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.
DeBowes RM, Gaughan EM.Equine congenital dental deformities are not limited merely to those presented here; however, the examples discussed offer the reader an appreciation for the range of severity and complexity that may be found in affected horses. The veterinarian is obligated to provide the best possible care for the patient and to relieve animal suffering. The lack of definitive evidence for heritability of many of these defects can place the veterinarian in an untenable position, particularly when presented with literature that proclaims or suggests without evidence that a particular condition is inherited. I...
Bernoco D, Bailey E.Severe combined immunodeficiency disease (SCID) of horses is an autosomal, recessive hereditary disease occurring among Arabian horses. The genetic defect responsible for this disease was recently identified as a 5-basepair deletion in the gene encoding DNA-protein kinase catalytic subunit (DNA-PKcs). Horses with one copy of the gene appear normal, while horses with two copies of the gene manifest the disease. The present report describes a PCR-based test for detection of the gene defect and the results from testing 250 randomly selected Arabian horses. The frequency of SCID gene carriers was ...
The Journal of heredityMarch 6, 1998
Volume 89, Issue 1 104-106 doi: 10.1093/jhered/89.1.104
Duffield DA, Goldie PL.In a study of 2,786 tobiano and non-tobiano horses involved in paint horse breeding programs throughout the United States, the inheritance of the tobiano color pattern gene was tracked in pedigrees using the tightly linked polymorphic albumin gene. The dominant tobiano allele (T(o)), which produces the tobiano spotting pattern in horses, was in coupling with both AIA and AIB alleles at the albumin locus. The frequency of the T(o):AIA linkage phase among all the homozygous tobiano horses in this study including offspring and parents (N = 127), was 0.08. The T(o):AIB linkage phase was the most f...
Ekman S, Carlson CS.Osteochondrosis is a disorder of epiphyseal cartilage about which there is considerable confusion in the literature. We believe that this is due to the fact that osteochondrosis has been studied in the chronic stage when the lesions are morphologically complicated and the initial causative insult is impossible to determine. The etiology of osteochondrosis appears to be multifactorial, with trauma, hereditary factors and rapid growth, nutritional factors, and ischemia all having a role in its pathogenesis. Although predilection sites are variable among species, the morphology of the early lesio...
Woolf CM.Arabian bay horses manifest, on the average, more common white markings in their hind legs than their forelegs (anteroposterior asymmetry) and more common white markings in their left legs than their right legs (directional asymmetry). To determine if genetic variation exists for these types of asymmetry, the phenotypic response was studied in bay foals when their dams and sires were selected for the directions of fore-hind and left-right differences. In the fore-hind studies, the quantitative shifts in the bay foals were in the direction specified by the selection scheme and the observed devi...
Dolvik NI, Gaustad G.The degree of lameness of 265 randomly selected three-year-old standardbred trotters was assessed on a fixed point scale with 0 indicating soundness and 5 indicating that the animals were not weightbearing. Two variables were used to describe the signs of lameness; one was the continuous variable: the sum of the initial lameness score and the lameness scores after separate flexion tests of the carpal, stifle/tarsal and phalangeal joints and the second was the bivariate variable; the ratio of lame/sound horses. The mean (sd) heritability of the continuous variable was estimated to be 0.25 (0.21...
Weinhart G, Götz E, Götz HJ.Polydactylism, an excess deformity in a foal is described. The hereditary pathology and etiopathogenesis are discussed. A method of surgical correction of the deformed extremity is introduced. Indication and prognosis of the surgical correction of polydactylism and aspects concerning the breeding management are discussed.
Dik KJ, van den Broek J.From progeny lists of 30 Dutch Warmblood sires, 586 3-year-old females by these stallions were randomly selected, each progeny group aimed at 20 animals for statistical reasons. The front feet of the sires and female progeny were examined radiographically using lateromedial and dorsopalmar upright pedal projections. The radiological features associated with navicular disease were classified 0-4 using a standardised classification, grades 3 and 4 representing the more severe changes. The shape of the proximal articular border of the navicular bone outline on the dorsopalmar view was classified ...
Kakoi H, Gawahara H, Miura N.An unusual D system phenogroup appeared in one family line of Anglo-Arab horse. This phenogroup probably originated from inheritance with an apparent absence of factors and was transmitted through successive generations.
The Journal of heredityMay 1, 1994
Volume 85, Issue 3 222-224 doi: 10.1093/oxfordjournals.jhered.a111439
Bowling AT.Analysis of selected studbook records of the American Paint Horse Association, consisting of 687 foals sired by 13 overo stallions from non-overo mares, supports the inheritance of overo spotting as an autosomal dominant gene. More than one gene may control patterns registered as overo. Additional studies are necessary to explain the sporadic occurrence of overo spotting from nonspotted quarter horse parents and to confirm the inheritance of overo spotting in other breeds.
Parlevliet JM, Kemp B, Colenbrander B.The semen characteristics and testicular size of 398 3-year-old maiden Dutch Warmblood stallions were studied during February and March. Mean values (+/- SD) of age (1030 +/- 88 days) and testicular size (9.8 +/- 0.9 cm) of the maiden stallions were determined as well as the following semen characteristics (mean of two ejaculates, taken 1 h apart): volume (65 +/- 26 ml), sperm concentration (2.061 +/- 1.685 x 10(8) ml-1), total number of spermatozoa (1.129 +/- 0.71 x 10(10)), percentage of progressively motile spermatozoa (68 +/- 9%), percentage of live spermatozoa with normal morphology (66 +...
Grøndahl AM, Dolvik NI.Radiography of the tibiotarsal and metacarpo- and metatarsophalangeal joints was performed on 753 Standardbred trotters (6 to 21 months old) born in 1988. The surveyed population was drawn at random from all parts of Norway and represented about 60% of Standardbred trotters born the same year. Osteochondrosis in the tibiotarsal joint was diagnosed in 108 (14.3%) horses, and the prevalence of disease in progeny groups > 10 ranged from 0 to 69%. Bony fragments in the palmar/plantar portion of the metacarpo- and metatarsophalangeal joints were diagnosed in 89 (11.8%) horses, and the prevalence of...
Mitton JB, Schuster WS, Cothran EG, De Fries JC.Specific formulations are derived for the correlation between the heterozygosity of a randomly mating parent and its offspring for a diallelic locus, and for the correlation when multiple loci are considered. The expected correlation is maximal, approaching r = 0.50, when allelic frequencies are highly asymmetric, and it is zero when the allelic frequencies are equal to 0.50. Parent-offspring correlations, up to a maximum of 0.50 for diallelic loci, indicate that levels of heterozygosity can respond to selection. Multilocus allozyme data from limber pine, Pinus flexilis, and from horses of sta...
Gaughan EM, DeBowes RM.Many questions concerning heritability arise when a veterinarian is asked to supervise and treat disease of congenital origin. Genetic counseling, ethics, and legality are often confronted in discussions between animal health professionals and laymen in animal industry. Guidelines have been offered as in the 1984 statement of the Judicial Council of the American Veterinary Medical Association: "Performance of surgical procedures in all species for the purpose of concealing genetic defects in animals to be shown, raced, bred, or sold as breeding animals is unethical. However, should the health ...
Ohnesorge B, Deegen E, Miesner K, Geldermann H.Laryngoscopic examination during sedation was performed on 24 stallions and on their offspring (240 foals and 474 adult horses). Additionally the dams (n = 308) of 35 foals and 216 horses were examined. With the bilateral comparison of the arytaenoid movements the function of the abductory and adductory laryngeal muscles were evaluated and the left abductory dysfunction (idiopathic laryngeal hemiplegia, ILH) was divided into six degrees. The incidence and degree of ILH depended on age and the occurrence of the same dysfunction in the parents. Foals suffered in significantly lower number (24.7 ...
Ojala M, Ala-Huikku J.From 1974 to 1979, seven stillborn foals with internal hydrocephalus were encountered from one Standardbred trotter stallion which sired 239 registered foals. An hydrocephalic foal was also aborted by a daughter of the same stallion. One affected foal from Standardbred trotters and one from a Finnish Horses were also reported. In some cases, the condition caused severe dystocia. Based on field data, possible causes of the defect could neither be proved nor specifically overruled in individual cases. Hydrocephalus was obviously not an autosomal recessive single-locus defect, nor was it X-linked...
Marti E, Gerber H, Lazary S.The horses studied were of the Swiss Warmblood breed and most were ELA-typed to assess a possible association of dermal hypersensitivity to insect bites with the major histocompatibility complex. Firstly, the occurrence of the condition was examined in 304 half-siblings sired by six stallions (A to F). Fourteen cases of dermal hypersensitivity were recognized and all were in the 153 offspring of Stallions C, E and F. Most animals of this group were also investigated for chronic hypersensitivity bronchitis: none of the sires displayed clinical signs of dermal hypersensitivity, but Stallions D, ...
Jeffcott LB.This paper reviews current developments in equine osteochondrosis complex and the clinical syndromes associated with it. Although the primary lesion has been defined as a failure of endochondral ossification, its definitive cause is unknown and appears to involve heredity, growth rate, nutrition, mineral imbalance, endocrinological dysfunction and biomechanical trauma. Despite the international importance of osteochondrosis in horses, surprisingly few controlled investigations have been performed on its pathogenesis. The studies that have been conducted suggest that local effects on differenti...
Willham RL, Wilson DE.Research on the racing performance of quarter horses has been used to develop genetic prediction summaries on all horses with at least one start on record at the American Quarter Horse Association. In the 1987 summary, records from a total of 212,065 horses were used to give genetic predictions on stallions, mares, geldings, fillies, and colts. A reduced animal model was used that incorporated the repeated records of individuals. The individual race was the contemporary group after the data were adjusted for distance, sex, and age. Estimates of heritability of .24 and repeatability of .32 sugg...
The Journal of heredityMarch 1, 1991
Volume 82, Issue 2 167-169 doi: 10.1093/oxfordjournals.jhered.a111053
Woolf CM.Common white facial and leg markings have a multifactorial mode of inheritance in Equus caballus. Evidence for the complexity of the genetic component is the observation that chestnut (e/e) horses have more extensive white markings than do bay (E/-) horses. Computerized records obtained from the Arabian Horse Registry of America, Inc., were used to determine if heterozygous (E/e) bay horses have more extensive white facial markings than do homozygous (E/E) bay horses. Thirty-five sire families were analyzed. Each sire family consists of a sire, his foals, and the dams of those foals. The facia...
Cothran EG, Henney PJ, King JA.The inheritance of the equine Tf F3 allele was examined in 39 parent-offspring combinations. For 26 of the cases the allele inherited by the offspring from the heterozygous parent could be determined. The proportion of individuals that inherited the F3 variant compared to the alternative allele was exactly 1:1. In five cases the parental phenotype was identical to that of the offspring. For the remaining eight cases the parent was homozygous for the F3 allele and all offspring had the F3 allele. The results were consistent with Mendelian inheritance.
The Journal of heredityJuly 1, 1990
Volume 81, Issue 4 323-331 doi: 10.1093/oxfordjournals.jhered.a110997
Sponenberg DP, Carr G, Simak E, Schwink K.The leopard complex of white spotting patterns in horses consists of the leopard, few-spot leopard, blanket, blanket with spots, varnish roan (or marble), snowflake, frosted, speckled, and mottled patterns. Horses with any of these patterns can produce the other patterns when mated to nonpatterned horses. Twenty-two horses of the Welsh Pony, Noriker, Appaloosa, and Pony of the Americas breeds produced 270 foals in a distribution consistent with a single dominant allele being responsible for the patterns. The symbol for this dominant allele, Lp, is retained from previous work on the leopard pat...
The Journal of heredityJuly 1, 1990
Volume 81, Issue 4 250-256 doi: 10.1093/oxfordjournals.jhered.a110987
Woolf CM.The results of a previous study were compatible with the hypothesis that common white facial markings in the Arabian horse have a multifactorial mode of inheritance. I expanded that study to (1) include the legs and therefore obtain insight into the heritability of common white markings in all peripheral regions (face and legs) of the Arabian horse and (2) investigate the influence of sex and the genotypes that produce the bay and chestnut phenotypes on the variation in common white markings. Both studies were based on computerized data obtained from the Arabian Horse Registry of America, Inc....
Merkt H, Klug E.The rules for the minimal requirements in health and genital potency for stallions formulated by GOTZE (1950) are reformulated, taking into consideration the results achieved by KLUG (1982) and KENNEY (1983). A stallion must be free of phenotypic hereditary faults. Furthermore he has to be in general and genital health and must be fit in both, potentia coeundi and generandi. The figures are based on the examination of thoroughbred and so called "warmblood" stallions. However, they can be adapted to other breeds like draughthorses and ponys.
Li JK, Moloney BK, Shupe JL, Gardner EJ, Leone NC, Elsner Y.Genomic DNA polymorphisms obtained by restriction fragment-length polymorphism from healthy horses and horses with hereditary multiple exostoses were analyzed. These DNA were digested by 12 restriction enzymes and were hybridized against 6 isotopically labeled oncogene probes. Hybridization was not detected with the viral oncogene, v-ras, which indicated this oncogene was absent in the equine genome. Oncogenes (c-raf-1, c-fes, c-myb, c-myc, and c-sis) were present and had similar hybridization patterns and signal intensities in DNA from healthy horses and horses with hereditary multiple exosto...
The Journal of heredityMay 1, 1989
Volume 80, Issue 3 173-178 doi: 10.1093/oxfordjournals.jhered.a110831
Woolf CM.The hypothesis was tested that white facial markings in the Arabian horse show multifactorial inheritance. The hypothesis assumes that (1) alleles at different loci acting in a cumulative manner influence the variation in white facial markings, (2) the amount of whiteness is correlated with the number of genes, and (3) interacting nongenetic factors influence the variation. The study was based on computerized data obtained from the Arabian Horse Registry of America, Inc. The facial region was divided into five areas, and each horse was given a score according to the number of areas with a whit...
Rozhkov IuI, Okhapkin SK, Vorob'ev EG, Bezenko SP, Galimov IR.A stabilizing selection which is made in cattle according to phenotypic characters affects simultaneously a genetic character--the level of individual heterozygosity++. As a result animals with mean (modal) level of heterozygosity++ have the least probability of elimination. Similarly, the driving selection in pigs and horses leads to a change in both phenotypic characters and genetic character, the level of individual heterozygosity++. In this case the most heterozygous animals have the least probability of elimination.
Broström H, Fahlbrink E, Dubath ML, Lazary S.The distribution of equine leucocyte antigens (ELA) in Swedish Halfbreds affected by sarcoid tumors was determined and compared with that of control horses of the same breed. ELA-haplotype A3W13 appeared more frequently in affected horses, resulting in a chi 2 value of 4.45 (P = 0.034) for A3 and 9.05 (P = 0.0026) for W13, respectively. The relative risk factor (RR) could be estimated to 2.13 and 3.00 for A3 and W13, respectively. The etiology fraction (EF) was calculated to 28% and 37% for A3 and W13, respectively. Thus, in the population of Swedish Halfbreds approximately 40% (at least) of t...
Gaffney B, Cunningham EP.Thoroughbred horses have been bred exclusively for racing in England since Tudor times and thoroughbred horse racing is now practised in over 40 countries and involves more than half-a-million horses worldwide. The genetic origins of the thoroughbred go back largely to horses imported from the Middle East and North Africa to England in the late seventeenth and early eighteenth centuries. Since the establishment of the Stud Book in 1791, the population has been effectively closed to outside sources, and over 80% of the thoroughbred population's gene pool derives from 31 known ancestors from thi...
Stock KF, Hoeschele I, Distl O.Simulated horse data were used to compare multivariate estimation of genetic parameters and prediction of breeding values (BV) for categorical, continuous and molecular genetic data using linear animal models via residual maximum likelihood (REML) and best linear unbiased prediction (BLUP) and mixed linear-threshold animal models via Gibbs sampling (GS). Simulation included additive genetic values, residuals and fixed effects for one continuous trait, liabilities of four binary traits, and quantitative trait locus (QTL) effects and genetic markers with different recombination rates and polymor...
van Weeren PR, Denoix JM.Juvenile osteochondral conditions (JOCC) have a major impact on the equine industry and include many musculoskeletal disorders of the young horse, of which osteochondrosis (OC) is the most prominent. The Breeding, Osteochondral Status and Athletic Career (BOSAC) project is the first large, comprehensive, longitudinal field study on the subject conducted in three breeds of performance horses (Thoroughbreds, Standardbred Trotters and Warmbloods) that were monitored in their natural environment where they were reared under common field conditions. The BOSAC study used a radiographic protocol desi...
Polak G, Gurgul A, Jasielczuk I, Szmatoła T, Krupiński J, Bugno-Poniewierska M.Traditionally, pedigree-based relationship coefficients were used to manage inbreeding and control inbreeding depression that occurs within populations. The extensive incorporation of genomic data in livestock breeding creates the opportunity to develop and implement methods to manage populations at the genomic level. Consequently, the realized proportion of the genome that two individuals share can be more accurately estimated instead of using pedigree information to estimate the expected proportion of shared alleles. To make use of this improvement, in this study we evaluated the genomic inb...
Rozhkov IuI, Okhapkin SK, Vorob'ev EG, Bezenko SP, Galimov IR.A stabilizing selection which is made in cattle according to phenotypic characters affects simultaneously a genetic character--the level of individual heterozygosity++. As a result animals with mean (modal) level of heterozygosity++ have the least probability of elimination. Similarly, the driving selection in pigs and horses leads to a change in both phenotypic characters and genetic character, the level of individual heterozygosity++. In this case the most heterozygous animals have the least probability of elimination.
Diesterbeck U, Distl O.Navicular disease or podotrochlosis has long been known to cause forelimb lameness in horses. It had been proposed that the development of podotrochlosis has similarities to the human osteoarthritis (OA) complex. Alterations of the navicular bone can be made visible early in life only on the basis of radiographs. Reports on the prevalences of navicular disease indicate that radiological alterations in the navicular bone are present in different warmblood populations at frequencies of between 14.9% and 87.6%. Genetic factors play an important role in the development of the radiological signs. E...
Lassaline-Utter M, Gemensky-Metzler AJ, Scherrer NM, Stoppini R, Latimer CA, MacLaren NE, Myrna KE.To describe the clinical presentation, treatment, and outcome of a corneal dystrophy in Friesian horses and to analyze affected horses' pedigrees to investigate its heritability. Methods: Nine Friesians with bilateral disease were identified. Methods: Retrospective medical record review was used to identify Friesian horses exhibiting bilateral symmetric corneal lesions. Variables identified from medical records included patient sex and age at diagnosis; location, depth and size of corneal lesions; medical and surgical therapy instituted; and visual outcome. A four-generation pedigree for each ...
Silva AP, Curi RA, Langlois B, Silva JA.In this study, we estimated the heritability (h(2)) of earnings in the Quarter Horse in order to evaluate the inclusion of this trait in breeding programs. Records from 14,754 races of 2443 horses from 1978-2009 were provided by Sorocaba Hippodrome, São Paulo, Brazil. All ancestors of the registered horses were included in the pedigree file until the 4th generation. Log-transformed performance measures (LPM) were analyzed for animals aged 2, 3, and 4 years and during their entire career. The h(2) estimates were obtained using a multi-trait model and Gibbs sampling that included the effects of...
Stock KF, Distl O.To determine whether selection schemes accounting for orthopedic health traits were compatible with breeding progress in performance parameters in Hanoverian Warmblood horses. Methods: 5,928 horses. Methods: Relative breeding values (RBVs) were predicted for osseous fragments in fetlock (metacarpo- and metatarsophalangeal) and tarsal joints, deforming arthropathy in tarsal joints, and pathologic changes in distal sesamoid bones. Selection schemes were developed on the basis of total indices for radiographic findings (TIR), dressage (TID), and jumping (TIJ). Response to selection was traced ove...
Gaffney B, Cunningham EP.Thoroughbred horses have been bred exclusively for racing in England since Tudor times and thoroughbred horse racing is now practised in over 40 countries and involves more than half-a-million horses worldwide. The genetic origins of the thoroughbred go back largely to horses imported from the Middle East and North Africa to England in the late seventeenth and early eighteenth centuries. Since the establishment of the Stud Book in 1791, the population has been effectively closed to outside sources, and over 80% of the thoroughbred population's gene pool derives from 31 known ancestors from thi...
de Oliveira Bussiman F, Carvalho RSB, E Silva FF, Ventura RV, Ferraz JBS, Mattos EC, Eler JP, Balieiro JCC.Multitrait models can increase the accuracy of breeding value prediction and reduce bias due to selection by using traits measured before and after it has occurred. However, as the number of traits grows, a similar trend is expected for the number of parameters to be estimated, which directly affects the computing power and the amount of data required. The aim of the present study was to apply reduced rank (principal components model-PCM) and factor analytical models (FAM), to estimate (co)variance components for nineteen traits, jointly evaluated in a single analysis in Campolina horses. A to...
Perdomo-González DI, García de Paredes RLA, Valera M, Bartolomé E, Gómez MD.The studbook of Pura Raza Menorquina horses only permits the use of black-coated animals with a small quantity of white marks as breeding stock. Its breeding program uses linear morpho-functional traits as selection criteria. Our aim was to estimate the genetic parameters of linear morpho-functional traits, and reveal relationship of quality of black coat color (QB) and percentage of white marks (WM) with the other morphological and functional linear traits in this breed. A total of 46 linear traits were scored by four appraisers using seven classes, with a total of 772 records from 333 animal...
Gerber V, Tessier C, Marti E.Genetic predispositions for guttural pouch tympany, recurrent laryngeal neuropathy and recurrent airway obstruction (RAO) are well documented. There is also evidence that exercise-induced pulmonary haemorrhage and infectious diseases of the respiratory tract in horses have a genetic component. The clinical expression of equine respiratory diseases with a genetic basis results from complex interactions between the environment and the genetic make-up of each individual horse. The genetic effects are likely to be due to variations in several genes, i.e. they are polygenic. It is therefore unlikel...
Górecka A, Słoniewski K, Golonka M, Jaworski Z, Jezierski T.There are studies on the relationship between the position and shape of hair whorls on bovine forehead and phenotypic traits. According to anecdotal beliefs by horse users and handlers, temperamental traits may be related to the position of hair whorls in horses. No previous research on the mechanisms of inheritance of hair whorls has been performed, so the aim of the present study was to determine the heritability of the position of the hair whorl on the forehead of Konik horses. The horses (n = 362) were classified into five groups based on the whorl position on forehead with respect to the ...
Dusek J, Munk Z.The breeding documentation of the English Thoroughbred horse breeding farm at Napajedla was analyzed to study some effects acting upon the fertility of studs and mares and the length of gravidity. The heritability of fertility is the subject of this report. The normality of the distribution of fertility was tested by processing 300 data on fertility at the given significance level sup / Fn(xi) - F(xi) / less than or equal to Dn(a). The value of the supreme D(300) = 0.108 is lower than the critical level for alpha 0.05. The estimation of fertility heritability coefficient indicates that h2 = 0....
Ablondi M, Summer A, Vasini M, Simoni M, Sabbioni A.Horses are nowadays mainly used for sport and leisure purposes, and several local breeds, traditionally used in agriculture, are exposed to the risk of extinction. The long-term survival of local horse breeds depends on strategies to both monitor their genetic diversity and to find their sustainable role in the equine market. Thus, several local horse breeds need to adapt their breeding objective to allow a modernization process. The Bardigiano is an example of such horse breeds; we, therefore, studied the existing evaluation protocol from a genetic standpoint to assess the protocol's suitabil...
Väihkönen LK, Ojala M, Pösö AR.In red blood cell membranes, the activity of the main lactate carrier, H+-monocarboxylate co-transporter (MCT), varies interindividually and its distribution is bimodal. To show the repeatability of MCT activity, 2 to 5 blood samples were taken, at an interval of approximately 1 year, from 51 Standardbred horses, age 2 weeks-8 years, for a total of 128 observations. The horses could be divided into low (LT) and high (HT) lactate transport activity groups. Age significantly affected (P<0.05) MCT activity such that activity was highest in foals, reached a nadir at 2-3 years, and tended to inc...
Dierks C, Löhring K, Lampe V, Wittwer C, Drögemüller C, Distl O.A genome-wide scan was performed to detect quantitative trait loci (QTLs) for osteochondrosis (OC) and osteochondrosis dissecans (OCD) in horses. The marker set comprised 260 microsatellites. We collected data from 211 Hanoverian warmblood horses consisting of 14 paternal half-sib families. Traits used were OC (fetlock and/or hock joints affected), OCD (fetlock and/or hock joints affected), fetlock OC, fetlock OCD, hock OC, and hock OCD. The first genome scan included 172 microsatellite markers. In a second step 88 additional markers were chosen to refine putative QTLs found in the first scan....
Masuda M, Nikadori A, Nikadori E, Uchida N, Takizawa Y, Ishimaru M, Yamamoto T, Yuasa R, Kugai H, Nagahama Y, Takasu M, Tozaki T.The Miyako horse is a native Japanese horse breed. As with other native Japanese horses, the number of Miyako horses decreased due to mechanization and motorization, which reduced their roles, with just 14 in 1980. Although their population had increased to 55 horses by 2021, a further increase in their numbers is required to avoid extinction. Recently, their breeding has involved natural mating during group grazing; therefore, pedigree management has been difficult, and individual identification has been inconclusive. With the aim of formulating an effective breeding plan, this study used mic...
Physick-Sheard P, Kraus M, Basrur P, McGurrin K, Kenney D, Schenkel F.To assess evidence for genetic contributions to atrial fibrillation (AF) in the Standardbred horse. Methods: Equine referrals to the Ontario Veterinary College Health Sciences Centre (OVCHSC) for 1985-2009, and age and gait matched breed registry controls. Methods: Breeds presenting ≥ 5 times annually were tabulated (admission year and diagnosis; total 40,039; AF 396; no AF 39,643), and breed and year effects examined. Heritability and inbreeding coefficients were determined for Standardbred AF cases and racing contemporaries, and odds ratios for AF were calculated for frequently occurring s...
Eriksson S, Grandinson K, Fikse WF, Lindberg L, Mikko S, Broström H, Frey R, Sundquist M, Lindgren G.There is a lack of knowledge about the genetic background of eczema due to insect bite hypersensitivity, also called summer eczema, in horses. The condition is known in several horse breeds and countries and it causes reduced welfare of the horse and economic losses to the owner. The aim of this study was to estimate genetic parameters for summer eczema in Swedish-born Icelandic horses. A questionnaire was sent to owners of horses sired by stallions with more than 50 offspring born in Sweden between 1991 and 2001. Variance components of summer eczema classified as healthy, mild, moderate or se...
Todd ET, Hamilton NA, Velie BD, Thomson PC.Horses produce only one foal from an eleven-month gestation period, making the maintenance of high reproductive rates essential. Genetic bottlenecks and inbreeding can increase the frequency of deleterious variants, resulting in reduced reproductive levels in a population. In this study we examined the influence of inbreeding levels on foaling rate, gestation length and secondary sex ratio in Australian Thoroughbred mares. We also investigated the genetic change in these traits throughout the history of the breed. Phenotypic data were obtained from 27,262 breeding records of Thoroughbred mares...
Urschel KL, McKenzie EC.Skeletal muscle comprises 40% to 55% of mature body weight in horses, and its mass is determined largely by rates of muscle protein synthesis. In order to support exercise, appropriate energy sources are essential: glucose can support both anaerobic and aerobic exercise, whereas fat can only be metabolized aerobically. Following exercise, ingestion of nonfiber carbohydrates and protein can aid muscle growth and recovery. Muscle glycogen replenishment is slow in horses, regardless of dietary interventions. Several heritable muscle disorders, including type 1 and 2 polysaccharide storage myopath...
Ricard A, Perrocheau M, Couroucé-Malblanc A, Valette JP, Tourtoulou G, Dufosset JM, Robert C, Chaffaux S, Denoix JM, Guérin G.Juvenile osteochondral conditions (JOCC) have been defined as lesions resulting from biomechanical influences (compressive, tensional or shear forces) on the developing and growing musculoskeletal system. They include different types of osteochondrosis, osteochondral fragmentation of the articular surface or of the periarticular margins, juvenile subchondral bone cysts, osteochondral collapse, avulsion fractures of epiphyseal (or metaphyseal) ossifying bone and 'physitis'. The aim of this study was to estimate heritability of JOCC in a sample of 2106 French Trotters from four different sources...
Ewart SL, Ramsey DT, Xu J, Meyers D.Anterior segment dysgenesis syndrome occurs frequently in Rocky Mountain horses and has two distinct ocular phenotypes: (1) large cysts originating from the temporal ciliary body or peripheral retina and (2) multiple anterior segment anomalies including ciliary cysts, iris hypoplasia, iridocorneal adhesions and opacification, nuclear cataract, and megalocornea. To determine if anterior segment dysgenesis syndrome is heritable in horses we performed ophthalmic examinations and collected pedigree information on horses (n = 516) in an extended Rocky Mountain horse pedigree. Logistic regressive se...
Schrurs C, Blott S, Dubois G, Van Erck-Westergren E, Gardner DS.Racehorses competing in short (i.e., ‘sprinters’), middle- or longer-distance (i.e., ‘stayers’) flat races are assumed to have natural variation in locomotion; sprinters having an innately shorter stride than stayers. No study has objectively tested this theory. Here, racehorses (n = 421) were categorised as sprinters, milers or stayers based on known race distance (n = 3269 races). Stride parameters (peak length and frequency) of those racehorses were collected from prior race-pace training sessions on turf (n = 2689; ‘jumpout’, n = 1013), using a locomotion monitoring device. Ped...
Fritz KL, McCue ME, Valberg SJ, Rendahl AK, Mickelson JR.Recurrent exertional rhabdomyolysis is a heritable disorder that results in painful skeletal muscle cramping with exercise in up to 10% of all Thoroughbred racehorses. Here, we report a genome-wide association study with 48 282 SNPs analyzed among 48 case and 37 control Thoroughbreds. The most significant SNPs spanned approximately 13 Mb on ECA16, and the P-value of the most significant SNP after correcting for population structure was 8.0 × 10(-6) . This region on ECA16 was further evaluated by genotyping 247 SNPs in both the initial population and a second population of 34 case and 98 contr...
Luttman AM, Komine M, Thaiwong T, Carpenter T, Ewart SL, Kiupel M, Langohr IM, Venta PJ.Tetranucleotide and pentanucleotide short tandem repeat (hereafter termed tetraSTR and pentaSTR) polymorphisms have properties that make them desirable for DNA profiling and paternity testing. However, certain species, such as the horse, have far fewer tetraSTRs than other species and for this reason dinucleotide STRs (diSTRs) have become the standard for DNA profiling in horses, despite being less desirable for technical reasons. During our testing of a series of candidate genes as potentially underlying a heritable condition characterized by megaesophagus in the Friesian horse breed, we foun...
May-Davis S, Doveren A, Sweere R, Smak J, Vermeulen Z.Hereditary multiple exostoses (HME) is a condition rarely diagnosed in horses, which has not been previously reported in Dutch Warmblood horses. Its presentation resembles that diagnosed in humans, and it is predominantly active during periods of skeletal maturation. This case study reports a link between a granddam with no obvious HME lesions and its first and second generations presenting with HME, albeit with different sires. The severity in affected horses (n = 5) varied from one foreleg to the other with extensive multiple lesions of 123 of 205 bones in a half sibling in the first genera...
Stewart ID, White IM, Gilmour AR, Thompson R, Woolliams JA, Brotherstone S.Eventing competitions in Great Britain (GB) comprise three disciplines, each split into four grades, yielding 12 discipline-grade traits. As there is a demand for tools to estimate (co)variance matrices with a large number of traits, the aim of this work was to investigate different methods to produce large (co)variance matrices using GB eventing data. Data from 1999 to 2008 were used and penalty points were converted to normal scores. A sire model was utilised to estimate fixed effects of gender, age and class, and random effects of sire, horse and rider. Three methods were used to estimate (...
Posta J, Komlósi I, Mihók S.The aims of this study were to estimate phenotypic and genetic parameters for a range of traits in Hungarian Sport Horses, and to compare several methods of estimating breeding value (BV) in this breed. The analyses were based on the Hungarian Sport Horse Studbook, results of self-performance tests (SPTs) and show-jumping competition results. An SPT comprises subjective judgement of conformation traits, movement analysis traits and free-jumping performance, assessed via ordinal scores. Genetic parameters of SPTs were estimated with an animal model. Different measurements of the competition per...
