An in-feed oral glucose test increases post-prandial high molecular weight adiponectin concentration in horses

Adiponectin is a fat-derived adipocytokine that has been associated with laminitis risk in ponies. Factors that affect sampling timing for measurement of adiponectin concentration have been inadequately investigated. This study aimed to determine the effect of an oral glucose test (OGT) and fed-state on adiponectin concentration in horses and ponies. Blood samples were collected before and after an OGT in 85 horses and ponies and high molecular weight (HMW) adiponectin concentration was measured. Total adiponectin concentration was measured in a subset of 25 animals. Assays validated for use with horse plasma were used. Next, HMW adiponectin was measured before and for up to 4 hours after the consumption of three different diets in ponies: pasture (n = 16), a soyabean meal diet (n = 10) or diet with added maize and molasses (n = 5). The groups were compared with a Kruskal Wallis rank sum test, with Dunn's post-hoc test, and timepoints with a signed-rank, or Pearson's, test. The ratios were compared with a paired t-test. Stepwise rank-based regression was used to consider multiple predictors for the change in HMW adiponectin concentration during the OGT. Friedman's test was used to examine changes in concentration over time after meal consumption. Both the OGT and the diet containing maize caused a larger (P < 0.05) change in blood glucose concentration (0h to 2h) than the pasture or diet with soyabean meal. The OGT meal increased (P < 0.001) median [IQR] post-prandial HMW adiponectin concentration at the 2 h timepoint (4.02 [2.23-6.88] µg/mL), compared to the pre-test sample (2.75 [1.17-5.69] µg/mL). However, median [IQR] total adiponectin concentration did not change from the 0 h (7.78 [4.19-12.7] µg/mL) to the 2 h sample (6.48 [4.04-12.8] µg/mL). The proportion of HMW multimers in the total adiponectin concentration increased (P = 0.01) from 37% to 54% post-prandially. Pasture grazing and consumption of a soyabean or maize based meal did not result in a change in HMW adiponectin concentration over time. Blood samples for the measurement of HMW adiponectin should be taken before animals receive an in-feed OGT.