain’s native ponies and cobs, the findings of fresh research suggest.
The University of Liverpool study provides the first robust prevalence estimate of EMS among susceptible British breeds, based on the results of a test for insulin dysregulation, considered one of the defining features of the syndrome.
The study findings also support the association between higher fat levels and EMS.
Lead author Harry Carslake, who was a lecturer in equine medicine at New Zealand’s Massey University from 2006 to 2011, said obesity, EMS and laminitis have a major impact on equine welfare in many parts of the world.
“There is still a lot we don’t know about them.”
The study by Carslake, Dr Gina Pinchbeck and Professor Catherine McGowan centered on clinical examinations of 354 animals at 64 properties within 75km of the University of Liverpool, covering an area in northwest England and northern Wales.
The properties comprised 19 studs, 19 livery yards and 26 registered riding schools.
The ponies and cobs were all aged 3 to 14. Animals were excluded from the study if they had a previous diagnosis of Cushing’s disease or any other current systemic malady, had received any medication likely to affect insulin levels, or were heavily pregnant or had a foal at foot.
As well as the clinical examination of each pony, which included an insulin test, blood sampling, body condition scoring and cresty neck scoring, the owners were asked a series of questions about their animals in face-to-face interviews.
The overall prevalence of EMS, after a statistical adjustment for clustering within yards, was 23.3%.
Risk factors linked to an EMS diagnosis included age, being female, a more sedentary main activity (such as showing, breeding, or being a companion animal), obesity, and shorter periods on pasture during the summer.
Compared to Welsh section A ponies, the other Welsh, Connemara and cob breeds all had decreased odds of EMS.
The study team, reporting in the Equine Veterinary Journal, said hoof growth rings and higher levels of fat above the eye sockets were more frequent in EMS-affected ponies and cobs.
It was found that 9.7% of the animals in the study had been affected by laminitis within the last five years. These animals were 14.4 times more likely to be positive for EMS than those without such a history.
They noted that the frequency of previous laminitis may be an underestimate, as the median length of ownership of all animals was three years.
The authors described the level of EMS among Britain’s native ponies and cobs as highly prevalent.
“The prevalence of 23.3% demonstrates that a significant proportion of 3 to 14-year-old native ponies and cobs in the UK are at increased risk of developing laminitis,” they wrote.
Mares had greater odds of EMS than geldings and stallions. The authors suggested that the effects of female sex hormones on insulin levels might contribute to this finding.
An absence of winter rugging and decreased turnout at pasture in the summer were two novel risk factors identified in the study that were associated with increased insulin and risk of EMS.
These contradict most current opinion, the authors noted, although they stressed that their study had identified an association and not a cause.
“It is possible that they represent owners identifying animals at increased risk of EMS (due to obesity or previous laminitis) and modifying management according to current advice of keeping horses unrugged to promote cold-induced thermogenesis and restricting summer turn out to reduce grass intake.”
Carslake and his colleagues noted that the significant risk factors identified in the study were modifiable by owners, such as obesity and the level of activity undertaken by the animals.
“Modifying risk factors could help reduce the risk of laminitis in susceptible animals,” they said.
Carslake, who undertook the study as part of his work towards a doctorate, told Horsetalk that although the study population was British ponies, the risk factors identified are likely to be applicable to the same breeds in New Zealand.
Equine metabolic syndrome in UK native ponies and cobs is highly prevalent with modifiable risk factors
H.B. Carslake, G.L. Pinchbeck, C.M. McGowan
Equine Veterinary Journal, October 30, 2020 https://doi.org/10.1111/evj.13378
The study, published under a Creative Commons License, can be read here.