Diabetes mellitus is a metabolic disease in which high levels of glucose are found in the blood and therefore in the urine.
In a normal situation the body's insulin is in charge of regulating glucose levels by moving blood glucose into the tissues where it will be used to produce energy.
When diabetes mellitus is present, it can be due to a lack of production of insulin or a decreased sensitivity of the tissues to it, consequently there will be a failure in the transport of glucose outside the bloodstream. Two types of diabetes mellitus are described:
Diabetes mellitus type I: there is a decreased production of insulin by the cells of the pancreas, so there are low levels of insulin in the blood. This is associated with an immune-mediated cause. It is less common that type-2 diabetes.
Diabetes mellitus type 2: there is not enough production of insulin or the cells become resistant to it. It appears to be more common in humans than type 1 diabetes.
Although diabetes mellitus is uncommon in horses, there is a condition called Equine Metabolic Syndrome (EMS) that has few similarities with diabetes mellitus type 2.
The term EMS in horses defines a group of risk factors for the development of laminitis. Obesity is one risk factor. This can be generalised or focalised in certain areas of the horses bodies like around the base of the tail, over the eyes, behind the shoulders, on the crest of the neck. Other risk factors include being a ‘’good doer’’, difficulty in losing weight and abnormal insulin responses.
Obesity is defined by the World Health Organisation as abnormal or excessive fat accumulation that presents a risk to health. Like in human’s diabetes mellitus, obesity in horses plays a main role in the development of EMS. Fat tissue secrete hormones that have an adverse effect and it seems to be associated with the development of insulin resistance, inflammatory conditions and cardiovascular function.
Similarly to human diabetes mellitus type 2, in horses with EMS we find high insulin level in the blood. Insulin levels can be persistently high or have a high response to food consumption which is called post-prandial hyperinsulinemia. The situation where there is a failure of the tissues to respond to the hormone is called insulin resistance. Furthermore, in diabetes mellitus the body frequently fails to produce enough insulin to control glucose levels. Whereas high insulin levels in human associated with cardiovascular disease, in horses the severe complication linked to this condition is the development of laminitis.
The exact process in which laminitis is developed consequently to insulin resistance is not completely understood. However, it is likely to be a damage and constriction of the blood vessels cells that will affect blood support to the hoof as well as a direct damage to the horn cells.
EMS is more common in certain breeds like Shetland, Dartmoor, Welsh and Morgan ponies and donkeys. Like diabetes mellitus type 2 in humans, it is less common in younger ages and it is associated with low exercise lifestyles and high sugar diets.
In both conditions, a presumptive diagnosis can be made based in the presence of overweight and history of related condition like laminitis in the horse. However, final diagnosis of EMS can be made by different laboratory testing.
- Measurement of basal insulin levels. This is achieve by taking a single blood sample. However, it can be normal in some horses so further test will need to be used (as the one described below).
- Testing insulin level as response to feed (Oral glucose/karo test): The horses are fed with some glucose in form of syrup and two blood samples are taken between 60-90 min after. This test will show the presence of post-prandial hyperinsulinemia. There are other dynamics test similar to this that require intra-venous administration of glucose are available but they are less easy to do in the field.
- Other tests that can be helpful in the identification of EMS is the detection in the blood samples of certain hormones like adiponectin which is a hormone associated to fat.
Differently to diabetes mellitus, in EMS glucose levels are not as important in the diagnosis as insulin levels are. However, some of the tests are similar.
For both condition, the treatment and prevention will be directed to management of diet and exercise. Therefore, the goal is to reduce weight and increase insulin sensitivity in tissues and their associated complications. EMS dietary restrictions are based on low soluble sugar and starches. Also exercise schedules are very important. Medical treatment of horses with insulin resistance is currently based on the use of metformine with is one of the drugs used in the treatment of diabetes mellitus type 2. This drug acts at the intestinal level limiting the high postprandial insulin.
As diabetes mellitus, EMS is an important condition with potential severe complications that require prompt detection and management but we are here to help so if you think your horse might have one of the risks factor mentioned before please give us a ring and we will be more than happy to help you.