(E26) Serum Total Adiponectin Variation over 24 Hours in Grazing Horses with and Without Insulin Dysregulation

Abstract: Background– Serum insulin varies in response to pasture nutrient content across the day in grazing horses; therefore, sample timing can greatly influence results. Total adiponectin is a potentially useful marker of insulin dysregulation (ID) and laminitis risk, but its temporal variability in grazing horses is unknown. Hypothesis/Objectives- To examine temporal changes in serum total adiponectin over a 24 hour grazing period in horses. Animals– Twelve adult horses (mean±s.d. 19±3yrs) pre-classified as ID (n=6) or non-ID (NID; n=6) using oral sugar tests. Methods– Horses were housed on pasture in late summer. Blood was collected every 2 hours for 24 hours and analyzed for insulin (Tosoh AIA) and total adiponectin (turbidimetric immunoassay). Data were analyzed non-parametrically. Results– Pasture non-structural carbohydrate (NSC) varied from 7.5-15.4% (dry matter basis). The median [interquartile range] total adiponectin (µg/ml) was higher in NID (10.5 [6.7-13]) compared to ID (4.8[3.9-6.5]) horses (P< 0.001) and varied minimally across the day (median [IQR] within-horse total range 0.8[0.7-1] for NID and 0.6[0.5-0.8] for ID; within-horse coefficient of variation 2.6%[2-3.6] for NID and 3.5%[2.6-5.9] for ID). In contrast, insulin (µIU/ml) varied widely over the day (median [IQR] within-horse total range 16[3.6-19.7] for NID and 168[122-235] for ID; within-horse coefficient of variation 17%[6.9-18.8] for NID and 32.3%[26.6-41.4] for ID). Initial adiponectin concentration negatively correlated with peak insulin (r=-0.70[95%CI -0.91 to -0.17];P=0.02). Conclusions and clinical importance– Factors causing variation in insulin concentrations in grazing horses in late summer had minimal effects on total adiponectin. The effect of pastures with higher NSC contents warrants evaluation.