DIFFERENCES IN CARCASS TRAITS OF THREE BREEDS OF SWINE AND CROSSES AT FIVE STAGES OF DEVELOPMENT

Carcass measurements from 249 pigs representing all possible two-breed crosses of Minnesota No. 1 (M), Pietrain (P), and Yorkshire (Y) breeds were recorded following slaughter at five developmental stages (35 days of age, 22.5 kg, 45.0 kg, 67.5 kg, and 90.0 kg liveweight). The objectives were to determine how advancing maturity affected reciprocal differences and heterosis, to examine breed differences, and to calculate growth curves for these measurements. Three distinct patterns were observed for reciprocal differences. The first was an increase in magnitude, the second parabolic, and the third a decrease in magnitude. Statistically significant heterosis estimates were too few to allow for an examination of trends associated with advancing maturity. The following breed differences were found: (M = Y)>P for carcass length, M>(P = Y) for mean backfat thickness, P>Y>M for loin eye area, ham weight, boned ham weight, semitendinosus weight, biceps femoris weight, and semimembranosus weight, (P = Y)>M for loin weight, shoulder weight, biceps brachii weights, femur weight, and ham and loin percentage, and Y>(M = P) for humerus weight. The growth curves indicated that 80% of total carcass length was achieved by 45.0 kg, mean backfat thickness, loin eye area, femur weight, and humerus weight had 80% of their growth completed by 67.5 kg, and boned ham weight, loin weight, shoulder weight, biceps brachii weight, ham weight, semitendinosus weight, semimembranosus weight, and biceps femoris increased directly proportional to liveweight. Key words: Reciprocal differences, heterosis, breed differences, carcass, growth curves, pigs