Summary Reasons for performing study The in‐feed oral glucose test ( OGT ) and oral sugar test ( OST ) are advocated as field tests of insulin sensitivity in horses and ponies but have not been directly compared. Objectives To compare the insulin response to OGT and OST in 8 ponies and 5 horses of unknown insulin sensitivity. Study design Experimental, randomised crossover study. Methods Animals were fasted for 8 h overnight before and throughout testing. They were fed 1 g/kg bwt glucose powder with chaff ( OGT ) or 0.15 ml/kg bwt corn syrup ( K aro™ L ight S yrup; OST ) was administered per os in a randomised crossover study with 48 h between tests. Blood samples were obtained at 0, 30, 60, 75, 90, 120 and 180 min. The maximal insulin concentration ( C max i ), time to maximal insulin concentration ( T max i ) and area under the curve of insulin concentration over time ( AUC i ) for the tests were compared using Student's paired t test. The effect of individual subject, horse or pony and test were analysed using a linear mixed model. Results The OGT C max i (mean ± s.d.; 154 ± 116 μiu/ml), T max i (136 ± 52 min) and AUC i (15,308 ± 9886 μiu/ml/min) were significantly (P<0.05) greater compared with the OST C max i (72 ± 55 μiu/ml), T max i (63 ± 25 min) and AUC i (5980 ± 4151 μiu/ml/min). The C max i , T max i and AUC i varied significantly between individual subjects. The T max i was significantly different between horses and ponies during OGT and OST . Using previously defined criteria of insulin dysregulation, OGT identified 7/13 animals as insulin resistant, whereas OST identified 5/13 animals as insulin resistant. Conclusions The OGT and OST showed agreement in identification of insulin dysregulation in 85% of equine subjects. Results of the OGT and OST are not comparable in all cases. Further work is required to establish which test more accurately diagnoses insulin dysregulation in horses and ponies.