Abstract
The objective of this study was to estimate genetic and phenotypic correlations of body weight at 6 weeks of age (BW6), as well as final carcass yield, and moisture, protein, fat and ash contents, using data from 3,422 F2 chickens originated from reciprocal cross between a broiler and a layer line. Variance components were estimated by the REML method, using animal models for evaluating random additive genetic and fixed contemporary group (sex, hatch and genetic group) effects. The heritability estimates (h2) for BW6, carcass yield and percentage of carcass moisture were 0.31 ± 0.07, 0.20 ± 0.05 and 0.33 ± 0.07, respectively. The h2 for the percentages of protein, fat and ash on a dry matter basis were 0.48 ± 0.09, 0.55 ± 0.10 and 0.36 ± 0.08, respectively. BW6 had a positive genetic correlation with fat percentage in the carcass, but a negative one with protein and ash contents. Carcass yield, thus, appears to have only low genetic association with carcass composition traits. The genetic correlations observed between traits, measured on a dry matter basis, indicated that selection for carcass protein content may favor higher ash content and a lower percentage of carcass fat.
Highlights
Great progress has been made in broiler production over the past few decades, and about 85 to 90% of the increase in productivity is attributed to genetics (Chambers, 1995)
Quantitative trait locus (QTL) mapping is the first stage in identifying chromosomal regions involved in the genetic control of traits that are economically important for the chicken industry
The lower mean body-weight at 6 weeks (Table 1) was expected, when compared to the results reported for pure broiler lines, with means ranging from 1.7 to 2.3 kg (Schmidt et al, 2003), and for chickens from a cross between a high-reproductive female line and a high-growth male line, as reported by Zerehdaran et al, (2004), who studied live weights at 49 days of age
Summary
Great progress has been made in broiler production over the past few decades, and about 85 to 90% of the increase in productivity is attributed to genetics (Chambers, 1995). Even though difficult and costly (Ikeobi et al, 2002; Lagarrigue et al, 2006), phenotype-based selection methods for reducing fat deposition have improved carcass composition by reducing overall fatness. Though this has been in detriment of meatquality (Nadaf et al, 2007). Quantitative trait locus (QTL) mapping is a method that has been used successfully to examine genetic contributions to certain quantitative traits, by correlating allelic variation in polymorphic genetic markers with trait variability (Tercic et al, 2009).The identification of markers linked to genomic regions that regulate economically important traits could be useful in marker assisted selection. The genetic correlations between traits can provide information on how much genetic overlap exists between traits, and support QTL findings (Nones et al, 2005)
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