Glucose and Insulin Response of Aged Horses Grazing Alfalfa, Perennial Cool-Season Grass, and Teff During the Spring and Late Fall

Abstract Spring and late fall grazing can lead to metabolic problems in horses ( Equus caballus L.) as a result of elevated nonstructural carbohydrates (NSC) in pastures. Therefore, the objectives were to determine the impact of different forage species on blood glucose and insulin concentrations of horses during the spring and late fall. Research was conducted in May (spring) and October (late fall) in St. Paul, MN. Alfalfa ( Medicago sativa L.) and mixed perennial cool-season grasses (CSG) were grazed in spring, and CSG and teff ( Eragrostis tef [Zucc.] Trotter) were grazed in late fall by six adult horses randomly assigned to a forage in a cross-over design. Jugular catheters were inserted 1 hour before the start of grazing, and horses had access to pasture from 8 AM to 4 PM in the spring and 8 AM to 12 PM in the late fall. Jugular venous blood samples were collected from each horse before being turned out (0 hours) and then at 2 hours intervals after turnout. Plasma and serum samples were collected and analyzed for glucose and insulin, respectively. Corresponding forage samples were taken by hand harvest. Seasons were analyzed separately, and data were analyzed using the MIXED procedure in SAS with P ≤ .05. Teff had lower NSC compared with CSG in the late fall ( P ≤ .05) with subsequently lower average glucose, average insulin, and peak insulin in horses grazing teff compared with CSG ( P ≤ .05). These results suggest grazing teff could lower the glucose and insulin response of horses during late fall.