In the first part of this two part blog, we discussed the impact of hormones and the endocrine system which includes the pituitary gland and hypothalamus in the brain, as well as the adrenal glands. Alongside producing hormones that are crucial to growth and development, the endocrine system also exhibits a pivotal role within your horse’s metabolism.

However, sometimes this intricate system doesn’t function as well as it should. In this blog, Lisa Elliott, MSc – Equine Nutrition Solutions investigates the reasons why this happens and the impact on your horse’s health and well-being.

Endocrine system diseases can develop when too much or not enough hormones are produced, or when normal pathways for hormones to be used and removed are disrupted. There are two main endocrine diseases commonly found in horses: Equine Metabolic Syndrome (EMS) and Pituitary Pars Intermedia Dysfunction (PPID), also known as Equine Cushing’s Disease. Both conditions can lead to laminitis, which represents a significant impact on a horse’s health, but they have distinct differences.

Equine Metabolic Syndrome (EMS)

Horses that are good doers and gain weight easily can sometimes be more prone to EMS. This is because EMS is often associated with rising levels of obesity in horses, though not all obese animals have EMS, and this condition can still occur in horses and ponies of normal weight. However, even if a horse’s history is unknown, and they are currently at a normal weight and have EMS, it’s likely they were obese at some point. Ponies, especially native breeds, were traditionally thought to be more susceptible to EMS and weight gain, but it’s important to recognise that any horse can develop the condition.

In animals prone to EMS, fat tends to accumulate at the crest, around the shoulders, and across the rump and buttocks, with significant internal fat as well. They start to lay down fat pads filled with abnormal fat cells which release various hormones and factors into the blood stream. These hormones will have profound effects on a horse’s metabolism which leads to what is known as Insulin Dysregulation (ID) and will result in ‘insulin resistance’.

Insulin Resistance and laminitis

When a horse consumes simple sugars like glucose and sucrose, insulin is released from the pancreas which stimulates the movement of these sugars from the blood into the cells. However, a horse or pony with insulin dysregulation loses their sensitivity to insulin and, therefore, becomes insulin ‘resistant’. This causes the production of more and more insulin in a bid to shift the sugar into cells, which results in a state of Hyperinsulinemia (defined as the circulation of inappropriately high concentrations of insulin) and significant potential for laminitis.

While the direct mechanism is not fully understood, it is thought that higher levels of insulin circulating within the blood (Hyperinsulinemia) can result in disruption to blood flow within the hoof which directly results in laminitis – a painful and distressing condition for horses and ponies. Treatment involves addressing both the laminitis and the underlying EMS through the right diet and management approaches.

Equine Cushing’s Disease/PPID

Equine Cushing’s Disease, also known as Pituitary Pars Intermedia Dysfunction (PPID), results from the loss of specific nerve cells, leading to hormone disturbances due to the overdevelopment of the pituitary gland in the brain, and consequently, excessive production of the hormone ACTH (Adrenocorticotropic hormone) and a few other hormones. This condition is very common in older horses, affecting around 85% of senior animals, though it is increasingly diagnosed in younger horses. The main clinical signs include.

• Lethargy
• Poor performance
• Muscle loss
• Sweating
• Curly coat
• Pot belly appearance
• Pottery gait
• Severe or recurring laminitis
• Recurrent infections (due to decreased immunity)

The enlargement of the pituitary gland is usually slow and often shows no clinical signs. However, in very rare cases, it can be associated with neurological signs such as behavioural changes, seizures, or blindness.

PPID, like EMS, will invariably lead to laminitis but the exact link between PPID and Laminitis is not fully understood and research into this area is ongoing. One theory is that horses with this condition seem to show an exaggerated insulin response (high insulin levels in blood) to food containing sugar (glucose). This means that when a horse eats high sugar grass, they will develop high levels of insulin in their blood, and the resulting hyperinsulinemia will cause laminitis.  

It is also thought that the overproduction of cortisol in horses with PPID (due to high levels of ACTH), disrupts normal insulin regulation which may then lead to insulin resistance.  However, all of this is further complicated by the fact that not all horses with PPID will have insulin resistance, and not all horses with insulin resistance will have PPID. Additionally, some horses with PPID can also have EMS which means they are more likely to have the associated insulin dysregulation (ID) anyway. Generally, for a horse or pony with PPID to get laminitis they also need to have ID.

The good news is PPID can be easily diagnosed through a blood test measuring ACTH level, either at rest or after stimulation. If the test results are positive, there are treatment options available which can be used alongside good management to ensure optimum quality of life.

Managing EMS and PPID

Whilst there is no ‘cure’ as such for EMS or PPID, there are a range of good management and preventative options to help mitigate the effects and help horses and ponies with either or both conditions, live a happy and healthy life.  In theory, EMS, in particular, can be ‘reversible’ with intense management.

Weight loss

If your horse is overweight then taking steps to reduce this and get them to a healthy weight, is fundamental in the management of EMS, and horses with PPID who are also overweight. There are many weight loss strategies that can be used, involving reduction of calorie intake but without compromising on fibre intake, and also strategic rugging in winter to help horses lose weight naturally as they should do during winter to prevent rapid weight gain in the spring.

Regularly using Body Condition Scoring and Weight tapes to help get your horse to a target weight and assess if the weight loss plan is working is also essential.  Ensuring all horses or ponies are maintained at a healthy weight throughout the year is also an excellent prevention tool for the development of obesity and EMS in the first place.

Exercise

Exercise is one of the best things you can do for EMS and PPID, once your horse or pony is able to, but it should be built up gradually, partially if your horse is recovering from associated laminitis.  

Exercise helps to

• Burn fat
• Boost metabolism
• Improve the uptake of glucose by muscles
• Reduce blood sugar levels
• Increase insulin sensitivity

These are all absolutely invaluable for mitigating the effects of both EMS and PPID. For optimum results, exercise needs to be regular and fairly intense (once fitness has been gradually built up) including hill or canter work as long as your horse or pony is able to. 

Diet

The right nutrition is also key in the management of both conditions and the prevention of laminitis.

• Starch and sugar levels need to be kept low. Ideally they should be less than 10% of the whole diet – not just their daily feeds
• Soaking and/or steaming hay to reduce starch, sugar, and calorie content (if the horse is overweight)
• Restricted turnout at certain times of the day when grass sugars are lower
• Strip grazing can help lower the overall starch and sugar content in the diet

If your horse needs extra calories for work or condition, avoid cereals and provide additional calories through sources of digestible fibre and oil which are lower in starch and sugar.

All of the Coligone Range is low in starch, sugar, and calories and higher in digestible fibre and can be used to provide optimum nutrition for horses and ponies with EMS or PPID as part of a support and management plan.