Effect of dietary fructans and dexamethasone administration on the insulin response of ponies predisposed to laminitis

Objective-To determine whether pasture, and specifically the addition of fructan carbohydrate to the diet, induces exaggerated changes in serum insulin concentration in laminitis-predisposed (LP) ponies, compared with ponies with no history of the condition, and also to determine insulin responses to the dexamethasone suppression test. Design-Prospective study. Animals-10 LP and 11 control adult nonobese mixed-breed ponies. Procedures-Insulin-modified IV glucose tolerance tests were performed (5 ponies/group). In diet studies, ponies were kept on pasture and then changed to a hay diet (10 ponies/ group). Second, ponies were maintained on a basal hay diet (4 weeks) before being fed a hay diet supplemented with inulin (3 g/kg/d [1.4 g/lb/d]). Serum insulin and plasma glucose concentrations were analyzed before and after dietary changes. Serum cortisol and insulin concentrations were also measured in a standard dexamethasone suppression test. Results-The LP ponies were insulin resistant (median insulin sensitivity of 0.27 X 104 L.min(-1).mU(-1) in LP ponies, compared with 0.64 X 10(4) L.min(-1).mU(-1) in control ponies). Median insulin concentration in LP ponies was significantly greater than that in control ponies at pasture, decreased in response to feeding hay, and was markedly increased (5.5-fold) following the feeding of inulin with hay. The LP ponies had a greater increase in serum insulin concentration at 19 hours after dexamethasone administration (median, 222.9 mU/ L), compared with control ponies (45.6 mU/L). Conclusions and Clinical Relevance-Nonobese ponies predisposed to develop laminitis had compensated insulin resistance, and this phenotype was revealed by feeding plant fructan carbohydrate or by dexamethasone administration.