EFFECTS OF BREED AND RETAINED HETEROSIS ON MILK-YIELD AND 200-DAY WEIGHT IN ADVANCED GENERATIONS OF COMPOSITE POPULATIONS OF BEEF-CATTLE

Retained heterosis in F2 cows nursing F3 progeny was evaluated in 3-, 4-, and greater-than-or-equal-to 5-yr-old cows. Traits evaluated included milk yield at three stages of lactation and 200-d weight of progeny. Breed effects were evaluated in the nine parental breeds (Red Poll [R] Hereford [H], Angus [A], Limousin [L], Braunvieh [B], Pinzgauer [P], Gelbvieh [G], Simmental [S], and Charolais [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, 1/4 A). Breed effects were significant for 12-h milk yield, estimated 200-d milk yield, and 200-d weight of progeny. Herefords were lowest (P < .05) for 12-h milk yield and estimated 200-d milk yield, and Braunvieh produced significantly more milk than all breed groups except Pinzgauer and Simmental, for which the difference approached significance. The correlation among breed group means (nine parental breeds and three composites) for 12-h milk yield with 200-d weight of progeny was .91. When 200-d weight was adjusted to a common estimated 200-d milk yield, Hereford, Angus, Red Poll, and Limousin did not differ (P > .05); all were significantly lighter than Braunvieh, Pinzgauer, Gelbvieh, Simmental, and Charolais, which did not differ (P > .05) from each other. Average effect of retained heterosis for all composites on 12-h milk yield was .689 kg (14.5%) and on 200-d weight was 15.2 kg (6.9%) (P < .01). Adjusting 200-d weight of progeny to a common estimated 200-d milk yield resulted in mean retained heterosis of all composites of 6.6 kg (3.0%) (P < .05), suggesting that approximately 56% of the retained heterosis effects observed for 200-d weight of progeny was accounted for through retained heterosis effects on milk yield.