PERFORMANCE AND CARCASS CHARACTERISTICS OF WEANED LAMBS EITHER GRAZEDON ORCHARDGRASS, RYEGRASS, OR ALFALFA OR FED ALL-CONCENTRATE DIETS INDRYLOT

Four-paddock rotational grazing of orchardgrass, ryegrass, or alfalfa was compared to an all-concentrate diet fed in drylot using 202 weaned lambs. Comparisons of animal performance ended in each of the 3 yr (1 983, 1984, 1985) for all animals when drylot lambs reached a subjectiv e body condition score of 12 (range 1 to 15) and estimated fat depth o ver the rib was 5.5 to 7.0 mm. A total of 84 representative lambs were slaughtered over the 3 yr for carcass evaluation. Mature put-and-take ewes were used to maintain forages in the vegetative stage. Average d aily gain and total gain of lambs were in the order of drylot > alfalf a > grasses; performance of lambs grazing alfalfa approached performan ce of those fed the drylot diet. Better performance (P < .01) of lambs grazing alfalfa than of those grazing grasses is attributed to more C P (P < .01) and less NDF, ADF, and hemicellulose (P < .01) in alfalfa. Lambs grazed on grasses had smaller carcasses with less muscle, fat, and bone (P < .01) than either of the other two treatments. Although c arcasses of lambs grazed on alfalfa were lighter, they had the same mu scle mass as concentrate-fed lambs, indicated by leg conformation, lon gissimus muscle area, and by physically separated absolute muscle weig ht. However, these carcasses contained less fat (P < .01) and had more desirable yield grades (P < .01) than the carcasses of concentrate-fe d lambs.