Nonstructural carbohydrates in tall fescue cultivars: Relationship to animal preference

Grazing animals prefer some plants to others. These choices are likely rela ted to physical and chemical factors such as energy-dense carbohydrates con tained in plants. This study quantified the nonstructural carbohydrate frac tions in each of eight vegetatively growing, endophyte-free, tall fescue cu ltivars (Festuca arundinacea Schreb.) and relates their sugar concentration s to cattle grazing preferences. The experimental area consisted of eight c ultivar 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 Sr. Freeze-dried forage samples we re extracted with hot water and an amylase (Clarase) solution. Sugars were quantified colorimetrically using potassium-ferricyanide and glucose-oxidas e methods. Cattle grazing preferences among these tall fescue cultivars wer e related to the concentrations of total nonstructural carbohydrates (TNC) (r(2) = 0.49, P < 0.05). Other sugar fractions mere not significantly relat ed to grazing preference in this study, The nonstructural carbohydrate conc entrations averaged over the entire study were glucose, 14; fructose, 5; su crose, 40; fructan, 23; insoluble starch, 24; and TNC, 129 g kg(-1). A fora ge selection criterion should include measures of the TNC because of their close relationship to animal grazing preference.