0ver,2000 records wereManalyzed from a trial at Goudies Station to evaluate direct (h1) and maternal (hM0) heterosis, and seven components defined below, for birth date and live weights up to the yearling stage. The Angus (A) and Hereford (H) breeds were represented as straightbreds, FI, F2 and F3 crosses and first backcrosses using both FI sires and FI dams. Means of breeds and crosses (17 mating types) were evaluated by least squares, fixed-model procedures, and then the mating type effects were replaced by seven multiple regression coefficients (Koch et al., 1985) to estimate average individual (g1), average maternal (g ) and average maternal granddam (g ) genetic effects, individual (d1) and maternal (dj dominance effects and corresponding (gg1 and gg ) two-locus additive x additive epistatic effects. A paternal dominance effect was not estimable because of linear dependence. Breed and crossbred means were as expected for A and H; the birth-date-adjusted live weights favoured H (compared with unadjusted data) because of a later birth date in straightbred and FI calves out of H dams. Heterosis (h1 and lr^ effects were significant and positive for all traits, except h1 for birth date. For age-adjusted weaning andM yearling weights, h1 values were 4.5+1.3 kg (3.1%) and 13.2+1.5 kg (5.9%); In 0 values were 10.9+1.4 kg (7.4%lgand 4.2+1.7 kg (1.9%). For,,weaning weight and preweaning gain, the g* and g b effects were negative and g positive for Angus, as also found by Koch et al. (1985). The epistatic effects were non-significant, but had large sampTTng errors. The F3s showed an advantage over straightbred performance for weaning but not yearling weight.

C. A Morris, R. L Baker, W. D Hohenboken, D. L Johnson, N. G Cullen

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume IX. Breeding programs for dairy and beef cattle, water buffalo, sheep, and goats., , 301–307, 1986
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