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Phenotypic Definition Influences Genetic Inference and Predictive Ability for Reining Performance in Quarter Horses
Mário Luiz Santana1, Annaiza Braga Bignardi1
1Grupo de Melhoramento Animal de Mato Grosso (GMAT), Instituto de Ciências Agrárias e Tecnológicas, Universidade Federal de Rondonópolis (UFR), Av. dos Estudantes, 5055, Cidade Universitária, Rondonópolis, Mato Grosso, Brazil.
Animal Science Journal = Nihon Chikusan Gakkaiho
|July 23, 2026
Summary
Genetic parameters for reining performance in Brazilian Quarter Horses were estimated using random regression models. Alternative phenotypic definitions, Blom-transformed rank (BLOM) and within-group rank (RANK), were compared for genetic inference and predictive ability.
Area of Science:
- Animal Genetics
- Quantitative Genetics
- Equine Science
Background:
- Reining performance evaluation is complex due to subjective scoring and competition structure.
- Accurate genetic parameter estimation is crucial for effective breeding programs in Brazilian Quarter Horses.
Purpose of the Study:
- To estimate genetic parameters for reining performance in Brazilian Quarter Horses.
- To compare the impact of two phenotypic definitions (RANK and BLOM) on genetic inference and predictive ability using random regression models.
Main Methods:
- Utilized a dataset of 21,165 longitudinal reining records from 1,603 Brazilian Quarter Horses.
- Employed random regression models (RRM), specifically cubic RRM, for genetic analysis.
- Compared within-group rank (RANK) and Blom-transformed rank (BLOM) as phenotypic definitions.
Main Results:
- Heritability estimates for reining performance were low and age-dependent, varying from 0.01–0.17 (RANK) and 0.06–0.23 (BLOM).
- Substantial phenotypic variance was attributed to permanent environmental and rider effects.
- BLOM demonstrated better predictive performance and stronger favorable genetic trends compared to RANK, while RANK showed higher additive genetic stability.
Conclusions:
- Both RANK and BLOM are valuable and complementary phenotypes for the genetic evaluation of reining performance.
- BLOM offers modest advantages in several criteria, including predictive ability and genetic trend estimation.
- RANK effectively captures relative competitive performance on the observed scale, retaining relevant information for selection.
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