Seventy-two mature, nonpregnant, nonlactating Hereford cows (400 kg) were utilized in a comparative slaughter trial to investigate the effects of carcass composition on the metabolizable energy (ME) required for maintenance in winter. Body condition score (CS), live weight (LW) and weight:height ratio (WTHT) were evaluated and compared as estimators of carcass composition in cows. Cows ranged in LW, CS and WTHT from 275 to 595 kg, 2.0 to 8.0 units and 2.29 to 4.62 kg/cm, respectively. Live weight, CS and WTHT predicted total carcass energy (TMCAL, r2 = .81, .85 and .83), carcass fat (FAT, r2 = .78, .82 and .80), carcass protein (PRO, r2 = .71, .74 and .70) and carcass water (WAT, r2 = .78, .71 and .77) with similar accuracy. When composition was expressed on a per unit weight basis, CS was superior to LW and WTHT as predictors of TMCAL/hot carcass weight, TMCAL/LW and FAT/hot carcass weight (r2 = .82, .60 and .64; .83, .58 and .62; and .82, .64 and .68, respectively). Forty-seven cows were individually fed a complete diet (2.50 Mcal ME/dry matter) in drylot for 114 d in yr 1 and 115 d in yr 2. Daily feed intakes were adjusted each week to maintain constant LW throughout the winter. Data were analyzed by fitting the model: ME intake = k-1 (carcass energy change) + f(CS)LW.75, where k = efficiency of ME use for carcass energy change and f(CS) = function of CS. Year as a class variable and the expression .1028 + .0234(CS) - .0025(CS)2 accounted for 41% of the variation in Mcal ME for maintenance/LW.75. Condition score was more closely related to carcass composition in mature cows than was LW or WTHT and cows in either a thin (CS = 3) condition or a fat (CS = 7) condition required less (4.4% and 8.9%) Mcal ME/LW.75 for maintenance than cows in moderate (CS = 5) condition.

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The feedlot records of 2,111 purebred and crossbred pigs representing all purebred and all possible two-way crosses of Duroc, Hampshire and Yorkshire were analyzed to evaluate average daily gain on test, age at 100 kg, average backfat probe of gilts, average daily feed consumption and feed conversion. A random sample of 392 barrows was used to evaluate carcass traits. The data were analyzed to determine breed of sire and breed of dam effects, to evaluate differences between reciprocal crosses and to estimate heterosis. Breed of sire and breed of dam effects were significant for many of the traits evaluated. Straightbred Durocs had a higher average daily gain, were fatter and produced carcasses that were firmer and had more marbling than straightbred Hampshires or Yorkshires (P<.05). Yorkshires were the most efficient straightbred while Hampshires had the largest longissimus muscle areas and leanest carcasses of the straightbreds. Significant differences were noted between reciprocal crosses. When Yorkshires were involved in the cross, the pigs were more efficient, consumed less feed per day and produced carcasses that were leaner and had larger longissimus muscle areas when the Yorkshire was used as the dam rather than as the sire (P<.05). Significant and favorable heterosis was found for average daily gain, age at 100 kg, feed efficiency, feed consumption and carcass length ~Journal Article 3000 of the Agricultural Experiment Station,

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