title: Quantitative trait loci identified for blood chemistry components of an advanced intercross line of chickens under heat stress.
abstract: BACKGROUND
  Heat stress in poultry results in considerable economic losses and is a concern for both animal health and welfare. Physiological changes occur during periods of heat stress, including changes in blood chemistry components. A highly advanced intercross line, created from a broiler (heat susceptible) by Fayoumi (heat resistant) cross, was exposed to daily heat cycles for seven days starting at 22 days of age. Blood components measured pre-heat treatment and on the seventh day of heat treatment included pH, pCO2, pO2, base excess, HCO3, TCO2, K, Na, ionized Ca, hematocrit, hemoglobin, sO2, and glucose. A genome-wide association study (GWAS) for these traits and their calculated changes was conducted to identify quantitative trait loci (QTL) using a 600 K SNP panel.
  
  
  RESULTS
  There were significant increases in pH, base excess, HCO3, TCO2, ionized Ca, hematocrit, hemoglobin, and sO2, and significant decreases in pCO2 and glucose after 7 days of heat treatment. Heritabilities ranged from 0.01-0.21 for pre-heat measurements, 0.01-0.23 for measurements taken during heat, and 0.00-0.10 for the calculated change due to heat treatment. All blood components were highly correlated within measurement days, but not correlated between measurement days. The GWAS revealed 61 QTL for all traits, located on GGA (Gallus gallus chromosome) 1, 3, 6, 9, 10, 12-14, 17, 18, 21-28, and Z. A functional analysis of the genes in these QTL regions identified the Angiopoietin pathway as significant. The QTL that co-localized for three or more traits were on GGA10, 22, 26, 28, and Z and revealed candidate genes for birds' response to heat stress.
  
  
  CONCLUSIONS
  The results of this study contribute to our knowledge of levels and heritabilities of several blood components of chickens under thermoneutral and heat stress conditions. Most components responded to heat treatment. Mapped QTL may serve as markers for genomic selection to enhance heat tolerance in poultry. The Angiopoietin pathway is likely involved in the response to heat stress in chickens. Several candidate genes were identified, giving additional insight into potential mechanisms of physiologic response to high ambient temperatures.
authors.affiliation: Department of Animal Science, Iowa State University, Ames, IA, USA.
authors.forename: Angelica
authors.initials: A
authors.lastname: Van Goor
authors.affiliation: Department of Poultry Science, North Carolina State University, Raleigh, NC, USA.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Ashwell
authors.affiliation: Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Persia
authors.affiliation: Department of Animal Science, Iowa State University, Ames, IA, USA.
authors.forename: Max F
authors.initials: MF
authors.lastname: Rothschild
authors.affiliation: Department of Animal and Food Sciences, University of Delaware, Newark, DE, USA.
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Schmidt
authors.affiliation: Department of Animal Science, Iowa State University, Ames, IA, USA. sjlamont@iastate.edu.
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Lamont
mesh_terms: D042682:Angiopoietins / Q000235:genetics; D000818:Animals; D001774:Blood Chemical Analysis; D002645:Chickens / Q000097:blood / Q000235:genetics*; D003433:Crosses, Genetic; D055106:Genome-Wide Association Study; D005838:Genotype; D018869:Heat-Shock Response / Q000235:genetics*; D006358:Hot Temperature; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide; D040641:Quantitative Trait Loci
chemical_list: D042682:Angiopoietins