Equine metabolic syndrome in UK native ponies and cobs is highly prevalent with modifiable risk factors.
Equine Vet J. Sept 2021 53:923-934. Published online 30 Oct 2020. doi: 10.1111/evj.13378.
Keywords: EMS; epidemiology; horse; laminitis; obesity; prevalence
This paper is discussed by Harry Carslake in the February 2021 EVJ podcast:
EVJ In Conversation Podcast No. 48, February 2021 - Equine metabolic syndrome and Wound management in the horse.
EMS is a collection of risk factors for endocrinopathic laminitis, of which the most important is insulin dysregulation (ID).
ID = increased circulating concentrations of insulin, either at rest or in response to a meal, and/or insulin resistance in the cells (when the cells don't respond to insulin in the normal way).
The most important clinical manifestation of EMS is laminitis - a horse with EMS has an increased risk of getting laminitis (due to insulin dysregulation).
We commonly think of a horse with laminitis having obvious pain in both front feet, but laminitis can be much more subtle (see later - hoof rings).
EMS can also involve obesity and abnormal metabolic behaviour of fat.
EMS is a combination of a genetic predisposition [i.e. hardy/native breed] and management/environmental factors. In theory any horse could get EMS and therefore endocrindopathic laminitis, but some horses are much more susceptible than others. For example, a Standardbred which genetically is likely to have a low risk of EMS, given certain management [e.g. being overweight, a high sugar/starch diet and/or insufficient exercise - also corticosteroid use] can still get EMS and laminitis.
Diagnosis - look at risk factors in management, e.g. if a horse is fed a high concentrate/NSC diet, clinical examination, breed. To confirm the diagnosis, test for ID. Basal - after fasting or feed, or dynamic - give known amount of glucose and look at insulin response. The dynamic oral tests are the most useful - convenient, and probably similar to situation that causes laminitis, and takes into account communication between gut and pancreas in response to a meal. [NB resting (basal) insulin is generally not a good test for ID].
The study aimed to estimate the prevalence of EMS in a population of horses and identify and quantify risk factors. Horses identified as being likely to have EMS could then have dynamic testing to diagnose EMS, and therefore increased risk of laminitis. If blood testing wasn't not an option (e.g. if owners didn't want to pay for testing), EMS could be presumed and management of EMS implemented. Modifiable risk factors can be used to help with management of EMS [diet, weight loss, exercise].
The population sampled was within 75 km of Leahurst, aged 3-14), native ponies/crosses and cobs. 354 horses on 64 properties were included. They excluded horses with PPID - horses aged over 10 had a basal ACTH to rule out PPID, lactating mares, mares in third trimester of pregnancy (this causes increased insulin resistance), horses with obvious laminitic foot pain, horses on medication that could influence insulin sensitivity e.g. corticosteroids, metformin.
The horses were stabled the night before their assessment with 1 slice of hay (so effectively fasted for 5-6 hours). The assessors arrived around 8 am and took blood to test basal glucose, insulin (and in horses over 10) ACTH. Then the horses were given 1g/kg glucose in a known amount of low glycemic chaff, and blood taken 120 minutes later to test glucose & insulin. The horses were given a clinical exam: body condition score, cresty neck score, hoof score. The owner/keeper was interviewed about management, exercise, feed, medical history.
It was a one-off visit - the research did not follow up cases. 23% of the horses were diagnosed with EMS (the diagnosis was based on cut offs in the current EMS consensus statement). Welsh As had the highest prevalence of EMS compared to Welsh B, C, D, cobs & Connemaras. Other studies have found an inverse relationship between the height of a horse and its insulin sensitivity, i.e. smaller horses are more likely to have EMS. EMS was associated with increased age, breed and higher post-prandial insulin concentrations. Mares in this population had increased risk (even when mares in their first trimester of pregnancy were excluded). Horses with a less active main use (stud, showing, companion) were 3.5 times more likely to have EMS than horses that were ridden or driven. Horses with a BCS of 7+ were 3 times more likely to have EMS. Horses at grass in the summer for less than 6 hours a day were associated with increased likelihood of EMS, as were horses that weren't rugged in winter. However, remember that association isn't the same as causation! Owners of horses known to have an increased risk of EMS (e.g. overweight) are likely to turn horses out for less time and not rug. But there may also be possible mechanistic explanations why less turnout and not rugging could increase the risk of EMS, particularly not rugging [because horses not clipped and rugged tend to be worked less??] [there is research suggesting horses at grass all the time have a lower risk of EMS - perhaps more exercise from moving around, less binge eating??].
Horses with a previous episode of laminitis in the last 5 years were 14 times more likely to have EMS [their laminitis was almost certainly caused by ID/EMS]. Knowing that a horse has a history of laminitis is important and should for example be taken into account if considering the use of corticosteroids or how much grazing to allow.
Hooves were scored for the prominence and divergence of hoof rings. Horses with increased prominence and divergence of hoof rings more likely to be EMS positive.
There are good histological studies that show that prominent and divergent hoof rings are associated with sub-clinical laminitis [note this means that laminitis HAS occurred, and x-rays should be taken!].
The message for vets: Early detection of EMS before a horse gets laminitis is important. Once a horse has got laminitis it's very difficult to manage horses [debatable - not with good foot care!]. Use risk factors - breed, increasing age, being overweight, no/reduced exercise, history of laminitis, hoof morphology (prominent & divergent hoof rings) - to guide the implementation of management changes for the horse, and/or blood testing e.g. the oral sugar test (OST). Diet and exercise are the pillars to reduce circulating insulin concentration/ID and therefore EMS.
Take home message - early detection of horses with EMS is so important for horse welfare. EMS is common in ponies and cobs. Risk factors can be used to help detect EMS, and modifiable risk factors can be used to reduce EMS.