Which forage to feed horses with EMS?

Last Friday I attended the Hippocampus day at Ultuna and listened to Johan Bröjer who is associated professor in internal medicine in horses and works at the Department of Clinical Sciences, SLU. Very pedagogically Johan described how insulin resistance works, criteria for EMS, what we know today and recommendations for how these horses should be fed. I will try to share parts of his lecture.

EMS is short for equine metabolic syndrome and the main criteria for a horse to have EMS is: insulin resistance (IR), general obesity and/or regional adiposity and the horse should have laminitis or increased risk of developing laminitis (which is not related to other diseases such as retained placenta, diarrhea, shipping fever etc.).

Insulin resistence (IR)

One of the most important criteria for diagnosing EMS is insulin resistance. The definition for IR is: reduced ability to at a given insulin concentration lower blood sugar levels. When a healthy horse eats the concentration of blood glucose increase and insulin is released, which enables glucose to be absorbed and stored as glycogen in muscle cells and as fat in fat cells. When a horse with IR eats this process is impaired. A horse with IR has low insulin sensitivity which means that very large amounts of insulin might have to be released in order to ensure that blood glucose is taken care of. In horse IR is compensated, the horse has low insulin sensitivity and an abnormally high insulin response at glucose (sugar) intake, e.g. with the sometimes extremely high insulin response it manages to keep blood sugar levels in check. In some individuals the compensated IR can develop into type 2 diabetes.

Obesity

Regional adiposity during EMS is shown mainly in the neck, behind the shoulder blades, the area close to the tail head and in the prepuce or mammary gland region. For a long time scientist have suspected that general obesity plays a role in development of EMS since increased adipose tissue increase the local and systemic inflammatory response, which leads to IR and metabolic disorders. However, more recent studies have not been able to show a straightforward correlation between obesity and inflammatory markers. Practical studies have been performed where horses were made overweight and it did not appear to cause IR. Studies have also shown that fat ponies that were put on a diet and reduced weight improved their insulin sensitivity. Therefore there is now a new revised clinical picture of the EMS patient; all overweight horses do not have EMS and all horses with EMS do not have general and/or regional adiposity. This implies that weight loss can result in improved insulin sensitivity but the underlying metabolic disorder probably stays.

Which horses develop EMS?

The ability to develop EMS is probably tied to breed and it is mainly the more easy kept breeds that are predisposed. The horse breeds that seems to more easily get EMS are among others Dartmoor, Welsh pony, Shetland pony, Icelandic horse, Arabian thoroughbred, Tennesse Walking horse, Morgan horse, Pura Raza Espanola and Paso Fino. Obesity does not seem to be the direct cause of EMS. Obesity is rather a marker for an underlying metabolic disorder which in interactivity with environmental factors such as wrong feeding practice and lack of exercise results in obesity and regional adiposity.

Treatment of horses with EMS

In horses there is no successful treatment with medical products to improve insulin sensitivity. What can be done is changes in management, exercise and feeding. Increased exercise is important but can also be difficult with horses suffering from laminitis. Physical activity results in weight loss and improved insulin sensitivity.
The fat EMS patient should be put on a diet to decrease its adipose tissue, which can improve the insulin sensitivity but probably the horse will still have the underlying metabolic disorder. To successfully get a horse to lose weight is easier said than done but a rough guideline can be to decrease the feed ration to about 75-85% of maintenance (MJ).

Remove starchy concentrate (cereal based, oat, barley) and concentrates rich in sugar (molassed sugar beet pulp), and use later harvested forage as low in sugar as possible. The forage can also be mixed with straw. Distribute the daily feed ration as evenly as possible over the 24 hours of the day and try to prolong the eating time. To feed this way aims at decreasing the insulin response in horses with EMS, as they in opposite to healthy horses have an abnormally high insulin response. High insulin response after feeding increase the risk of laminitis in EMS horses.

It is not always enough to feed forage with low sugar content, some individuals have shown enormous insulin responses even after feeding forage low in sugar. It seems to be more important to distribute the feed ration in small portions evenly over the 24 hours. Also it is important not to forget that when it comes to healthy horses we do not have to be afraid of sugar, forage high in sugar and protein can be beneficial for athletic horses.

Pasture implies an uncontrolled intake of nutrients and therefore also an uncontrolled intake of sugar and uncontrolled high insulin response. It also makes dieting more difficult. Therefore the recommendation is that horses with EMS should not be let out on pasture until the IR has significantly improved.

Sara Muhonen, AgrD

Reference:
Bröjer J 2014 Vad är ekvint metabolt syndrom? Hippocampusdagen 14 november 2014, aktuell hästforskning vid SLU och SVA, Hippocampus Hästar, Uppsala. (In Swedish)