Abstract
The objective was to study alternative models for genetic analyses of carcass traits assessed by ultrasonography in Guzerá cattle. Data from 947 measurements (655 animals) of Rib-eye area (REA), rump fat thickness (RFT) and backfat thickness (BFT) were used. Finite polygenic models (FPM), infinitesimal polygenic models (IPM) and FPM combined with IPM (IPM + FPM) were empirically tested, adjusting for the effects of permanent environment, age and weight at measurement and the contemporary group. A Bayesian analysis using the computer package FlexQTLTM was adopted. The combined model adjusted to the data, allowing reliable genetic analyses of REA and BFT. For the RFT, the IPM model was the only one to have convergence and, in this case, the trait should be analyzed by a polygenic model. The presence of up to three major genes (MGs) controlling the expression of REA and two MGs for BFT was detected. The additive genetic action was over dominance to REA, and for BFT the dominance genetic action was greater. Heritability estimates, and respective standard error, adjusted for the combined model to REA were 0.15 (0.00025) for the polygenic fraction and 0.10 (0.00019) for the oligogenic fraction; for BFT was 0.19 (0.00027) and 0.13 (0.00025), respectively. Heritability of 0.17 (0.00028) was estimated for RFT when the model was adjusted to IPM. There are major genes segregating within the population studied for REA and BFT traits, thus, their genetic analyses must be studied considering oligogenic effects. The major gene effects detected for a small number of genes, may possibly help to increase the reliability in detecting chromosomal regions that explain and control the phenotypic expression of these traits, facilitating research on detection and validation of molecular markers in this population.
Highlights
The Guzerá breed has excelled in the Brazilian cattle production scenario adding significant gains in productivity, hardiness, precocity and ability to produce good quality meat
The major gene effects detected for a small number of genes, may possibly help to increase the reliability in detecting chromosomal regions that explain and control the phenotypic expression of these traits, facilitating research on detection and validation of molecular markers in this population
The phenotypic means for rib-eye area (REA), rump fat thickness (RFT) and backfat thickness (BFT) were 58.17 cm2, 2.36 mm and 3.36 mm, respectively
Summary
The Guzerá breed has excelled in the Brazilian cattle production scenario adding significant gains in productivity, hardiness, precocity and ability to produce good quality meat. Quantitative traits such as rib-eye area, rump fat thickness, and backfat thickness have been evaluated in animal breeding programs because they are correlated with several factors related to finish quality, productivity and carcass meat cut yields (Bergen, Miller, & Wilton, 2005; Lima Neto et al, 2009). The number and effects of genes controlling the phenotypic expression, gene action and genetic parameters are examples of this knowledge Such studies are scarce, especially for Bos indicus breeds such as the Guzerá. A model that combines the finite and infinitesimal polygenic effects was proposed (Bink, Uimari, Sillanpää, Janss, & Jansen, 2002; Gonçalves, Oliveira, Bovenhuis, Bink, & Van Arendonk, 2005), which allows separating the polygenic from the major gene effect over the www.ccsenet.org/jas
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