Chris Bates M.Ost, DipAO, EEBW, BHSAI
Let’s take a look at an often misunderstood condition affecting many horses worldwide, Equine Metabolic Syndrome or “EMS”. For horse owners, and the professionals who care for and treat horses, understanding conditions such as EMS can enhance the horse’s welfare by ensuring that appropriate interventions are put into place.
It should be noted that Veterinary assessment and treatment/management of EMS is vital and that other paraprofessionals should not be working independently of the attending Vet in the management of the affected horses. Always seek Veterinary advice for any of the symptoms described here.
The development of some conditions and their increased prevalence can be impacted by the modern living conditions of animals. While the conscientious owner may be eager to supply their horse with all their needs, some conditions may be exacerbated by the daily routines, feeding regime and physical activity (or lack thereof).
It is essential to remember that the domesticated horse lives in a very different way to their wild counterparts, even when kept in more naturalistic environments with access to varied foraging (Coleby, 2013).
The development of the equine industry has led to a more “processed” lifestyle with all the hallmarks of human modern living issues such as:
- Processed foods
- Daily routines interrupting natural rhythms
- Reduced movement and activity
- Altered socialisation
- Potentially increased stress
- Somatovisceral health impacts
While the longevity of horses and the treatments for life-threatening conditions certainly has improved, the factors affecting overall welfare and evolutionary health have been altered beyond what some equine systems can manage.
It would be naive to assume that these are the only factors in the development of metabolic conditions such as EMS as there is a paucity of studies in relation to horse feed processing for example, compared to in farming livestock (Hill, 2007).
What is Equine Metabolic Syndrome?
As the name suggests, EMS is a “syndrome” meaning it is essentially a combination of signs and symptoms that consistently occur together. This may seem vague in its explanation of what is happening in the individual and can make owners frustrated in their endeavours to manage their horses effectively. This being the case, some horses may not present all of the most obvious signs but still be affected.
EMS could be likened to Type 2 Diabetes in Humans, in that much of the symptomology is mirrored. Signs and symptoms include:
- Obesity - Both generalised or regional adiposity (Alone does not mean EMS)
- Insulin resistance - Basal Hyperinsulinemia or Insulin dysregulation
- Laminitis or a predisposition of laminitis - Without other causes such as inflammatory, infectious, or fracture.
Insulin resistance and either laminitis or a predisposition for it must be present for the EMS diagnosis (Morgan, Keen and McGowan, 2015).
Due to the difficulty in case definition, there is a lack of epidemiological data on EMS prevalence. In the domesticated population of horses, obesity is a concern with up to between 19% and 40% being affected (Morgan, Keen and McGowan, 2015).
Of course, obesity alone is not a definitive sign as discussed above but it poses a high-risk factor in the development of insulin resistance and the resulting laminitic issues. This would indicate that there is a high prevalence for at risk individuals and that could potentially lead to higher case diagnosis if future studies are made.
Equine Obesity and EMS
Horses becoming overweight and obese is a rising concern and prevalence is already high. According to Stephenson, Green and Freeman (2011), many owners may be underestimating their horse's body composition.
This would necessitate better public awareness and education in the health of their animals. Of course, exercise and activity levels are a crucial factor in the management of weight. There are more horses now being kept as companions and non athlete use (Rendle et al., 2018) meaning that this could add to the increased prevalence.
While excess body fat can cause a number of functional problems in general, there is evidence within human studies that elevated levels of inflammatory cytokines such as tumor necrosis factor, IL1 and IL6 can play a role in the insulin resistance in obese individuals (Vick et al., 2007).
As in humans, obesity can be a direct result of inactivity (underactive lifestyle), poor diet and stress. Once a horse has reached a state of obesity, it can become uncomfortable to move effectively and impact negatively on the joints, feet and suspensory apparatus.
Excess body fat can reduce effective respiratory mechanics and lead to postural changes that create ongoing problems. It is easy to see how obesity in horses (or any animal) is a causative factor for a multitude of problems.
Owners in general only mean well in their care efforts and are often just misguided or confused. Horses living healthily have very different requirements to humans and it can sometimes be anthropomorphism that guides an owner’s decisions on care and feeding.
It is not uncommon to find owners over rugging horses because they themselves feel cold or feeding a certain treat or concentrate because they feel the horse “likes it”. The nature of horses' ability to regulate their temperature is often underestimated as is the importance of understanding their nutritional needs.
The activity levels of a horse will depend upon the amount of owner-led exercise they receive (riding, driving, groundwork) and their access to grazing land. Horses that are stabled for longer periods of time consequently require a higher proportion of time spent in guided exercise.
Horses will engage in natural exercise given enough space to do so and this is even more apparent in those with adequate grazing companions as social activity often involves movement. As horses have evolved to be continually moving throughout their waking hours, restricting their ability to do so will impact their wellbeing over all and substitutions need to be made where necessary to support health.
Insulin resistance In Horses
Insulin is an endocrine hormone secreted by the pancreas and it regulates blood glucose levels by acting on the insulin receptors on cell membranes. These insulin receptors, when bonded with insulin, allow for glucose to enter the cell to either be used for energy production or stored as glycogen for later use.
There can be a number of causes to cells becoming insulin resistant. As mentioned earlier, elevated inflammatory cytokines (cellular signalers) can lead to insulin resistance, increased fat intake can also lead to this.
Whichever pathway the body has come to be resistant to insulin, it is usually some kind of disruption to the insulin receptor or the chain of enzyme activation within the cell that the receptor stimulates.
Once the cells have become insulin resistant, the amount of insulin needed to get glucose into the cells will be higher, while the processing of blood glucose becomes less. It is at this point that systemic signs and symptoms of EMS may become apparent. These could include:
- Increased thirst
- Increased urination
- Lethargy
- Muscle atrophy
- Increased hunger
- Frequent infections
- Increased sweating
- Infertility in mares
Laminitis and EMS
This often debilitating condition causes severe lameness and in the most far progressed cases can lead to euthanasia. The epidemiology of laminitis is still poorly understood (Wylie et al., 2011), however, it is clear that there are multiple factors that can lead to the condition including: endocrine, metabolic, traumatic and genetic.
The clinical signs and symptoms include:
- Stiff or shortened stride
- Reluctance to walk on hard surfaces
- Increased digital pulse
- Weight shifting
- Warm or hot hooves
And in the more severe cases:
- Hoof wall changes
- Gapping of the hoof wall to the sole (white line)
- Laying down more often
- Hoof bruising visible
- Laminitic stance - Leaning back onto hind quarters in an effort to alleviate pressure on the forefeet
The laminae are protrusions of tissue that connect the hoof wall to the pedal bone and surrounding cartilages. They are an interwoven mix of the sensitive dermal fibers and the non-sensitive epidermal fibers. These fibers do have a shock absorbing function but when damaged will lose this ability. Traumatic laminitis can occur from impact damage or poor foot dynamics.
In EMS, the enzymes responsible for laminae remodelling are found in higher concentrations. These metalloproteinase enzymes (MMP-2 and MMP-9) are responsible for the normal remodelling of the laminae tissue to allow for growth of the hoof wall.
In higher concentrations, they lead to over active breakdown of the lamellar basal cells attachment to the basal membrane connective tissue of the distal phalanx (pedal bone) (Pollitt, 2004).
The breakdown of the connections between the hoof wall and the pedal bone then obviously allow for the bone to move and rotate within the hoof capsule. With the tensegrity structure of the laminae compromised, functions such as support, shock absorption and hoof wall development are all affected while pain receptors are stimulated.
Evidence seems to suggest that excess adiposity (obesity) leads to an increase in inflammatory cytokines (Ferrante, 2007). Obesity is linked to the increased number and activation of macrophages in adipose tissue further increasing the inflammatory cascades.
Adipose tissue expression of genes that encode for a number of inflammatory cytokines includes the metalloproteinases mentioned earlier. From a structural perspective, it is also worth mentioning that increased weight of the body will then further impact the weakened structures of the distal limb including the laminae that are damaged.
Feeding and its EMS Connection
When we prepare food for ourselves, it can be part of the process to consider what we enjoy eating and what tastes good. Unfortunately, as we see from the rising figures of obesity, diabetes and heart disease, it is not actually always doing us much good from a health perspective.
There are of course many evolutionary reasons why humans so easily fall into the habit of craving certain foods and choosing foods that provide energy storage; however, horses as grazing animals have very different dietary needs and evolutionary development.
Horses certainly can enjoy particular types of food but it is the human providing them that decides the quantity of food they receive. In the wild, a herd may come across a particular forage that is very palatable and easy to access but once the herd (important to remember multiple animals) has eaten it, they will move on and balance of intake is achieved (Frape, 2010).
When we feed in domesticated horse care, we must remember this variation of supply they would naturally be faced with. This should remind us to vary the concentrates and type of forage depending on their current health, weight, the time of year and their exercise demands.
Ratios of protein, carbohydrates, fibre and fats should be monitored depending on the above variables (Harris and Jansson, 2024). If owners fall into the habit of keeping a feed regime the same without adjusting for the variables, obesity can be one of the results.
Exercise and activity
Horses are movement machines and evolved to roam across large open spaces while grazing along the way. Their access to large open space will depend on where they are kept and what the quality of the land is like.
Some more competitive horses may be stabled more often as may some horses with health conditions and injuries that limit their movement capacity (Marlin and Nankervis, 2006). The most important principle to remember when caring for an EMS horse or trying to prevent it occurring, is that movement is medicine.
To ensure that the energy demand is sufficient so that excess fat storage does not occur is just one goal of equine exercise. Movement does not have to be excessive either. Much of the time wild equines spend “exercising” is simply walking from one region of grazing to another.
This longer sustained form of lower intensity exercise is often key in the management of excess weight gain. This lower intensity/longer duration exercise can be achieved with hacking out at walk and trot, longer schooling sessions focussing on the walk figures and even hand walking for horses who may not have sufficient health status or age to be riding.
Higher intensity exercise is usually reserved for horses that are sports competitors, working horses or have a special health requirement such as losing excess weight already gained. These should be planned and logged even informally to allow for the owner/rider/trainer to monitor progress and assess fitness levels.
While higher intensity exercise is very effective at weight management, it does increase the risk of injury, overuse strains, loss of vital electrolytes via sweating and can even lead to serious conditions like rhabdomyolysis (muscle breakdown).
The plan for increased intensity should consider the horses other health conditions, age and training level. It is essential for all exercise changes to be graduated and progressive so as to allow for physiological changes to occur and support the healthy functioning of the body.
Diagnosis and Treatment of Equine Metabolic Syndrome
I have touched on many of the symptoms of EMS above. Here is a compiled list of symptoms that indicate you should consider consulting with your equine veterinarian to evaluate if your horse has EMS
- Obesity, which can include a crusty neck, abnormal fat deposits and bulges
- Increased urination
- Increased thirst
- Lack of energy
- Low grade, sometimes unnoticed laminitis to more severe cases
- Struggling with weight loss
- Mare infertility
While owners can suspect their horse has EMS, diagnosis can only be made by a veterinarian. One of the main ways this is done is by blood tests taken at specific times, such as first thing in the morning before feeding to check insulin levels before it is affected by food.
According to the UC Davis Veterinary Medicine Center For Equine Health, “If the insulin concentration is above a certain level (>50 µU/mL), the horse is diagnosed with insulin dysregulation.” Other tests may also be carried out to further determine the horse’s status.
Treatments include changes to diet, such as low non-structural carbohydrate consumption, restricted grazing, and increased exercise (if the horse is capable), feed and hay analysis (UC Davis)
Conclusion
EMS is a condition that has the potential to grow if owner education is poor and incorrect feeding and exercise/movement regimes are used. In our future posts, I will discuss equine nutrition and fitness in more detail.
It is evident that excess body fat is a key factor in development of EMS and it is widely known that obesity is a risk factor for other health concerns too. The inflammatory effects of obesity are well documented, with inflammation being well researched in human models, it would advance equine science and care to invest more into the longer term effects of chronic inflammation in horses.
Learn more in depth detail of the pathologies that affect horses and how Osteopathy works to support better health by signing up to one of our diplomas. The London College of Animal Osteopathy provides quality education in animal health whether you are an aspiring professional, experienced practitioner or just want to improve your knowledge.
Bibliography:
Coleby, P. (2013). Natural Horse Care : a practical guide. Sydney: Hachette Australia.
Ferrante, A.W. (2007). Obesity-induced inflammation: a metabolic dialogue in the language of inflammation. Journal of Internal Medicine, 262(4), pp.408–414. doi:https://doi.org/10.1111/j.1365-2796.2007.01852.x.
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Frape, D. (2010). Equine nutrition and feeding. Uk: Wiley-Blackwell.
Harris, P.A. and Jansson, A. (2024). Nutrition for the Equine Athlete: Nutrient Requirements and Key Principles in Ration Design. Elsevier eBooks, [online] pp.925–953. doi:https://doi.org/10.1016/b978-0-7020-8370-9.00041-2.
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Marlin, D. and Nankervis, K.J. (2006). Equine exercise physiology. Oxford: Blackwell Science.
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