Genetic parameters for blood oxygen saturation, body weight and breast conformation in 4 meat-type chicken lines.

Roslin Institute, Roslin, Midlothian EH25 9PS, Scotland, UK.
British Poultry Science (Impact Factor: 0.94). 02/2007; 47(6):659-70. DOI: 10.1080/00071660601042372
Source: PubMed


1. The objective of the study was to explore the genetic architecture of blood oxygen saturation (SaO) (an indicator trait, negatively correlated with ascites susceptibility), body weight (Weight) and fleshing score (Flesh, a measure of breast conformation) for 4 meat-type chicken lines reared in commercial conditions. 2. Genetic components, including heritabilities and genetic correlations, were estimated by Restricted Maximum likelihood for these traits measured at 6 weeks of age. 3. Data were collected over eight generations of selection and pedigrees comprised in excess of 130,000 birds. 4. Univariate analyses were performed to allow model definition and to obtain starting values for trivariate analyses. The basic model included a random animal effect and, in further models explored, a maternal environmental effect or a genetic maternal effect or both were fitted. Models were compared using likelihood ratio tests. 5. Estimated heritabilities for SaO ranged from 0.1 to 0.2, and there was no evidence of genetic maternal effects for SaO. The environmental maternal component was significant for one of the populations only. Estimated heritabilities for both Weight and Flesh were between 0.2 and 0.4, and there was evidence of environmental and genetic maternal effects for these traits in all populations. 6. Genetic correlations between SaO and Weight and between SaO and Flesh were low and negative. This suggests that, in principle, genetic selection to simultaneously increase SaO, and therefore decrease ascites susceptibility, and WEight and Flesh could be performed using traditional (marker-free) selection methods. We discuss how a putative interaction between ascites and production traits could jeopardise the success of such methods.

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Available from: Pau Navarro, Jul 07, 2014
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    ABSTRACT: 1. Blood oxygen saturation (SaO) is a potential indicator trait for resistance to ascites in chickens. 2. The objective of the study was to investigate the genetic architecture of SaO in a meat-type chicken line reared in commercial conditions. 3. Data were collected over 15 generations of selection and were divided into two data sets on the basis of a change in recording age from 6 to 5 weeks of age, approximately halfway through the period. The resulting pedigrees comprised in excess of 90,000 birds each and, on average, 12% of these birds had SaO records. 4. Segregation analyses of SaO were carried out assuming a mixed inheritance model that included a major locus segregating in a polygenic background. 5. The analyses suggest that a major gene is involved in the genetic control of SaO in this line. The putative gene acts in a dominant fashion and has an additive effect of around 0.90 sigma(p), equivalent to a predicted difference in SaO between the two homozygous classes of more than 10%. The frequency of the allele that increases SaO changed from 0.53 to 0.65 from the first to the second set of data, consistent with selection on SaO scores. 6. Using estimated genotype probabilities at the putative major locus, we inferred that it acts in an overdominant fashion on body weight and fleshing score. If the low SaO allele leads to susceptibility to ascites, its combined effects are consistent with it being maintained in the population by a balance of natural selection on fitness nad artificial selection on growth and carcase traits. 7. Even with selection on both SaO and growth traits, the combined genotypic effects would make it difficult to remove the unfavourable low-SaO allele by means of traditional selection without the use of genetic markers.
    British Poultry Science 02/2007; 47(6):671-84. DOI:10.1080/00071660601077931 · 0.94 Impact Factor
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    ABSTRACT: In this study the effect of artificial selection on BLUP EBV for production traits on the allele frequencies of a pleiotropic QTL affecting both production and disease susceptibility was investigated. Stochastic simulations were used to model artificial selection on a production trait that is controlled, in part, by a biallelic QTL that also controls susceptibility to disease. The QTL allele increasing production also increased susceptibility to disease. Different modes of action and proportions of variation accounted for by the QTL were assessed for the production trait. The main results indicated that alleles that confer susceptibility to the disease could be maintained in the population over a long period, depending on the mode of action of the QTL. In addition, the results of the study indicate that, under various conditions, it is possible to find pleiotropic QTL that control 2 traits despite these traits appearing to be uncorrelated. Therefore, in practice, an estimate of the genetic correlation between 2 traits may be misleading when the presence of such a QTL exists. The results of this study have implications for breeding programs. For example, if a pleiotropic QTL exists that favors heterozygotes for a production trait, it would be very difficult to remove disease susceptibility alleles via traditional selection methods.
    Journal of Animal Science 12/2008; 87(3):850-9. DOI:10.2527/jas.2008-1099 · 2.11 Impact Factor
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    ABSTRACT: Ascites, also called pulmonary hypertension syndrome, is a metabolic disorder in chickens that have an insufficient pulmonary vascular capacity. The tendency of broilers to develop ascites is heritable, and successful selection against this susceptibility would benefit from good and easy-to-measure indicator traits. Blood gas parameters have been suggested as indicator traits for ascites susceptibility. Therefore, the aim of the present study was to estimate the heritability of blood gas parameters and the genetic and phenotypic correlations between blood gas parameters, heart ratio (postmortem indicator for ascites), and BW at 2 different ages. For this purpose, blood gas parameters, including the partial pressure of carbon dioxide in venous blood (pvCO(2)), the partial pressure of oxygen in venous blood (pvO(2)), and blood oxygen saturation, were measured at an average age of 22 d in nearly 3,000 broilers. To challenge the resistance of the birds to ascites, they were kept under cold conditions. Heritability for heart ratio was 0.43, and the heritability estimates were low: 0.02 for pvCO(2), 0.03 for pvO(2), and 0.07 for blood oxygen saturation. The estimated heritability for pH was 0.15, for bicarbonate was 0.19, and for total carbon dioxide content was 0.19. The genetic correlations between heart ratio and total carbon dioxide content (0.31 +/- 0.15) and between heart ratio and bicarbonate (0.31 +/- 0.15) were moderate and positive. For pvO(2), the genetic correlation with heart ratio was stronger and negative (-0.62 +/- 0.21); however, this correlation could not be estimated accurately because of the low heritability of pvO(2). For pvCO(2), the genetic correlation with the heart ratio was close to zero (-0.04 +/- 0.45). Phenotypic correlations between traits were, in general, similar to the genetic correlations. Heritabilities for blood gas parameters and the genetic correlations between blood gas parameters and the heart ratio estimated in the present study do not support the suggestion that blood gas parameters measured during wk 3 or 4 are useful traits to select against the susceptibility for ascites.
    Poultry Science 04/2009; 88(3):483-90. DOI:10.3382/ps.2008-00347 · 1.67 Impact Factor
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