Date of Award

1990

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Animal Science (Animal, Dairy, and Poultry Sciences)

First Advisor

Donald E. Franke

Abstract

Carcass measurements were taken on straightbred and crossbred steers to estimate least squares means and heterosis (1,494 steers) and, to partition additive and heterotic genetic effects (1,536 steers) on hot carcass weight (HCWT), retail yield (YIELD), ribeye area (REA), fat thickness (FT), marbling score (MS) and Warner-Bratzler shear (WBS). Steers were produced over four generations in a rotational crossbreeding study and consisted of Angus (A), Brahman (B), Charolais (C) and Hereford (H) breeds. Two-, three- and four-breed rotation systems were generated with the restriction that each breed combination include the B. Straightbreds were maintained as controls. Treatment, mating system and line within mating system were significant sources of variation for all carcass traits. Treatment effects indicated that feeding for longer periods resulted in greater HCWT, YIELD, FT and MS and lower WBS. The C was superior for yield traits, while A and H had higher FT and MS. The B was similar to A and H for yield traits and ranked last for MS and WBS. Crossbreds were superior to straightbreds for all traits except MS. Combinations involving the C had superior yield traits to other combinations. Three- and four-breed rotations had slightly heavier HCWT and YIELD than two-breed rotations. A regression model was used to partition breed direct (Ig) and maternal (Mg) additive and heterotic (Ih and Mh) genetic effects. Breed direct and maternal additive effects were expressed as deviations from $\mu$ and summed to zero. The IgC and MgC effects significantly increased yield traits. The IgA and IgH increased FT and had desirable effects on MS and WBS. The IgB effect was negative for yield traits and MS and positive (less tender) for WBS. The MgB negatively influenced all traits. Direct heterotic effects on yield traits were beneficial but not for FT and MS. The largest Ih effects were exhibited by B crosses for yield traits and WBS. Higher FT and MS were associated with the MhAB, MhBC and MhBH effects. These results confirm the importance of the C and crossbreeding involving the B for improving carcass merit of beef steers in the Gulf coast region.

Pages

137

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