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) (r2 = 0.49, P < 0.05). 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
