BREED EFFECTS AND RETAINED HETEROSIS FOR GROWTH, CARCASS, AND MEAT TRAITS IN ADVANCED GENERATIONS OF COMPOSITE POPULATIONS OF BEEF-CATTLE

Retained heterosis for growth, carcass, and meat traits was estimated in F3 generation castrate male progeny in three composite populations finished on two levels of dietary energy density (2.82 Mcal of ME and 3.07 Mcal of ME and 11.50% CP) and serially slaughtered at four end po ints at intervals of 20 to 22 d. Breed effects were evaluated in nine parental breeds (Red Poll [R], Hereford [H], Angus [A], Limousin [L], Braunvieh [B], Pinzgauer [P], Gelbvieh [G], Simmental [S], and Charola is [C] that 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 i mportant (P < .01) for carcass weight, dressing percentage, fat thickn ess, and marbling score; for retail product, fat trim and bone percent ages and weights at two levels of fat trim (8 and 0 mm); and for carca ss lean, fat, and bone percentages and weights. Mean slaughter weight was 54.7 kg greater for the Simmental, Gelbvieh, and Charolais breeds than for the Limousin but did not differ (P > .05) from Limousin in re tail product weight or carcass lean weight because of higher dressing percentage, lower fat trim percentage, and lower bone percentage of Li mousin. The effects of dietary energy density were important (P < .01) for most traits. The interaction of breed group x dietary energy dens ity generally was not important. Retained heterosis generally was sign ificant for each composite population for weight of retail product, fa t trim, bone, and carcass lean, fat, and bone. For percentage of retai l product, fat trim, carcass lean, carcass fat, and chemical fat in th e 9-10-11th rib cut, generally, heterosis was significant for composit es MARC II and MARC III but not for composite MARC I (i.e., composites MARC II and MARC III had a lower percentage of retail product and car cass lean and a higher percentage of fat trim, carcass fat, and chemic al fat in the 9-10-11th rib cut than the mean of contributing purebred s).