Comparison of Plasma Active Glucagon-Like Peptide 1 Concentrations in Normal Horses and Those With Equine Metabolic Syndrome and in Horses Placed on a High-Grain Diet

Abstract

Hyperinsulinemia is associated with laminitis in horses, and active glucagon-like peptide 1 (aGLP-1) stimulates insulin secretion. We hypothesized that plasma aGLP-1 concentrations measured during an oral sugar test (OST) would differ significantly between normal horses and those with equine metabolic syndrome (EMS) and that aGLP-1 concentrations would increase when EMS horses were placed on a high-grain diet. An enzyme-linked immunosorbent assay for aGLP-1 was validated with equine plasma and six horses with EMS, and 10 healthy Quarter horse crossbred mares were compared. Eleven months later, the same horses with EMS were placed on a high-grain diet for 8 weeks and aGLP-1 concentrations were measured during an oral glucose tolerance test at 0 and 8 weeks. Frequently sampled intravenous glucose tolerance tests were also performed. The assay was validated with equine plasma and concentrations increased during the OST. Area under the aGLP-1 curve did not differ between normal and EMS horses. There was a weak trend (P = .097) toward a higher maximum percentage increase in aGLP-1 concentrations during the OST in EMS horses compared with normal horses. Body weight increased (P = .031) after 8 weeks when EMS horses were placed on a high-grain diet. Resting (fasted) insulin concentrations significantly increased (P = .012), but plasma aGLP-1 concentrations did not change significantly. Our hypotheses were not supported because plasma aGLP-1 concentrations did not differ significantly between normal horses and those with EMS and did not increase when EMS horses were placed on a high-grain diet for 8 weeks. However, a trend toward higher percentage increases in aGLP-1 concentrations during the OST was detected in EMS horses, compared with normal horses, and this warrants further investigation.