Performance and Carcass Characteristics of Ram Lambs Slaughtered at Different Weights

Abstract

Feedlot performance and carcass data were obtained from 144 crossbred ram lambs slaughtered between 39.5 and 84.8 kg live weight. The lambs were fed in four groups determined by year and time of birth. When 12 lambs averaged 31.8 kg, they were placed in a pen and started on the trial. Three lambs from each pen were slaughtered at average pen weights of 45.4, 54.4, 63.5 and 72.6 kg. Carcass measurements were obtained and detailed carcass cutout data collected from the right side. Peformance data were analyzed by pen for the four weight gain intervals. Carcass data were analyzed by regression analyses of the various data on individual lamb live weights. Daily gain decreased (P<.05) and daily feed intake increased and then decreased (P<.01) as live weight increased from 31.8 to 72.6 kg. Consequently, the feed to gain ratio increased (P<.01) from 6.4 to 8.5 for the 31.8 to 45.4 and 63.5 to 72.6 kg weight intervals, respectively. All major carcass measurements and weights increased (P<.0001) in a linear manner as live weight increased. The kilograms of lean, fat and bone increased in the 72.6 kg lambs at a similar rate as in the 45.4 kg ram lambs. While percentage lean decreased 5.7% on a carcass basis, it declined only 1.2% on a live weight basis between 45.4 and 72.6 kg. This indicated the largest changes in percentage composition of the live animal were essentially a trade-off in offal items for carcass fat as lamb weight increased. Yield grade changes did not accurately identify changes in ram carcass lean yield. Carcass weight distribution among the wholesale cuts changed only slightly as live weight increased. Carcass quality scores increased, but Warner-Bratzler shear values for 36 lambs also increased. Although the shear data were quite variable, the values were in an acceptable range.