Nutrient quality of bluebunch wheatgrass regrowth on elk winter range in relation to defoliation

Abstract

Effects of defoliating bluebunch wheatgrass (Agropyron spicatum [Pursh] Scribn. & Smith) to increase the quality of regrowth available on Rocky Mountain elk (Cervus elaphus nelsoni Bailey) winter range were studied from 1988 through 1990. Percent calcium, phosphorus, in vitro dry matter digestibility (IVDMD), and available forage (kg/ha DM) of regrowth present on control, spring-defoliated, and fall-defoliated plots were determined in November of 1988 and 1989, and April of 1989 and 1990. Spring conditioning did not affect the percentage of calcium and phosphorus, or available forage compared to the current year's growth in either November or April. Fall conditioning increased digestibility and increased the phosphorus concentration, but decreased available forage compared to the control and spring-conditioned forage in November. Fall conditioning may create a deficit of forage if regrowth is not achieved. Additional research is needed on defoliation during the early phenological time-period of bluebunch wheatgrass to improve the forage quality of elk winter ranges.