Oral Sugar Test

By Donald M. Walsh, DVM

The Oral Sugar Test (OST) is a simple new procedure which tests horses’ insulin level in response to eating sugar – it can predict whether eating grass may lead to equine laminitis. A dose of corn syrup is administered to the horse which has been fasted, then blood samples are taken 60 and 90 minutes later which will be analyzed for the insulin and blood glucose levels. If both test results show the insulin is less than 45 uU/ml and the blood glucose is less than 125 mg/dL, considered normal results, it indicates the horse is currently at low risk to develop laminitis from eating grass.

These are the steps in administering the Oral Sugar Test:

  1.  The horse owner calculates the horse’s weight in kilograms using this formula:

       HG x HG x L
             330            =    weight in pounds
                                                2.2                 =  weight in kilograms

         Formula notes: Multiply horse’s heart girth by horse’s heart girth by horse’s length. Divide this number by 330 to get the weight in pounds. Divide the weight in pounds by 2.2 to     get the horse’s weight in kilograms. (See drawing showing how to measure Heart Girth and Length.)

      2. The horse’s weight in kilograms is reported to the veterinarian who will determine the dose of Karo Light Corn Syrup to be administered by dose syringe. (The dose of syrup is figured at a ratio of .15 ml syrup per 1 kg of weight of horse. The amount of syrup given ranges from half an ounce to 3 ounces, depending on the size of horse or pony.)

3. The owner picks up the dose syringe of Karo Syrup from the veterinarian and arranges a date and time with the vet for the Oral Sugar Test to be performed. The vet is scheduled to arrive on that date 60 minutes after the dose of syrup will be given.

4. On the day of the test, the horse is to be fasted (not fed) at least 3 hours before the test will be done. Sixty (60) minutes prior to the arrival of the vet, the owner slips the dose syringe into the side of the horse’s mouth and administers the dose of Karo Light Corn Syrup onto the horse’s tongue, much as an oral dewormer is given. Continue to withhold feed until after the vet has arrived.

5. The veterinarian arrives 60 minutes later for the pre-arranged appointment and blood samples are taken from the horse being tested.

6. The blood samples

 will then be analyzed to determine the insulin and blood glucose levels.

The owner and veterinarian work together to accomplish this test. The OST is superior to earlier Fasting Insulin tests because it gives more meaningful results. An owner can allow a ‘normal’ horse to eat grass, knowing there is low probability of laminitis developing.

A positive test result (numbers above 45 and 125 respectively for insulin and blood glucose) can warn the owner and veterinarian that laminitis is a possibility and further testing and diet management consultation are indicated.

(Click on picture to enlarge)