Last Updated: | By Sarah Braithwaite, Author & Horse Health Expert
N0 horse laminitis is the goal of each ECIR Group conference. The ECIR Group lead the way in horse laminitis study through disseminating information that can help metabolic and endocrinopathic horses. ECIR is committed to providing high-quality information to achieve no horse laminitis, with scientific backing and real-life experience.
Forageplus attended No Laminitis conferences both to support the valuable work that the ECIR organisation is doing and also to learn and share the information with our customers. If you would like to join the ECIR Group because you want or need to know more about how to manage PPID (Cushings) or IR (Insulin Resistant) horses then please click here.
The fact that the signs and symptoms of these two conditions often over lap means that correct diagnosis is extremely important because they are treated differently.
Horses should not be fasted before testing serum glucose and insulin to diagnose IR (this is only done for human tests)! If a horse is “meal fed”, which basically means there are periods in excess of 6 hours when the horse has nothing to eat, the first meal after the fast will generate a larger insulin spike than subsequent closer together feedings even if the meal is exactly the same.
The best way of diagnosing PPID is by a single blood draw to measure the level of endogenous ACTH ( adrenocorticotrphic hormone). The sample however must be handled correctly so that it does not lead to a false negative. The sample should be put in a purple topped vial, placed on ice while it is taken straight back to the vets practice and then centrifuged and frozen. It should be then shipped frozen as soon as possible to the lab. In the UK Liphook is the best lab to use. Make sure your vet knows exactly how to handle and ship the sample so you do not end up with an unreliable result. If your vet suggests using the Dexamethasone Supression test which measures cortisol response, decline it as it may pose a risk of precipitating or exacerbating laminitis.
The best way of diagnosing IR is by obtaining a non-fasting glucose, insulin and leptin level from the same blood draw. Note that many vets insist on fasting your horse before this blood draw but this can lead to a false result. Horses should not be fasted before this testing (this is only done for human tests)! If a horse is “meal fed”, which basically means there are periods in excess of 6 hours when the horse has nothing to eat, the first meal after the fast will generate a larger insulin spike than subsequent closer together feedings even if the meal is exactly the same. To avoid a false positive result, the horse should have hay or pasture available at all times the night before and day of the testing. If that’s not possible, make sure the blood is drawn at least 4 hours after the first meal of the day and feed at 4 hour intervals or keep some hay in front of the horse until the testing is done. The horse should not be fed any hard feed prior to testing. The horse also should not be exercised within 4 hours of the test and avoid traveling before testing as well. Stress and exercise influence glucose, insulin and leptin dynamics.
Currently the only place offering leptin testing is Cornell University and Animal Health Diagnostic Laboratory in the U.S.A. but perhaps in the near future Liphook in the UK might start offering this test which is important due to the fact that raised leptin can be abnormal with normal insulin, so where a test comes back as within normal ranges for insulin and glucose, leptin levels can indicate early problems. Leptin is the hormone which signals fullness when eating. Horses can become leptin resistant meaning that high levels of leptin are produced in an effort to control over eating. Think of leptin as the ‘stop eating stupid hormone’! A low sugar and starch diet can influence insulin results. Testing leptin will help avoid a false negative in these cases.
Some important facts to remember:
Based on human studies and data from the ECIR Group member’s horses, the G:I ratio can be useful to diagnose your horse. You simply use the glucose and insulin result on the report. Divide the glucose result in mg/dL by insulin in uIU/mL. (If your insulin is reported in pmol/L you have to convert it to uIU/mL by dividing by 7.1.). A value below 4.5 is considered positive for IR and high risk of laminitis. Values between 4.5 and 10 represent compensated insulin resistance which means less risk of laminitis but it is wise to keep a tight control of diet and weight.
The RISQI is a proxy developed by researchers at Virginia Polytechnic Institute. RISQI stands for “reciprocal of the square root of insulin”. It is calculated by the equation 1/square root of insulin. A RISQI value of less than 0.2 is considered positive for IR and the horse is at high risk of laminitis. RISQI 0.2 to 0.32 = compensated insulin resistance and a lower risk of laminitis but again it is wise to keep a tight control of both diet and weight.
Horses that have elevated blood glucose, or abnormally low insulin responses, may have RISQI and G:I results that are normal because they have actually crossed the line from insulin resistance to actual diabetes. This is where calculating the MIRG value becomes extremely important.
MIRG = modified insulin:glucose ratio. It is calculated by: [800 0.3 x (insulin 50)2] /(glucose 30)]. If G:I ratio or RISQI are positive, there is no need to do this calculation, but if the horse has symptoms of IR and those equations are normal, you should check the MIRG, especially if blood glucose is elevated. A MIRG result greater than 5.6 means the horse is IR and at risk of laminitis.
Here you can find a very useful IR Calculator which is a tool designed to calculate the above G:I Ratio, RISQI and MIRG without you having to worry about knowing the maths.