Resumen

THEUNISSEN, A.; SCHOLTZ, M.M.; NESER, F.W.C.  y  MACNEIL, M.D.. Crossbreeding to increase beef production: Additive and non-additive effects on fitness traits. S. Afr. j. anim. sci. [online]. 2014, vol.44, n.4, pp.335-349. ISSN 2221-4062.  http://dx.doi.org/10.4314/sajas.v44i4.3.

Fitness is of paramount importance to efficient and profitable beef production. Thus, the objective of this study was to estimate genetic components of fitness traits measured in Afrikaner (A), Brahman (B), Charolais (C), Hereford (H) and Simmentaler (S). For this study, the fitness traits recorded were percentage of cows exposed that were subsequently certified pregnant (PR), percentage of certified pregnant cows that subsequently calved (CR), percentage of calves born that survived to weaning (SV) and the percentage of cows exposed that ultimately weaned a calf (WR). Data were mean performance of straightbred, F1 cross, backcross and three-breed cross females. All crossbred females were of at least 25% A heritage. Breed group means were equated with their genetic expectations assuming recombination effects were nil and the heterosis effects were proportional to the expected heterozygosity in the crosses relative to the purebreds. With the exception of B-sired females from CA cross dams, the genetic model fit the breed group means with a high degree of fidelity. Breed-specific genetic effects tended not to individually exceed the magnitude of their standard errors. However, when the breed-specific genetic effects were combined to predict breed group means, the fitness of crossbred females, on average, exceeded that of their straightbred contemporaries. No particular advantage was noted for adding Brahman to the breed composition of crossbred females with at least 25% Afrikaner heritage. In summary, these data are viewed as being supportive of the use of breed resources in organized crossbreeding systems, such as two- and three-breed rotations that maintain at least 25% Afrikaner germplasm in the breeding females.

Palabras clave : Afrikaner cattle genotypes; heterosis effects; predicted phenotypic values; weaning rate.

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