BREED EFFECTS, RETAINED HETEROSIS, AND ESTIMATES OF GENETIC AND PHENOTYPIC PARAMETERS FOR CARCASS AND MEAT TRAITS OF BEEF-CATTLE

Retained heterosis for meat traits was estimated in F-3 generation cas trate males in three composite populations of beef cattle finished on two levels of dietary energy density (2.82) Mcal of ME and 3.07 Mcal o f ME and 11.50% CP) and serially slaughtered at four end points at int ervals of 20 to 22 d. Breed effects were evaluated in nine parental br eeds (Red Poll [R], Hereford [H], Angus [A], Limousin [L], Braunvieh [ B], Pinzgauer [P], Gelbvieh [G], Simmental [S], and Charolais [C]) tha t contributed to the three composite populations (MARC I = 1/4 B, 1/4 C, 1/4 L, 1/8 H, 1/8 A; MARC II = 1/4 G, 1/4 S, 1/4 H, 1/4 A; and MARC III = 1/4 R, 1/4 P, 1/4 H, and 1/4 A). Breed effects were important ( P < .01) for all carcass and meat traits evaluated. Dietary energy den sity and slaughter group affected (P < .05) most traits evaluated. The effects of retained heterosis were not consistent among composites. F or the mean of the three composites, retained heterosis was significan t. only for percentage of 9-10-11th rib fat and for percentage of reta il product. Phenotypic correlations indicated that marbling score was a poor predictor of palatabiltiy attributes of individual carcasses. E stimates mates of heritability were intermediate to high for measures of fatness but were generally low for palatability attributes. The hig h negative genetic correlation (-.56) between percentage of retail pro duct and marbling score and the relatively low genetic correlations be tween percentage of retail product and palatability attributes suggest s the need for simultaneous attention to percentage of retail product and palatability attributes rather than to marbling score. Correlation s among breed group means were generally high for measures of fatness with palatability attributes and were high and negative for percentage of retail product with marbling score and with other measures of fatn ess. Limited opportunity exists for selecting among breeds to achieve high levels of marbling in the longissimus muscle simultaneously with a high percentage of retail product. These results suggest that the mo st logical approach to resolution of the genetic antagonism between fa vorable carcass composition and less favorable palatability attributes is to form composite breeds with breed contributions organized to ach ieve an optimum balance between favorable carcass composition and desi rable palatability attributes at optimum slaughter weights.