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Topic:Heritability
Heritability in horses refers to the proportion of observable variation in traits among individuals that can be attributed to genetic factors. It is a key concept in understanding how traits such as height, coat color, speed, and temperament are passed from one generation to the next. Heritability estimates help in predicting the potential for selective breeding and the likelihood of certain traits being expressed in offspring. These estimates are calculated using statistical methods that analyze the resemblance between relatives. This page aggregates peer-reviewed research studies and scholarly articles that explore the genetic basis of heritable traits in horses, the methodologies for estimating heritability, and the implications for equine breeding and management practices.
Allele frequencies of 7 inherited disorders in performance and random cohorts of American Quarter Horses (2020-2024). To estimate allele frequencies for genetic diseases in the American Quarter Horse (QH), including hyperkalemic periodic paralysis (HYPP), type 1 polysaccharide storage myopathy (PSSM1), malignant hyperthermia (MH), myosin-heavy chain myopathy (MYHM), glycogen branching enzyme deficiency (GBED), hereditary equine regional dermal asthenia (HERDA), and equine juvenile spinocerebellar ataxia (EJSCA), and to compare these frequencies over time among elite performance subgroups and a random cohort of registered horses. Unassigned: In this prospective genetic survey, DNA was extracted from 300 elite ...
Inter- and intra-rater reliability of linear scoring in warmblood breeding. Reliable phenotypes are essential for successful animal breeding programmes. Subjective phenotypic assessment may lead to under- or overestimation of heritability estimates and thereby affect the power of genome-based analyses. In Warmblood horses, conformation traits are commonly assessed using linear scoring, but its reliability has not been sufficiently quantified. Objective: In this study, we investigated inter- and intra-rater reliability of linear scoring of conformation traits in German warmblood horses. Methods: Professional equine breeding experts (e.g. breeding judges) completed an o...
Implications of dominance deviations for reproductive and morphological traits in the genetic management of the Pura Raza Española horse. Dominance is a non-additive genetic effect involving allele interaction at the same locus. In animal breeding, it has often been ignored due to its complexity and the low accuracy of pedigree-based estimates. This study analysed dominance variance components for reproductive traits [age at first foaling (AFF), reproductive efficiency (RE), interval between first and second foaling (I12)] and morphological traits [scapulo-ischial length (SIL), dorsal sternal diameter (DSD), knee circumference (KC)] in Pura Raza Española (PRE) mares. The aim was to assess the magnitude of dominance effects acro...
Environmental and genetic effects on measured hock bone proportions in young Polish Warmblood horses undergoing performance test training for breeding horses. The hock bone proportions in young Polish Warmblood horses (69) were studied based on x-ray image measurements done during official breeding horse performance testing. Six measurements were used to identify 4 width and length proportion indices. The radiological examinations were done before and after horse training, which consists of work with or without the rider at walk, trot and canter (40-50min) with some light class (< 100cm) jumping (<12 jumps) 6 days a week. The training effect was investigated using analysis of variance (procedure MIXED, Statistical Analysis System). The statist...
Phenotypic Definition Influences Genetic Inference and Predictive Ability for Reining Performance in Quarter Horses Using Random Regression Models. Reining performance is influenced by subjectivity and competition structure, challenging genetic evaluation. This study estimated genetic parameters for reining performance in Brazilian Quarter Horses using random regression models (RRM) and evaluated how alternative phenotypic definitions affect genetic inference and predictive ability. A dataset comprising 21,165 longitudinal records from 1603 horses was analyzed, comparing within-group rank (RANK) and Blom-transformed rank (BLOM). Model comparison indicated that cubic RRM provided the best fit for both phenotypes. Heritability estimates wer...
Phenotypic and genetic factors that affect the likelihood of Standardbred foals achieving a race start. This study was conducted to quantify the probability of a Standardbred foal attaining early career milestones and to estimate some environmental and genetic factors that influence achievement of those milestones. Data for all Standardbred foals registered at birth in New Zealand from 1995 to 2018 were used to estimate variance components and fixed effects influencing attainment of three early-career traits; registered with trainer (REG), starting in a trial (TRIAL) and starting in a race (RACE). The study population comprised 65,256 foals. Of these, 65.5% attained REG, 55.4% progressed to TRIA...
When genes meet money: Genotype-by-prize interaction in Quarter Horses. Barrel racing performance reflects a complex interplay among genetic merit, rider ability, training strategies, and competition-specific conditions. In practice, events differ substantially in their economic scale, and prize money can serve as a proxy for management intensity, rider expertise, and selection pressure. Objective: This study investigated whether economic stratification, represented by total prize money per event, is associated with changes in (co)variance components for barrel racing time in Brazilian Quarter Horses. Methods: A reaction-norm model was implemented using 349,262 ra...
Genetic Indicators of Performance Resilience in Barrel Racing Quarter Horses. Resilience, defined as the capacity to maintain consistent performance under variable conditions, has emerged as a relevant breeding objective in livestock systems, yet remains largely unexplored in equine populations. The objectives of this study were to (1) derive indicators of resilience from longitudinal barrel racing time (BRT) records in Brazilian Quarter Horses, (2) estimate genetic parameters for these indicators, and (3) quantify their genetic relationships with BRT and accumulated career earnings (ACE). The dataset comprised BRT records from barrel racing events held between 2010 and...
Sport predispositions in warmblood horses: insights from Grand Prix competitions. The aim of this study was to pilot the assessment of sport predispositions in warmblood horse breeds, both domestic and foreign, and to evaluate factors influencing their performance. Data from 293 horses (725 starts) competing in national Grand Prix events with obstacle heights of 140-145 cm were analysed using general mixed models. The origins of Polish Halfbred Horses were examined, and correlations between results in the Young Horse Championships and later Grand Prix performance were assessed. Results showed that performance is significantly influenced by genetic factors, such as breed and...
Thermal Thresholds and Genetic Sensitivity in Barrel Racing Performance of Quarter Horses Across Temperature-Humidity Indices. Heat stress is an increasingly important challenge for the performance and welfare of equine athletes, particularly in competitions conducted across diverse climatic conditions. Understanding the genetic basis of performance responses to increasing thermal load is therefore essential to support robust genetic evaluation and sustainable selection strategies. The objective of this study was to evaluate barrel racing performance of Brazilian Quarter Horses across thermal environments defined by two widely used indicators, the temperature-humidity index (THI) and the wet bulb globe temperature (WB...
Research Trends and Emerging Frontiers in Racehorse Genetics: A Bibliometric Analysis. The global horse racing industry relies heavily on elite breeding. Therefore, a molecular understanding of athletic traits is crucial for the industry's advancement. This study utilized Bibliometrix, VOSviewer, and CiteSpace to conduct a comprehensive bibliometric analysis of 869 publications in the Web of Science Core Collection (2011-2025), decoding the academic landscape and evolutionary trajectory of equine genetics. The results indicate a significant upward trend in academic output since 2019, with the United States, South Korea, and the United Kingdom emerging as the primary contributors...
Is the walk and trot efficiency a hereditary trait in primitive Konik Polski horses? Performance testing is a critical tool for achieving genetic progress, yet its long-term effectiveness in primitive breeds under conservation programs is poorly documented. The Konik Polski horse breeding program aims to improve utility while preserving primitive characteristics. Unassigned: This retrospective study analyzed a 25-year longitudinal dataset ( = 1,608) from the official Field Performance Test to quantify genetic trends in gait efficiency, using nonparametric methods to assess the effects of test type, year, and age on stride length and speed at the walk and trot. To estimate he...
Unraveling the genomic architecture of hock conformation defects in Pura Raza Española horses. Conformational traits define a horse's shape and morphology, heavily influencing its functionality, sport performance, health, and appearance, making conformation a critical selection criterion in horse breeding. However, the genomic basis of conformational defects, specifically those affecting the hock, remains largely unexplored. This research aimed to identify the genomic regions associated with hock defects using a large cohort of Pura Raza Española (PRE) horses. A total of 58,930 horses were evaluated for hock angle, with 4,122 genotyped on high or medium density arrays. For this purpose...
Machine Learning-Based Genome-Wide Association Study Reveals Genetic Loci Associated with Body Measurement Traits in Yili Horses. Body measurement traits are key indicators for evaluating growth performance, production potential, and breeding value in Yili horses. However, studies investigating the association between body measurement traits and mutation loci in Yili horses remain limited. In this study, 255 adult Yili mares were used as the study population, including 152 speed-type and 103 meat-type individuals. Whole-genome resequencing was performed, and four phenotypic traits and body weight were measured. A mixed linear model (MLM)-based genome-wide association study (GWAS) was conducted using GEMMA (v 0.98.5), inc...
Morphometric Characterization and Preliminary Heritability Estimates of Body Measurements in the Polish Konik Populations. The objective of this paper is to demonstrate the morphometric diversity of 172 Polish Koniks from the largest Polish breeding centers and to assess their genetic diversity by estimating the effective population size () and heritabilities () of the studied traits. The animals were bred under a stable housing system. Horses of both sexes aged 3 to 24 years were analyzed. Each horse was characterized with 40 metric traits. Multifactorial analyses (PCA, DA) and the REML method were applied to reveal the exterior differentiation and the development of distinct morphometric types. The findings esta...
Deficiency in homozygous haplotypes reveals recessive lethal variants affecting fertility and viability in the Friesian horse. BACKGROUND: Recessive lethal alleles causing pre- or postnatal death in homozygous mutant animals, could lead to reduced fertility success. The Friesian horse breed has signs of reduced fertility and has faced high inbreeding rates in the past (∆F > 1%). Consequently, by genetic drift lethal alleles may have reached moderate to high frequencies in the population. Our aim was to identify lethal recessive alleles that — when homozygous — may cause pre- or postnatal death in the Friesian horse. RESULTS: We analyzed genotypes (70 K SNP) of over 8,000 Friesian horses, looking for hapl...
Fragile foal syndrome: manifestations, heterozygous advantage and the future of breeding policies. Scientific interest in relation to Fragile Foal Syndrome (FFS) has proliferated in the last decade, but before this, many clinical cases were attributed to other similarly presenting equine neonatal disorders. It was thought that FFS-affected foals were mainly miscarried throughout gestation, but recent study results suggest that often, foals are born alive and die shortly after birth. FFS is proposed to have originated as long ago as the Godolphin Arabian, but the definite derivation of the mutant allele is unconfirmed. The discovery that FFS is present in 11-30% of Warmbloods and 2-3% of Tho...
Heritability Estimates of Traits Assessed in Field Performance Tests of Polish Warmblood Mares. : Knowledge of the genetic background of evaluated traits has been the basis for genetic progress in every horse-breeding population and is essential for precise breeding and up-to-date decision-making. The study aimed to estimate the heritability coefficients for field performance traits in mares. : The research was based on 1408 evaluations of mares conducted during the years 2002-2021 in 51 training centers in Poland. The preliminary analyses of the effects, significant for the investigated traits, were obtained using analysis of variance, and these additional data are also presented (SAS p...
Genetic and phenotypic insights into thermal load and racing performance of Quarter Horses. Thermal load is a major welfare and performance concern for athletic horses, as physical exertion increases internal heat production. Although several phenotypic strategies have been developed to mitigate its effects, the genetic basis of thermal tolerance in horses remains largely unexplored. This study aimed to (1) evaluate the influence of thermal indices on the racing performance of Brazilian Quarter Horses, and (2) investigate the genetic basis of thermal tolerance through the estimation of genetic parameters across temperature gradients. We analyzed 21,857 racing-time (RT) records from 5...
Is There a Genetic Link Between Resting Infrared Thermography in Young Horses and Longevity in Jumping Competition? The objective was to evaluate the genetic relationship between the surface temperature of regions of interest, measured using infrared images of young horses and functional longevity in jumping. This relationship was assessed by comparing the temperatures measured in the offspring of two groups of sires, one favourable and one unfavourable, to longevity. The study used a specific data collection protocol on a sample of 921 young progeny, before they began competing, of 141 extreme stallions, comprising 61 favourable and 80 unfavourable sires. These stallions had been selected based on estimate...
Genetic parameter estimates of performance traits in Iranian Thoroughbred race horses using a Bayesian approach. Race performance in Thoroughbred horses is influenced by both genetic and environmental factors. Understanding their genetic architecture is essential for designing effective breeding programs. Objective: This study aimed to estimate genetic parameters and trends for key performance traits in Iranian Thoroughbred racehorses. Methods: Performance data, including race completion time (RCT), rank at the end of the competition (REC), and average speed (AS), were obtained from the Iranian Equestrian Federation (2002-2021). Pedigree data from 14,391 individuals were analyzed using CFC software. Gene...
The Role of Genetic and Environmental Factors in White Leg Markings: Prevalence and Heritability Analysis in Pura Raza Española Horses. White leg markings in horses are phenotypic traits influenced by genetic and environmental factors. This study analyzed their prevalence, symmetry, and genetic parameters in 38,825 Pura Raza Española (PRE) horses registered in the official studbook. White markings were scored using a binary (affected/unaffected) and a four-level ordinal scale. Most horses (38,341 out of 38,825; 98.8%) had at least one limb without white markings. The prevalence of white markings was higher in the hindlegs (17.9% LH; 14.5% RH) than in the forelegs (5.3% LF; 4.6% RF). Markings were most frequent above the fetlo...
Genetic inbreeding depression load for conformation defects and dressage traits in the Pura Raza Española horse. Investigate the genetic inbreeding depression load (IDL) on two dressage traits and two conformational defects in horses. Unassigned: The dataset included performance records for Walk and Points per Reprise (PPR) (N:43,838) and conformation data for Closed and Convergent hocks (N:57,949). Pedigree information spanned over 400,000 individuals. Inbreeding coefficients (F, F6, Fk) and partial inbreeding coefficient (Fij) were computed to quantify the IDL using Bayesian approach. Linear and ordinal logistic regressions were used to assess the relationship between inbreeding and phenotypic values. ...
Genome-wide association study reveals candidate loci on ECA1 and ECA9 for withers height in Friesian horses. In Friesian horses, withers height is an important trait as a minimum has been set to be eligible to the studbook. Several loci for withers height have been identified in horses. However, withers height has not been studied in the Friesian horse. Therefore, our aim was to identify loci associated with withers height in the Friesian horse population. We performed a genome-wide association study using 70 K SNP data of 2192 Friesian horses. We found ECA1 and ECA9 to be significantly associated with withers height, explaining 19.6% and 3.5% of the phenotypic variance, respectively. In other hors...
Better hoof, better horse – genetic correlations between ability to race barefoot and performance in trotting horses. Harness racing is popular in several parts of the world, and the ability to race barefoot is an important trait for success because of its effect on racing time. Barefoot racing is also discussed in terms of animal welfare because not all horses have hooves that tolerate racing without shoes. In Swedish Standardbred trotters (SB) and Swedish-Norwegian Coldblooded trotters (CB), the proportion of barefoot races and the probability to race barefoot in any given race (barefoot status) have low-to-moderate heritability (h = 0.07-0.28). However, the genetic correlation between the ability to race...
Exploring the Genetic Link Between Coat Colour and Morphological Traits: The Case of Peruano de Paso Horse. The Peruano de Paso is a horse breed renowned for its smooth gait, traditionally selected based on breeders' empirical knowledge. Recently, the frequency of chestnut horses, a recessive trait, has increased substantially within the official studbook. This study evaluated whether preference for chestnut coat colour has influenced morphological traits and genetic diversity within the breed. A total of 8376 records of seven morphological traits, collected by the Peruano de Paso Breeders Association over eight years, were analysed, along with a pedigree including 41,357 individuals. Morphological ...
Phenotypic Associations Between Linearly Scored Traits and Sport Horse Auction Sales Price in Ireland. This study examines the associations between linearly scored phenotypic traits and auction sales prices of young event horses in Ireland, aiming to identify key traits influencing market value. Data from 307 horses sold at public auctions (2022-2023) were analysed using regression analysis, binary optimisation, and Principal Component Analysis (PCA). Regression identified Head-neck Connection, Quality of Legs, Walk length of Stride, and Scope as highly significant predictors of sales price ( < 0.001), with Length of Croup, Trot Elasticity, Trot Balance, and Take-off Direction also significa...
To Start or Not to Start-A Matter of Genetics in Swedish Warmblood Horses? The breeding goal of the Swedish Warmblood horse (SWB) is to produce internationally competitive horses in dressage and show jumping. In the current genetic evaluation, breeding values are estimated in multiple-trait animal models where competition performance is the target trait and results from two different young horse tests serve as indicator traits. However, preselection of horses, both for young horse tests and for competitions, is not considered in the current evaluation. The overall aim of this study was to analyse the all-or-none trait start status, in competition and in young horse t...
Genetic relationship between Neck and Limb defects in Pura Raza Española Horses. Neck and limb conformational defects can impair functionality and performance in Pura Raza Española (PRE) horses. However, their potential genetic relationship has not been previously explored. Objective: To estimate the genetic correlations between two types of neck defects (Cresty neck -CN-, Ewe neck -EN-) and twelve conformational limb defects: Forelimb (Buck knee -BUK-, Calf knee -CK-, Bench knee -BEK-, Knock knee -KK-, Splay-footed forelimb -SFF-, Pigeon-toed forelimb -PTF-), rear limb (Closed hock -CH-, Open hock -OH-, Convergent hock -CVH-, Divergent hock -DVH-, Splay-footed rear limb ...
