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

Overview

• This study investigated how an oral glucose test (OGT) and different feeding conditions affect concentrations of high molecular weight (HMW) adiponectin in horses and ponies.
• The researchers found that the OGT increased post-prandial HMW adiponectin levels, while feeding pasture or other diets did not, indicating timing of blood sampling relative to glucose challenges is important for accurate adiponectin measurement.

Background

• Adiponectin: A hormone secreted by fat tissue (an adipocytokine) involved in regulating metabolism.
• High Molecular Weight (HMW) Adiponectin: A form of adiponectin thought to be more biologically active and important for metabolic regulation.
• Laminitis: A painful hoof disorder in horses linked to metabolic syndrome, with adiponectin levels potentially serving as a risk marker.
• Understanding how feeding and testing procedures affect adiponectin measurement is crucial for interpreting blood test results related to metabolic health in horses and ponies.

Study Objectives

• To assess the effects of an oral glucose test (OGT) on HMW adiponectin concentrations in horses and ponies.
• To determine how different types of feeding (pasture grazing, soybean meal diet, or maize/molasses diet) influence HMW adiponectin levels over time.
• To evaluate the relationship between total adiponectin and HMW adiponectin concentrations after glucose challenges and feeding.

Methods

• Participants: 85 horses and ponies underwent an OGT; a subset of 25 animals had total adiponectin measured.
• Sampling: Blood was collected before and after the OGT, specifically at 0 and 2 hours, and also before and up to 4 hours after consumption of three different diets in ponies:
  • Pasture grazing (n=16)
  • Soybean meal diet (n=10)
  • Maize and molasses diet (n=5)
• Assays used were validated specifically for horse plasma to ensure reliability of adiponectin measurements.
• Statistical analyses included Kruskal-Wallis and Dunn’s tests for group comparisons, signed-rank and Pearson’s tests for timepoint evaluations, paired t-tests for ratio changes, stepwise regression to identify predictors of change, and Friedman’s test for temporal changes after meals.

Key Findings

• Both the OGT and the diet containing maize caused significantly larger increases in blood glucose concentration over 2 hours compared to pasture or the soybean meal diet.
• The OGT significantly increased median post-prandial HMW adiponectin concentration at 2 hours (median 4.02 µg/mL) compared to the baseline (median 2.75 µg/mL), with a P-value <0.001 indicating strong statistical significance.
• Total adiponectin concentration did not show a significant change between 0 hours (7.78 µg/mL) and 2 hours (6.48 µg/mL) after the OGT.
• The proportion of HMW adiponectin within total adiponectin increased significantly from 37% to 54% after glucose administration (P=0.01), highlighting a shift in adiponectin composition.
• Pasture grazing and consumption of soybean or maize-based meals did not affect HMW adiponectin levels over time.

Interpretation and Implications

• The increase in HMW adiponectin—but not total adiponectin—after an in-feed OGT suggests that HMW adiponectin is a more sensitive marker of acute glucose-induced metabolic changes.
• The fact that only the OGT (and not regular feeding) caused a significant increase implies that glucose challenges provoke specific hormonal responses affecting adiponectin multimers in the bloodstream.
• Since feeding maize without an OGT raised blood glucose but did not change HMW adiponectin, the timing and method of glucose delivery may be important factors.
• For accurate measurement and interpretation of HMW adiponectin as a metabolic health biomarker, blood samples should be collected before animals undergo an OGT to avoid confounding effects caused by recent glucose intake.

Conclusions

• OGT administration impacts circulating HMW adiponectin levels, increasing its concentration and proportion in plasma post-prandially in horses and ponies.
• Feeding pasture or typical diets containing soybean or maize without glucose challenge does not alter HMW adiponectin concentrations acutely.
• Clinical and research practices measuring HMW adiponectin should standardize sampling timing relative to glucose challenges to ensure result validity.