Metabolic and morphometric effects of psyllium supplementation in horses grazing rapidly growing cool season grasses

Abstract

Digestion of non-structural carbohydrates (NSC) from cool season pasture grasses can result in increased adiposity, insulin resistance, and laminitis in horses. Lowering blood glucose levels and increasing insulin sensitivity can reduce disease risk. Supplementing horses with psyllium reduces blood glucose and insulin concentrations in meal fed horses. The objective of this study was to evaluate the effects of psyllium supplementation in horses grazing rapidly growing cool season grass. Eleven lightbreed stock horses (7 mares, 4 geldings, Age 13.5 + or - 2.5; mean + or - SD) were individually confined in dry lots overnight and strip grazed for 8 hours daily for 30 days. Psyllium-supplemented horses (n = 6) received 180 g of psyllium daily. All horses received an isocaloric protein supplement. Forage intake was calculated using a previously published equation based on bodyweight. Forage was analyzed for nutrient content every other week. Changes in metabolic characteristics were assessed by assay of glucose, insulin, leptin and adiponectin concentrations in blood samples collected on days 0, 8, 15, 22, and 29 at 0700, 0800, 0900, 1100, 1300, and 1500 hours. Changes in morphometric characteristics were assessed using bodyweight, body condition score, mean neck circumference, and tailhead fat mass on days 0 and 29. Significance accepted at P < 0.05. Psyllium supplementation lowered mean glucose, glucose AUC and increased time to peak glucose. There was a treatment by gender interaction for mean insulin, peak insulin, and insulin AUC. These variables were lowered to a greater extent in geldings than in mares. Higher NSC intake resulted in higher peak insulin in all horses. Older horses had higher peak insulin and decreased time to peak glucose and insulin. All characteristics of glucose and insulin decreased over the 30 day interval spent grazing pasture. Mares had higher leptin concentrations. Adiponectin concentrations increased with NSC intake. No significant differences occurred for morphometric characteristics. These results indicate that supplementing psyllium in horses grazing cool season grasses lowered systemic glucose and insulin concentrations and these effects may reduce the risk of metabolic diseases, such as laminitis. However, systemic glucose and insulin concentrations were affected to a greater extent in males than females.