Quantitative trait loci identified for blood chemistry components of an advanced intercross line of chickens under heat stress

Abstract

BackgroundHeat 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.ResultsThere 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.ConclusionsThe 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2601-x) contains supplementary material, which is available to authorized users.

Integration of genome wide association studies and whole genome sequencing provides novel insights into fat deposition in chicken

“…In order to identify the SNPs within the windows most probably linked to the QTL, we selected those with highest model frequency (Table 2 ), as adopted by Van Goor et al . 19 , 20 . The characterization of those SNPs including their effect, frequency in the population and frequency in the founder lines (TT and CC) is available in Supplementary Spreadsheet S1 .…”

“…A map file was used to position the SNPs into 943 non-overlapping windows of 1 Mb. We adopted 1 Mb non-overlapping windows in our study in agreement with other recent GWAS studies in chickens reported in the literature using genomic prediction methodology 19 , 20 , 78 , 79 . Many SNPs were fitted simultaneously in the model and due to high linkage disequilibrium, the QTL effect can be distributed across these markers 18 , and these previous studies showed that the 1 Mb windows can capture the effects.…”

“…Each window is expected to explain 0.106% of the genetic variance (100%/943) based on an infinitesimal model 20 , and windows that explained five times more than the expected value (0.53%) were considered to be biologically significant. Thus, we selected only biologically significant windows to characterize and identify PCGs.…”

Liver transcriptome response to hyperthermic stress in three distinct chicken lines

“…Van Goor et al used an AIL developed from broiler and Fayoumi to identify quantitative trait loci for body temperature, production traits and blood chemistry under heat stress [8, 18]. We compared Fayoumi in heat stress to broiler under heat stress after contrasting each line’s heat treatment group against the control group.…”

“…The 3 distinct genetic lines maintained at Iowa State University that were used in this study were a heat-susceptible broiler line, the heat-resistant Fayoumi, and the F 19 generation of a highly advanced intercross line (AIL) between the broiler and Fayoumi [8, 18]. The Fayoumi line originated from a hot climate (desert region of Egypt) and has not undergone selection for production traits.…”