Continuous genetic improvement of growth and conformation traits in broiler populations has coincided with an increase in defects in heart and lung function. These defects have led to an increased incidence of metabolic disorders such as ascites (AS) (or pulmonary hypertension), a functional hypoxia. The incidence of AS in well-managed flocks is low, but it nonetheless causes important economic losses to the breeding industry and is an important issue from a welfare standpoint. The aim of this thesis was to study the genetics of AS-related quantitative traits. A low blood oxygen saturation (SaO) value is a good indicator of AS susceptibility. The existence of substantial genetic (polygenic) variation for SaO was demonstrated for four meat-type chicken lines. Estimates of heritabilities for SaO ranged from 0.1 to 0.2 and additive genetic correlations with production traits were not different from zero. SaO data from one of these lines were analysed using a mixed inheritance model (i.e. including a major locus (MG) and polygenes) and the results suggested that a MG with two alleles at intermediate frequencies affected SaO. The putative MG accounted for a difference of 13% SaO between homozygotes and the decreasing allele was recessive. The MG was also estimated to have an overdominant effect on weight and fleshing score. The mode of action of the putative MG on SaO and production traits would hinder manipulation of its allele frequency without the use of molecular markers. A population was designed to map this putative MG. Power studies were performed to select a number of sires and their half-sib progeny. Sires were selected on the basis of their probability of being heterozygous at the putative MG as estimated by the segregation analysis. Regions around the three ryanodine receptor loci (RYR1, RYR2 and RYR3), which are candidate genes for AS, were chosen to perform a linkage study. No evidence of linkage of any of the regions studied with SaO, as a predictor of AS, was detected.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:659895 |
| Date | January 2003 |
| Creators | Navarro-MartÃnez, Pau |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/15495 |
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