Haplotype GWAS in swedish warmblood horses for conformation and jumping traits.

Objective Overview

• This study aimed to identify genetic regions (haplotypes) associated with important conformation and jumping traits in Swedish Warmblood horses by performing a genome-wide association study (GWAS) based on haplotypes rather than single markers.
• The research analyzed 380 young horses, assessed by expert judges, linking genetic variations to 36 performance-related traits, uncovering several significant genomic regions containing candidate genes related to body size, musculoskeletal development, and athletic ability.

Study Background

• The Swedish Warmblood is a horse breed valued for sport performance traits such as rideability, temperament, and physical conformation.
• Traits influencing sport performance are genetically complex, typically influenced by many genes with small effects.
• Understanding the genetic basis of these traits is crucial for improving breeding programs aiming to enhance sport performance in horses.

Study Design and Methods

• Phenotyping:
  • 380 young Swedish Warmblood horses were phenotyped using two evaluation methods: traditional scoring and linear evaluation systems.
  • Traits studied included 36 conformation and free jumping phenotypes such as height at withers, hoof quality, movement correctness, and specific jumping attributes (e.g., technique and distance estimation).
  • Evaluations were performed by expert judges during routine young horse tests to ensure consistent and reliable phenotype data.
• Genotyping:
  • All horses were genotyped with the Affymetrix® Axiom® Equine Genotyping Array containing 670,000 markers.
  • Haplotypes—blocks of linked genetic markers inherited together—were phased to identify about 78,000 haplotype blocks covering the equine genome.
• Statistical Analysis:
  • A single-trait linear mixed model was applied to assess associations between haplotypes and traits.
  • Models included corrections for confounding factors such as sex and evaluation date-location to reduce bias.
  • Significance thresholds were used to identify haplotype blocks strongly associated with phenotypes.

Key Findings

• Eleven haplotype blocks showed significant association with six traits:
  • Conformation: height at withers, hoof quality, correctness in movement.
  • Free jumping: technique of haunches, carefulness, and distance estimation during jumps.
• Genomic regions (±500 kb around significant haplotypes) contained:
  • 33 protein-coding genes
  • 31 long non-coding RNAs (lncRNAs)
  • One microRNA (miRNA)
• Important candidate genes located near significant haplotypes included:
  • LCORL and KHDRBS3 – associated with body size and overall growth regulation.
  • COL12A1, MYO6, FILIP1 – involved in musculoskeletal system development, muscle elasticity, and strength.

  These genes have plausible biological roles related to the observed traits.

Significance and Advantages of the Haplotype-Based GWAS Method

• Compared to single-marker GWAS, haplotype-based GWAS can capture combined effects of multiple linked variants within a genomic region, which is beneficial for studying complex traits controlled by many genes.
• This method revealed aggregated genetic effects that might be missed when evaluating single markers individually.
• Provides more detailed genetic architecture underlying sport-related traits.

Implications and Future Directions

• The study adds valuable knowledge about the genetic factors affecting important sport and conformation traits in Swedish Warmblood horses.
• Key candidate genes identified could be targets for future functional validation to confirm their roles in performance.
• The authors emphasize the need for:
  • Larger sample sizes to improve statistical power and reduce false positives.
  • Advanced objective phenotyping tools, such as digital measurement devices and motion capture, to more precisely quantify complex traits.
  • Further exploration of non-coding RNA functions implicated in the regulation of these traits.
• Improved understanding of genetic mechanisms will enhance selective breeding strategies to produce horses with superior sport performance and physical qualities.