Nonstructural Carbohydrates in Tall Fescue Cultivars: Relationship to Animal Preference

Abstract

Grazing animals prefer some plants to others. These choices are likely related to physical and chemical factors such as energy‐dense carbohydrates contained in plants. This study quantified the nonstructural carbohydrate fractions in each of eight vegetatively growing, endophyte‐free, tall fescue cultivars ( Festuca arundinacea Schreb.) and relates their sugar concentrations to cattle grazing preferences. The experimental area consisted of eight cultivar plots replicated three times in each of three pastures. Within each pasture, forage was sampled between 0830 and 1000 h mountain daylight time (MDT) during each of four seasons and 2 yr. Freeze‐dried forage samples were extracted with hot water and an amylase (Clarase) solution. Sugars were quantified colorimetrically using potassium‐ferricyanide and glucose‐oxidase methods. Cattle grazing preferences among these tall fescue cultivars were related to the concentrations of total nonstructural carbohydrates (TNC) Other sugar fractions were not significantly related to grazing preference in this study. The nonstructural carbohydrate concentrations averaged over the entire study were glucose, 14; fructose, 5; sucrose, 40; fructan, 23; insoluble starch, 24; and TNC, 129 g kg −1 . A forage selection criterion should include measures of the TNC because of their close relationship to animal grazing preference.