A modified oral sugar test for evaluation of insulin and glucose dynamics in horses

Background: An oral sugar test (OST) using Karo (R) Light Corn Syrup has been developed in the USA as a field test for the assessment of insulin dysregulation in horses but the syrup is not available in Scandinavian grocery stores. The aim of the study was to compare the results of a modified OST between horses with equine metabolic syndrome (EMS) and healthy horses using a Scandinavian commercially available glucose syrup (Dansukker glykossirap). In addition, the effect of breed and the repeatability of the test were evaluated. In the present study, clinically healthy horses (7 Shetland ponies, 8 Icelandic horses, 8 Standardbred horses) and 20 horses of various breeds with EMS underwent the modified OST test. The Icelandic horses and Shetland ponies underwent the OST twice. Insulin and glucose data from the OST were used to calculate peak insulin concentration (Peak(INS)), time to peak insulin concentration (T-peak(INS)), area under the curve for insulin (AUC(INS)) and glucose (AUC(GLU)) as well as whole body insulin sensitivity index (ISICOMP).Results: Compared to the healthy group, the EMS group had 6-7 times higher geometric mean for Peak(INS) and AUC(INS) and 8 times lower geometric mean for ISICOMP. The EMS group had a delayed T-peak(INS) compared to the healthy group. There was no effect of breed in the group of healthy horses on Peak(INS), T-peak(INS), AUC(INS), AUC(GLU) and ISICOMP. Coefficient of variation for repeated tests was 19.8, 19.0 and 17.6 % for Peak(INS), AUC(INS) and ISICOMP respectively.Conclusions: The results of the present study demonstrate that the modified OST appears to be a practical and useful diagnostic tool for assessment of insulin dysregulation in the horse. However, to make it possible to establish the most appropriate sampling interval and to evaluate the accuracy of the modified OST, further studies in horses with a variable degree of insulin resistance are needed, where results from the modified OST are compared with quantitative measurements for IS.