Variation in Protein and Fiber Fractions in Pasture During the Grazing Season

Abstract

This study was conducted to characterize the changes in chemical composition during the grazing season (June to September) of bromegrass (Bromus inermis), birdsfoot trefoil (Lotus corniculatus) plus bromegrass and unimproved pasture (26 species of forage, weeds and brush) when grazed at the vegetative stage of growth. Beef cows (Angus and Hereford) together with their nursing calves were rotated within each treatment; animals were added or removed as needed to keep each forage in the vegetative stage of growth. Following each grazing, all pastures were clipped 5 d after removing the cattle. Concentrations of CP increased and of fiber fractions decreased as the grazing season progressed. Protein solubility was highest in the first and last months. The percentage of the protein in the NDF fraction and that resistant to protease degradation varied with month of the grazing season, with highest levels occurring during midsummer (August).