Genetic parameter estimation of novel international show-jumping indicators in horses.

Genetic evaluation of show-jumping horses using international competition data reveals that certain performance measures, especially composite ratios within specific height categories, have significant heritability and can serve as useful indicators for selective breeding.

Research Objective and Importance

• To improve the genetic selection of show-jumping horses by identifying measurable and heritable traits linked to performance in international competitions.
• The ultimate breeding goal is to produce horses that consistently perform well by clearing difficult jumping courses at maximum heights, leading to better placement results.
• Current challenges include the heterogeneous nature of competition outcomes, making it difficult to pinpoint which traits are most suitable for breeding decisions.

Study Design and Data

• Data were collected from Fédération Équestre Internationale (FEI) competition records involving 19,232 horses along with their pedigree information.
• Phenotypes analyzed included:
• Traditional traits: maximum height jumped during a career, total prize money won, and number of competitions the horse participated in.
• Composite ratios: clear-round ratio (proportion of rounds cleared without faults) and placement ratio (proportion of competitions where the horse placed).
• Composite ratios were evaluated both over the entire career and within specific 5-cm FEI height categories ranging from 1.20 m to 1.60 m.

Genetic Models and Analytic Methods

• Animal models and binomial threshold models were implemented using the ASReml software to estimate genetic parameters.
• Key genetic parameters estimated included:
• Heritability (h²): the proportion of phenotypic variance attributable to genetic variance.
• Repeatability: how consistent a trait is across repeated measures on the same individual.
• Genetic correlations: the degree to which genetic factors affecting one trait also affect another trait or the same trait across categories.

Key Findings: Heritability and Repeatability

• Maximum height achieved throughout a horse’s career had moderate heritability (h² ≈ 0.22), indicating a meaningful genetic component that can be acted upon by breeding.
• Total earnings and number of competitions exhibited low heritability and modest repeatability, suggesting these are less reliable for genetic selection.
• Composite ratios analyzed over an entire career showed low heritability (observed h² ranging from 0.02 to 0.08) but moderate repeatability.
• When composite ratios were analyzed within narrower height categories, especially mid-level classes (1.35–1.45 m), heritability substantially increased (up to h² ≈ 0.59), indicating these specific sub-traits are strongly influenced by genetics.

Genetic Correlations and Implications

• High genetic correlations existed between adjacent height categories, implying similar genetic factors influence performance in neighboring competition heights.
• However, genetic correlations were weaker between the lowest and elite height levels, suggesting different genetic determinants influence performance across broader height ranges.
• This pattern indicates the need to tailor genetic evaluation and breeding strategies according to specific height categories rather than using general measures across all classes.

Conclusions and Recommendations for Breeding Programs

• FEI-restricted composite phenotypes, particularly performance ratios within mid-height competition categories, provide informative, heritable, and repeatable indicators suitable for incorporating into genetic evaluations.
• Traditional traits such as maximum height jumped can still be valuable due to moderate heritability but using height-class-specific composite ratios improves accuracy of genetic predictions.
• Selective breeding programs should consider these findings to optimize genetic progress, focusing on traits with higher heritability within relevant competition classes.
• These insights help overcome difficulties posed by the heterogeneous nature of show-jumping outcomes and enable better identification of horses with superior genetic potential for international show-jumping success.