Phenotypic and Genetic Evaluation of Morphometric and Dynamic Traits in Mangalarga Horses.

Overview

• This study investigates both genetic and phenotypic characteristics related to body measurements and movement traits in Mangalarga horses to aid objective and effective breeding selection.
• The research provides heritability estimates and genetic correlations for several key traits, offering valuable insights for improving horse breeding strategies.

Background and Objective

• The Mangalarga horse is a breed where selection traditionally relied on subjective assessments of traits, potentially biasing selection toward appearance rather than functional performance.
• Objective genetic evaluation of morphometric (body measurement) and dynamic (locomotion/movement) traits can improve selection accuracy and prevent undesirable correlated responses.
• The study aims to estimate phenotypic means, heritabilities, and genetic correlations for key morphometric and dynamic traits, thus providing breeding values to support selection decisions.

Data and Methods

• Pedigree data consisted of 212,361 Mangalarga horses born over a century (1919–2019), ensuring comprehensive genetic lineage information.
• Phenotypic measurements for:
  • Morphometric traits: 54,617 horses (1977–2019)
  • Dynamic traits: 45,010 horses (1977–2019)
• The study used Animal Models implemented with BLUPF90+ software for estimating variance components, heritability, and genetic correlations, which is a standard methodology in quantitative genetics.

Key Traits Evaluated

• Morphometric traits:
  • Withers height (height at the shoulder)
  • Thoracic perimeter (chest circumference)
  • Cannon bone perimeter (circumference of the lower leg bone)
• Dynamic traits (related to locomotion and overall movement quality):
  • Movement (general gait quality)
  • Dynamic limbs (quality and coordination of limb movements)
  • Canter (quality of the canter gait)
  • Comfort (overall riding comfort considers smoothness and balance)
  • Total dynamics (aggregate score representing overall dynamic traits)

Results: Phenotypic Means and Heritabilities

• Phenotypic averages provide baseline measurements for these traits in the Mangalarga horse, for example:
  • Withers height average: ~154 cm (±4.43 cm)
  • Thoracic perimeter average: ~179 cm (±7.97 cm)
  • Cannon bone perimeter average: ~19 cm (±0.96 cm)
• Heritability estimates show the proportion of variation due to genetics:
  • Withers height: high heritability of 0.58, meaning strong genetic control
  • Thoracic perimeter: moderate heritability of 0.40
  • Cannon bone perimeter: lower heritability of 0.21
  • Dynamic traits heritabilities ranged approximately from 0.22 (canter) to 0.34 (movement), indicating that these movement traits also have a substantial genetic basis and could respond to selection.

Genetic and Phenotypic Correlations

• Phenotypic correlations measure observable trait associations; genetic correlations measure shared genetic influences:
  • Highest phenotypic correlation was between movement and total dynamics (0.87), indicating a strong positive association in appearance/performance.
  • Lowest phenotypic correlation observed was between cannon bone perimeter and comfort (0.06), essentially negligible.
  • Genetic correlations mirrored this with a high positive value between movement and total dynamics (0.92), indicating that improving movement genetically will improve total dynamic scores.
  • The weakest genetic correlation was near zero between dynamic limbs and cannon bone perimeter (-0.01), implying independent genetic control.
  • A notable negative genetic correlation was found between movement and cannon bone perimeter (-0.21), suggesting antagonism: as movement improves genetically, cannon bone perimeter may decrease, or vice versa.

Interpretation and Implications

• Moderate to high heritabilities signal that genetic selection on these traits can result in meaningful improvement over generations.
• The negative genetic correlation between movement and cannon bone perimeter presents a breeding challenge, as increasing movement performance may inadvertently reduce bone robustness, which can affect durability and soundness.
• A balanced breeding strategy is required:
  • Selection indexes could weight dynamic traits heavily to improve gait and movement quality.
  • Minimum thresholds or constraints should be set for bone structure traits to avoid compromising bone quality.
• This study is the first to provide comprehensive breeding values for these traits in the Mangalarga breed, offering breeders objective tools to guide selection beyond subjective judgments.

Conclusions

• The research validates that key morphometric and dynamic traits are significantly heritable in Mangalarga horses.
• Genetic parameters estimated here enable the development of optimized selection indexes that balance improvements in locomotion with maintenance of good bone structure.
• Overall, the findings advance the ability to improve the Mangalarga breed’s performance and durability through scientifically informed breeding.