Autumn-grazed orchardgrass-white clover pasture: nutritive value of herbage and lamb performance

Performance of livestock grazing pasture is inherently variable. Pastures must be managed to optimize quantity and quality of herbage to meet the nutrient requirements of a specific class of livestock involved in a defined production goal. Consumer desires for healthier meat products have shifted the emphasis to lean, trim carcasses from livestock production systems using forage crops. The purpose of this study was to characterize herbage nutritive value changes in grass-legume pastures grazed during autumn and to compare growing lamb (Ovis aries) performance and carcass quality when grazing autumn pasture or fed concentrate in feedlot. Less crude protein (CP) from legume was available for use by grazers in 1992 than in 1991. Frequent clipping of autumn pasture resulted in herbage with greater nutritive value (lower neutral detergent fiber [NDF] and higher in vitro organic matter disappearance [IVOMD]) than more mature stockpiled herbage. A computer model of energy determined from acid detergent fiber (ADF) nutritive value and herbage mass data predicted greater potential for lamb growth on intensively managed (clipped) vs. stockpiled herbage. Lambs fed grain had greater (P 0.05) cumulative weight gain, average daily gain (ADG), slaughter weights, chilled carcass weights, dressing percentages, leg conformation scores, ribeye area (REA), fat over rib, quality grade, and yield grades than lambs grazed on autumn pasture. However, carcasses from lambs grazing pasture in autumn had 14% less fat and about 8% more protein than lambs fed grain. While total fat content of carcasses was lower for pasture-grazed than grain-fed lambs, saturated fatty acid composition and cholesterol concentrations in lean tissue were not different. Percentage legume in the sward may have influenced the pro-portion of individual fatty acids in lean and fat. Market weight lambs may be produced from botanically complex autumn pasture