title: Genome-wide association study on legendre random regression coefficients for the growth and feed intake trajectory on Duroc Boars.
abstract: BACKGROUND
  Feed intake and growth are economically important traits in swine production. Previous genome wide association studies (GWAS) have utilized average daily gain or daily feed intake to identify regions that impact growth and feed intake across time. The use of longitudinal models in GWAS studies, such as random regression, allows for SNPs having a heterogeneous effect across the trajectory to be characterized. The objective of this study is therefore to conduct a single step GWAS (ssGWAS) on the animal polynomial coefficients for feed intake and growth.
  
  
  RESULTS
  Corrected daily feed intake (DFI Adj) and average daily weight measurements (DBW Avg) on 8981 (n=525,240 observations) and 5643 (n=283,607 observations) animals were utilized in a random regression model using Legendre polynomials (order=2) and a relationship matrix that included genotyped and un-genotyped animals. A ssGWAS was conducted on the animal polynomials coefficients (intercept, linear and quadratic) for animals with genotypes (DFIAdj: n=855; DBWAvg: n=590). Regions were characterized based on the variance of 10-SNP sliding windows GEBV (WGEBV). A bootstrap analysis (n=1000) was conducted to declare significance. Heritability estimates for the traits trajectory ranged from 0.34-0.52 to 0.07-0.23 for DBWAvg and DFIAdj, respectively. Genetic correlations across age classes were large and positive for both DBWAvg and DFIAdj, albeit age classes at the beginning had a small to moderate genetic correlation with age classes towards the end of the trajectory for both traits. The WGEBV variance explained by significant regions (P<0.001) for each polynomial coefficient ranged from 0.2-0.9 to 0.3-1.01% for DBWAvg and DFIAdj, respectively. The WGEBV variance explained by significant regions for the trajectory was 1.54 and 1.95% for DBWAvg and DFIAdj. Both traits identified candidate genes with functions related to metabolite and energy homeostasis, glucose and insulin signaling and behavior.
  
  
  CONCLUSIONS
  We have identified regions of the genome that have an impact on the intercept, linear and quadratic terms for DBWAvg and DFIAdj. These results provide preliminary evidence that individual growth and feed intake trajectories are impacted by different regions of the genome at different times.
authors.affiliation: Department of Animal Science, North Carolina State University, Raleigh, NC, 27695-7627, USA. jthoward@ncsu.edu.
authors.forename: Jeremy T
authors.initials: JT
authors.lastname: Howard
authors.affiliation: Department of Animal Science, North Carolina State University, Raleigh, NC, 27695-7627, USA. sjiao@ncsu.edu.
authors.forename: Shihui
authors.initials: S
authors.lastname: Jiao
authors.affiliation: Department of Animal Science, North Carolina State University, Raleigh, NC, 27695-7627, USA. ftmaestr@ncsu.edu.
authors.forename: Francesco
authors.initials: F
authors.lastname: Tiezzi
authors.affiliation: Smithfield Premium Genetics, Rose Hill, NC, 28458, USA. Yijian.Huang@spgenetics.com.
authors.forename: Yijian
authors.initials: Y
authors.lastname: Huang
authors.affiliation: Smithfield Premium Genetics, Rose Hill, NC, 28458, USA. kent.gray@spgenetics.com.
authors.forename: Kent A
authors.initials: KA
authors.lastname: Gray
authors.affiliation: Department of Animal Science, North Carolina State University, Raleigh, NC, 27695-7627, USA. christian_maltecca@ncsu.edu.
authors.forename: Christian
authors.initials: C
authors.lastname: Maltecca
mesh_terms: D000818:Animals; D001835:Body Weight; D004435:Eating; D056726:Genetic Association Studies; D055106:Genome-Wide Association Study; D040641:Quantitative Trait Loci; D019655:Quantitative Trait, Heritable; D013552:Swine