Forage composition and intake by steers grazing vegetative regrowth in low endophyte tall fescue pasture.

Abstract

A grazing trial was conducted with six half-sib yearling Angus steers (average initial weight 281 kg) to quantitate nutrient composition and voluntary intake of vegetative regrowth forage in low-endophyte (Acremonium coenophialum Morgan-Jones and Gams) Kentucky-31 tall fescue (Festuca arundinacea Schreb.) pasture. A new .6-ha section in each of two 3.0-ha pastures (three steers/pasture) was clipped to a 5-cm height on five consecutive days to establish a series of plots that could be grazed continuously during 5-d test periods at uniform stages of vegetative regrowth; each period represented a specific regrowth stage (7, 14, 21, 28 and 35 d). Steers were conditioned by training them to graze to satiety while tethered with an adjustable-length rope to a 1-m galvanized steel post. Grazing time was limited to two sessions daily beginning at 0800 and 1400, and satiety was achieved after no more than 2.5 h of continuous grazing in each session. Forage DM availability was controlled by adjusting tether length and was set each day at 4% of steer BW. Fecal DM output was measured by chromic oxide dilution. A quadratic (P less than .05) effect of regrowth stage was observed for forage contents of NDF and ADF due to abrupt increases in both fractions at wk 5; values for ADL were unaffected by stage of forage regrowth. Forage contents of CP and ash showed a cubic (P less than .05) response to advancing stage of regrowth, with highest (23.6 and 11.0%, respectively) and lowest (14.7 and 9.1%, respectively) values for both fractions occurring at wk 1 and 5, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)