Canopy Management Influences on Cool-Season Grass Quality and Simulated Livestock Performance

Inadequate energy intake across the grazing season can be a major limitation to performance of grazing ruminants. A small-plot experiment was conducted to determine the effect of repeated defoliation, based on canopy height and on the quantity and quality of tall fescue × perennial ryegrass (Festuca arundinacea Schreb. × Lolium perenne L.) hybrid, orchardgrass (Dactylis glomerata L.), and prairie grass (Bromus catharticus M. Vahl) in the Central Appalachian Region of the USA. Energy determined from herbage quality data was used to predict growing steer performance. Early and repeated defoliation (T50, 20-cm canopy cut to 10-cm residue; S50, 10-cm canopy cut to 5-cm residue; and T75, 20-cm canopy cut to 5-cm residue) of the grasses resulted in greater herbage crude protein (CP) (202, 226, and 189 g kg⁻¹, respectively) and lower neutral detergent fiber (NDF) concentrations (591, 572, and 596 kg⁻¹, respectively) compared with the hay management (hay harvested at early seed head emergence followed by T75 management; 152 g CP kg⁻¹ and 620 g NDF kg⁻¹). Cumulative metabolizable energy yield on a 1000-ha basis tended to be highest for hay (62 138 MJ ha⁻¹) and T75 (49 678 MJ ha⁻¹), compared with S50 (40 373 MJ ha⁻¹) and T50 (28 457 MJ ha⁻¹) simply because of greater herbage mass. Greatest average daily gain was predicted when 250-kg steers grazed T50 (0.81 kg d⁻¹) compared with S50 (0.70 kg d⁻¹) and T75 (0.71 kg d⁻¹). Total number of grazing days per hectare was lowest for T50 (431 d), compared with S50 (580 d) and T75 (690 d). Total annual gain was greater for T75 (690 kg liveweight ha⁻¹) management than for S50 (580 kg ha⁻¹) or T50 (436 kg ha⁻¹). Using herbage earlier in spring before maturation may compromise total herbage productivity, but should sustain a greater number of grazing days and livestock productivity for a given land area.