Identifying Equine Metabolic Syndrome in New Zealand - Dr Michelle Logan

Equine Metabolic Syndrome (EMS) is a common condition in both horses and ponies.

The main problem that we see in ponies with EMS is extremely sore feet because of laminitis (founder), but EMS does cause other issues too. Many of you will be familiar with fat ponies that foundered in the past and were put in the so called ‘starvation paddock’ to lose weight, but we now know a lot more about what is actually going on (although there is still a lot more research to be done!).

Why do fat ponies founder?
Although horses and ponies with EMS do tend to be fat or have areas of fat deposits (e.g. a fatty neck crest or perhaps cellulite-like fat over their rump), they do not have to be fat to have EMS. Being overweight is a risk factor for EMS but the cause is all to do with insulin. Veterinary researchers have found that there is a problem with the control of insulin in the blood of EMS affected horses and ponies, which they call ‘insulin dysregulation’. Insulin is produced when there is increased glucose (sugar) in the blood stream, which happens after eating, especially after a high sugar meal. In EMS-affected horses and ponies the amount of insulin produced is considerably higher than in a normal horse.

Why is increased insulin a problem?
Research has shown that continuously high levels of insulin in the blood stream of even a normal horse will cause laminitis. This is despite the blood sugar level being in the normal range. There are a few theories as to how a prolonged increase in blood insulin level causes laminitis, but no definite answer has been found yet. A short-term elevation in blood insulin level doesn’t seem to cause laminitis.

Because EMS-affected horses and ponies produce a significantly higher amount of insulin than in a normal horse after a sugar meal this can be used as a test to see which horses and ponies are affected by EMS. Once we know which horses and ponies are at risk, management changes can be made to reduce the risk of laminitis episodes and in many cases we can get the insulin response back into the normal range (or at least closer to it). This often means taking ponies off grass and feeding soaked hay for a period of time, as New Zealand pasture often contains high levels of sugar.

NZERF Research project
The aim of this study was to find out what the insulin response to a glucose meal is in normal NZ horses and ponies compared to horses and ponies with EMS. We would then be able to identify the upper reference range cut-off point for blood insulin in normal horses, which would help with the diagnosis of EMS – any horse with a blood insulin level above the cut-off point would be positive for EMS.

Ten normal horses (called controls) and ten suspected EMS cases were tested in their home environment and at the same time of year as each other. This was to rule out the effect of stress or season variation affecting the results. All horses were taken off grass and fasted overnight (water was freely available). A base-line blood sample was taking in the morning before feeding a measured amount of glucose powder in a small amount of low sugar feed (e.g. chaff or non-molassed beet). Two hours later a second blood sample was taken, after which the horses could return to normal. Both blood samples were tested for glucose and insulin levels.

What were the results?
There was a significant difference between the blood insulin levels of suspect EMS cases and normal horses after a glucose meal, with the suspected EMS cases having higher levels of insulin in the blood. Although this is what we expected, to see it in real life was quite dramatic as often the EMS affected horses and ponies looked quite normal if they were being managed well and yet, internally, there was a definite difference in the way their bodies responded to sugar. The reference range for blood insulin levels after a glucose meal for normal horses in NZ was < 35mIU/L. New Zealand veterinarians will now be able to use this cut-off value for blood insulin level after glucose meal to aid in the diagnosis of EMS cases. This will allow better treatment plans for affected horses, improve their quality of life and even save the lives of horses and ponies affected by Equine Metabolic Syndrome.

What do you do if you think your horse or pony may have EMS?
Please contact your veterinarian. They will be able to perform this straightforward test on your horse/pony. Now that we know the cut-off value, this test only needs the second blood sample and so only one vet visit is required. Your vet will use the results to advise you on a treatment and management plan, and the test can be repeated to monitor your horse’s progress.

I would like to thank the NZERF for funding this important study.