Submitted to: Journal of Production Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 30, 1997
Publication Date: N/A
Interpretive Summary: 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 meats have shifted the emphasis to leaner, trimmer carcasses produced from livestock production systems utilizing forage crops. We compared weight gain and carcass characteristics when lambs grazed grass/legume autumn pasture or were fed grain in the feedlot. Although lambs grazing pasture had lower weight gain and body weights, carcasses from lambs grazing pasture had 14% less fat and about 8% more protein compared to grain-fed lambs. Percent- age of white clover in the sward may have influenced the proportion of individual fatty acids in lean and fat tissues. This work will benefit scientists trying to develop metabolic partitioning agents to manipulate fat and lean proportions in production livestock. It will benefit our economy by reducing reliance upon expensive grain supplements and encouraging producers to use grasslands more wisely to be more cost effective.
Technical Abstract: Performance of livestock grazing pasture is variable. Pastures must be managed to optimize quantity and quality of herbage to meet nutrient requirements of a specific class of livestock. Consumer desires for healthier meats have shifted the emphasis to leaner, trimmer carcasses produced from livestock production systems utilizing 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 performance and carcass quality when grazing autumn pasture or fed concentrate in feedlot. Less CP from white clover was available for use by grazers in 1992 than in 1991. Frequent clipping of autumn pasture resulted in herbage with greater nutritive value (lower NDF and higher IVOMD) compared to more mature stockpiled herbage. A computer model predicted greater potential for lamb growth on intensively managed (clipped) vs. stockpiled herbage. Lambs fed grain had greater (P < 0.05) cumulative weight gain, ADG, slaughter weights, chilled carcass weights, dressing percentages, leg conformation scores, REA, fat over rib, KHP fat, quality and yield grades, and shear force compared to lambs grazed on autumn pasture. However, carcasses from lambs grazing pasture in autumn had 14% less fat and about 8% more protein when compared to lambs fed grain. While total fat content of carcasses was lower for pasture-grazed rather than grain-fed lambs, saturated fatty acid composition and choles- terol levels were greater. Percentage legume in the sward may have influ- enced the proportion of individual fatty acids in lean and fat. Market weight animals may be produced from botanically complex autumn pasture.