Effect of increased adiposity on insulin sensitivity and adipokine concentrations in horses and ponies fed a high fat diet, with or without a once daily high glycaemic meal

Reasons for performing studyThe relative influences of obesity and adaptation to high glycaemic diets on the development of insulin dysregulation in equids are unclear. ObjectivesTo determine whether increased adiposity per se is responsible for the decreased insulin sensitivity often observed in obese horses or whether a dietary glycaemic response is critically important. Study designRandomised controlled trial. MethodsEighteen horses and ponies were studied over a 20-week period. They received adlibitum hay plus either a high fat (low glycaemic) diet (FAT; n=6) or a similar (isocaloric) diet containing 1.5g/kg bwt once daily glucose (GLU; n=6) to induce obesity. A third group received a control ration (CON; n=6). Adiposity was monitored using body condition score (BCS) and total body fat mass percentage (TBFM) determined using a deuterium oxide dilution technique. Insulin sensitivity was assessed using a frequently sampled i.v. glucose tolerance test. Plasma concentrations of glucose, insulin, leptin, adiponectin, tumour necrosis factor- (TNF-) and serum amyloid A (SAA) were measured. ResultsThe FAT and GLU groups became obese (BCS 7) whereas the CON group maintained moderate condition (BCS 6). Total body fat mass and leptin concentrations were increased in the FAT and GLU groups than in the CON group (P<0.001 and P=0.003, respectively). Values for both insulin-dependent (SI) and insulin-independent (Sg) glucose disposal were higher in the GLU group compared with the FAT and CON groups (P=0.006 and P=0.03, respectively). There were no differences in adiponectin, TNF- or SAA between groups (all P0.4). ConclusionsIncreased adiposity did not reduce insulin sensitivity in either the FAT or the GLU diet groups, suggesting that obesity per se might not be responsible for the lower SI values reported in previous studies. Contrary to expectations, once daily glucose appeared to increase insulin sensitivity. Further work is required into the dietary causes of insulin resistance in equids.