Unraveling the genomic architecture of hock conformation defects in Pura Raza Española horses.

Overview

• This study investigated the genetic factors behind hock conformation defects in Pura Raza Española horses to identify genomic regions linked to these abnormalities.
• The goal was to understand the hereditary nature of hock defects and provide information that could improve selective breeding practices to enhance horse health, performance, and appearance.

Background and Importance

• Conformational traits determine the shape and morphology of horses, influencing their health, athletic performance, and aesthetics.
• The hock is a critical joint in horses, and defects here can compromise functionality and increase the risk of musculoskeletal problems.
• Understanding the genomic basis of hock defects is important for horse breeders aiming to reduce these issues through genetic selection.

Study Population and Data Collection

• A large sample of 58,930 Pura Raza Española (PRE) horses was evaluated for hock angle conformation defects.
• Out of these, 4,122 horses were genotyped using either high- or medium-density DNA arrays allowing for detailed genomic analysis.
• Hock conformation was assessed in two views: lateral (LVHD) and rear (RVHD), analyzed both as continuous variables and categorized into defect types:
• Continuous evaluation: measuring the hock angle.
• Multinomial (categorical) approach: classifying defects as closed vs. open and convergent vs. divergent.

Findings on Prevalence and Heritability

• Out of the total horses, 49,386 showed deviations from optimal hock angle, indicating conformation defects.
• Approximately 10.1% exhibited severe or very severe defects.
• The most common defect was the open hock (6.67% severe or very severe cases), whereas closed hock was rare (0.2%).
• Heritability estimates indicate a genetic contribution to these traits:
• Heritability for continuous traits: 0.18 for LVHD, 0.25 for RVHD.
• Heritability for multinomial classification ranged from 0.25 to 0.42, suggesting a moderate to high genetic influence for certain defect types.

Genomic Analysis and Associations

• A weighted single-step genomic REML (restricted maximum likelihood) analysis and genome-wide association study (GWAS) were conducted to pinpoint genetic regions linked to hock defects.
• Eight genomic regions were significantly associated with hock conformation defects.
• Within these regions, 17 candidate genes were identified related to:
• Musculoskeletal diseases
• Bone malformations
• Joint disorders
• Cartilage defects
• Bone fragility
• These genes provide potential targets for understanding the molecular mechanisms behind hock defects.

Implications for Breeding and Future Research

• The identification of genetic regions and heritability of hock defects suggests selective breeding can reduce the prevalence of these defects.
• Breeding strategies informed by genetic markers can improve horse welfare by minimizing musculoskeletal problems and enhancing performance.
• The study advances knowledge of the genetic basis of equine conformation defects, offering new insights into joint and bone health.
• Further research is required to validate these findings and explore the genetic mechanisms in more detail across different horse breeds.