Genome Wide Association Study for Heat Stress Mortality in a White Egg Layer Line

Heat stress is a serious hazard for poultry production in tropical and sub-topical countries but it is expected to spread more widely with global climate change. Iowa experienced an acute heat wave in summer 2012 which led to production losses and increased mortality in birds. In this study, the proportion of daughters that died from heat was calculated for 118 sire families of a white egg layer line. The number of daughters per sire ranged from 25 to 111 and averaged 68. Average mortality due to heat stress was 8.2%, ranging from 0 to 24.6%. All sires were genotyped using a 650K Affymetrix chip. After very stringent quality criteria (clustering quality, parentage, missing genotypes, MAF) 113,344 SNPs were retained for the analysis. A BayesB method was applied with a π value equal to 0.999, chosen so the number of markers fitted did not exceed the number of observations. Markers explained 8% of phenotypic variance. One 1Mb window on chromosome 5 explained 1.2% of genetic variance. If the number of daughters was fitted as weights in the analysis, the proportion of variance explained by markers dropped to 1%, but nine 1 Mb windows explained more than 1% of genetic variance on chromosomes 5 (the same top window as in the unweighted analysis), 1, 3, 18, 9 and 17. Several genomic regions potentially associated with heat stress resistance were identified some of which overlap with previously reported QTL regions on immune response.