Quarter Horses Research Articles

Equine herpesvirus-1 genotype did not significantly affect clinical signs and disease outcome in 65 horses diagnosed with equine herpesvirus-1 myeloencephalopathy

The objective of this study was to determine if the genotype of equine herpesvirus-1 (EHV-1) impacted clinical disease and outcome of horses with laboratory confirmed equine herpesvirus myeloencephalopathy (EHM). Medical records from 65 horses diagnosed with EHM from 2011 to 2019 were reviewed for signalment, presence and severity of clinical signs (lethargy, fever, ataxia, urinary incontinence) and outcome. Horses were further grouped based on the EHV-1 genotype into neuropathic (D752) or non-neuropathic (N752) EHV-1 infection. Between the two EHV-1 genotype groups, age and sex distributions were similar, although breed distribution was different (Quarter Horses and Saddlebreds were overrepresented and Warmbloods were underrepresented in the EHV-1 D752 group compared to the EHV-1 N752 group; P = 0.009). Lethargy, fever, ataxia and outcome were not significantly different between the two EHV-1 genotype groups (P > 0.05). However, urinary incontinence was significantly more frequently reported in horses infected with the D752 genotype of EHV-1 (P=0.04). Contrary to previous studies, the present study showed no difference in frequency of genotype (D752 or N752) among 65 horses with EHM and, with the exception of urinary incontinence, no difference in clinical disease or outcome related to the EHV-1 genotype.

Quantitative magnetic resonance imaging and histological hoof wall assessment of 3-year-old Quarter Horses.

Few noninvasive methods are available for equine hoof wall evaluation. The highly organised wall structures and composition of proteoglycans and collagens may make this region amenable to quantitative MRI (qMRI) techniques of T1ρ and T2 mapping to identify pathology related to proteoglycan content and collagen organisation respectively. To establish normative T1ρ and T2 values of the equine hoof wall of 3-year-old Quarter Horses with histological comparison. Cadaveric anatomical study. Six cadaveric left thoracic feet from 3-year-old racing Quarter Horses with no reported lameness were evaluated using T1ρ and T2 mapping. Mapping was performed at six regions of interest at the toe of each hoof including proximal and distal regions of the inner epidermis, stratum lamellatum and corium. Histology was evaluated for standard hoof morphology and proteoglycan staining. T2 values of the stratum lamellatum and corium were similar (42.9 [95% CI: 41.6-44.2]ms and 44 [95% CI: 42.7-45.3]ms respectively), but both were significantly different to the inner epidermis (35.8 [95% CI: 34.5-37.1]ms, P<0.001). T1ρ values for the inner epidermis, stratum lamellatum and corium were significantly different (25.1 [95% CI: 23.1-27.1]ms, 44.4 [95% CI: 42.4-46.4]ms and 50.1 [95% CI: 48.1-52.1]ms, respectively, P<0.001). Histology demonstrated normal organised morphology. Proteoglycan staining was only visible in the stratum lamellatum and corium. Cadaveric study with frozen samples used. Variation of qMRI metrics through the depth of the equine hoof wall was found. Although the highly ordered environment of collagen may contribute to T2 values, there was lack of evidence to support proteoglycan content as a major contributor of T1ρ values. It is possible T1ρ values had a greater dependence on total water content as the lowest values were seen in the epidermis. Additional research using qMRI is needed to determine mapping values in different disease states.

Impact of alpha-tocopherol deficiency and supplementation on sacrocaudalis and gluteal muscle fiber histopathology and morphology in horses.

BackgroundA subset of horses deficient in alpha‐tocopherol (α‐TP) develop muscle atrophy and vitamin E‐responsive myopathy (VEM) characterized by mitochondrial alterations in the sacrocaudalis dorsalis medialis muscle (SC).ObjectivesTo quantify muscle histopathologic abnormalities in subclinical α‐TP deficient horses before and after α‐TP supplementation and compare with retrospective (r)VEM cases.AnimalsProspective study; 16 healthy α‐TP‐deficient Quarter Horses. Retrospective study; 10 retrospective vitamin E‐responsive myopathy (rVEM) cases .MethodsBlood, SC, and gluteus medius (GM) biopsy specimens were obtained before (day 0) and 56 days after 5000 IU/450 kg horse/day PO water dispersible liquid α‐TP (n = 8) or control (n = 8). Muscle fiber morphology and mitochondrial alterations were compared in samples from days 0 and 56 and in rVEM cases.ResultsMitochondrial alterations more common than our reference range (<2.5% affected fibers) were present in 3/8 control and 4/8 treatment horses on day 0 in SC but not in GM (mean, 2.2; range, 0%‐10% of fibers). Supplementation with α‐TP for 56 days did not change the percentage of fibers with mitochondrial alterations or anguloid atrophy, or fiber size in GM or SC. Clinical rVEM horses had significantly more mitochondrial alterations (rVEM SC, 13% ± 7%; GM, 3% ± 2%) and anguloid atrophy compared to subclinical day 0 horses.Conclusions and Clinical ImportanceClinically normal α‐TP‐deficient horses can have mitochondrial alterations in the SC that are less severe than in atrophied VEM cases and do not resolve after 56 days of α‐TP supplementation. Preventing α‐TP deficiency may be of long‐term importance for mitochondrial viability.

Breed and stallion effects on frozen-thawed semen in warmblood, light and quarter horses

The objectives of the present study were to analyze systematic effects on semen quality traits from fresh and frozen-thawed semen collected in and outside season. A total of 4,681 reports on semen traits of 121 stallions representing Arabian, Thoroughbred, Quarter Horse and four warmblood breeds used for artificial insemination at the Lower Saxon National stud Celle were edited for analysis of gel-free volume, sperm concentration, total number of sperm and total number of motile sperm in fresh semen and in frozen-thawed semen progressive motility, DNA fragmentation index and non-viable sperm. Month, year, age, breed and stallions effects were analyzed with a linear mixed model procedure. Breed differences were significant for sperm concentration, total number of sperm, total motile sperm number and DNA fragmentation index. Hanoverian stallions showed significant higher least squares means for sperm concentration, total number of sperm and total motile sperm number in fresh semen, whereas Thoroughbred had significant higher least squares means for DNA fragmentation index. Stallions with an age of 2–6 years had significant lower least squares means in sperm concentration, total number of sperm and total motile sperm number and progressively motile sperm post-thawing than the other age groups. Month was significant for all semen traits but progressively motile sperm post-thawing. Month by age class interaction showed a significant influence. Inter-stallion variance accounted for 27–71% and the two-way stallion by month interaction for 2–7% of the total variance of semen quality traits. The largest proportion of inter-individual variance among stallions was obtained for the DNA fragmentation index.

Efeito da gama-orizanol e L-carnitina sob parâmetros corporais, de performance e laboratoriais em equinos quarto-de-milha praticantes de três tambores

Os animais da raça quarto de milha são conhecidos por serem usados em diversas práticas e atividades, devido à sua alta ve­locidade. A constante busca pela melhora no ganho de massa muscular e recuperação em equinos, principalmente atletas, im­pulsiona as pesquisas para suplementos sem efeitos colaterais. O objetivo deste trabalho foi avaliar parâmetros clínicos e laborato­riais em animais dessa raça, suplementados com gama-orizanol e L-carnitina antes e após a execução da prova de três tambores. Esses equinos puros de origem recebiam 200 mililitros (ml) do suplemento Energy Horse® como suplementação alimentar mis­turados à ração para os estabulados, e via oral para os animais de piquete. Executaram o percurso de uma prova de tambor em pista de tamanho oficial em 3 momentos do experimento: dia 0, dia 30 e dia 60 após o tratamento. Os animais foram clinicamente exa­minados antes e após os exercícios (coloração de mucosas ocular e oral; frequência cardíaca; frequência respiratória; e motilidade intestinal), além da pesagem e coleta de sangue para dosagem de colesterol total, proteína total, aspartato aminotransferase (AST), alanina aminotransferase (ALT), gama glutamil transpeptidase (GGT), fosfatase alcalina (FA), creatinoquinase (CK) e glicose.&#x0D; Os dados foram avaliados empregando-se o teste de análise de variância (ANOVA), seguido de comparações múltiplas pelo teste de Tukey, segundo o programa estatístico PRISM, (Graph Prism for Windows, version 6.01, GraphPad, EUA). O nível de significância adotado para todos os testes empregados foi de 5% (p &lt; 0,05). Nossos resultados demonstraram que houve uma diferença sig­nificativa no aumento de peso dos animais tratados, menor fre­quência cardíaca e respiratória, além de importante diminuição do tempo de execução de prova dos animais atletas tratados em relação aos do grupo controle, especialmente 60 dias após o uso do suplemento e naqueles condicionados em baia. Portanto, o uso desse suplemento teve um impacto positivo no desempe­nho desses animais atletas que receberam a suplementação, em comparação aos animais não tratados, sem ocasionar qualquer prejuízo à saúde dos mesmos. E, uma vez que houve uma forte correlação negativa (r = -0,89) entre o ganho de peso corporal e tempo de execução da prova, pode-se afirmar que esse aumento do peso dos animais dado pela suplementação alimentar Energy Horse®, especialmente nos animais estabulados, está diretamente relacionado ao melhor desempenho no tempo da prova de três tambores por equinos da raça quarto de milha.

B-mode ultrasonography and gray scale histogram for evaluation of the nuchal ligament in Quarter horse

ABSTRACT: The gray scale histogram (GSH) makes it possible to measure the amount and distribution of gray shade frequencies, providing quantitative information on both echogenicity and echotexture of tissues. There is a need to diminish the subjectivity of the ultrasound images of the nuchal ligament (NL). This work proposes to evaluate the NL by ultrasound B-mode GSH images in different ages of Quarter horses. It used 15 healthy Quarter horses, which were classified by age into three different groups: “baby” (1), “sobreano” (2) and “adult” (3). The animals were submitted to chemical restraint for the ultrasound examination. Subsequently, the GSH tool was used in each image for statistical analysis. There was a significant difference between Mean and Mode between groups. Group 1 differed significantly when compared to Group 2 and 3. Group 2 presented superior echogenicity to Group 1 and 3. The height of the NL did not vary considerably between groups. GSH indicated that the echogenicity of NL in Quarter horses varies with age.

Protocols for preparation of platelet rich plasma (PRP) in Quarter Horses

ABSTRACT: This study compared two protocols for preparation of platelet rich plasma (PRP) and evaluated the association between manual and automated methods for platelet count using a prospective study design. Eight clinically healthy Quarter Horses had venous blood samples collected at rest. After collection, blood samples were centrifuged twice, using two different protocols including a period of sample resting, either at the start or at the end of the protocol. Platelet counting at the start of the protocol, during, and after obtaining PRP was conducted manually or with an automated counter, followed by comparison of the two methods. In order to investigate platelet degranulation during the protocol, vascular endothelial growth factor (VEGF) was measured at each preparation stage. The protocol with sample resting before centrifugation yielded a more concentrated PRP, and the study verified that both manual and automated methods are comparable and can be used interchangeably for platelet counting. VEGF concentration did not differ significantly between protocols, or among protocol stages. The results indicate that choice of protocol for PRP preparation will affect the quantity of platelets in the final product, although platelet degranulation was not observed as evidenced by the stable VEGF concentrations measured. A larger yield of non-degranulated platelets in PRP is desirable since more α-granules will be present, therefore Protocol II is recommended. Both manual and automated counts reliably allow clinicians to obtain platelet counts and the choice of utilizing a manual or automated method is unlikely to interfere with evaluation of the final PRP product.

A 10-year study of arthroscopic surgery in racing Thoroughbreds and Quarter Horses with osteochondral fragmentation of the carpus.

Osteochondral fragmentation of the carpus is a common cause of lameness in racehorses. Prognosis following arthroscopic removal of the fragments was reported in 1987, but little is known of recent success rates. To identify associations between the severity and location of osteochondral fragments in the carpus, and to describe the racing performance of horses pre- and post-surgery in Thoroughbreds and Quarter Horses. To identify factors associated with a horse racing post-surgery. Retrospective study of clinical records (2006-2016). Surgical and racing records for racehorses undergoing arthroscopic surgery of the carpus were collated during the 10-year study period. Signalment, location of osteochondral fragmentation and grade of defect left after removal and debridement identified and racing performance pre- and post-surgery were described, stratified by breed. Logistic regression analysis was used to identify factors associated with unsuccessful return to racing. In total, 828 horses (n=416 Quarter Horses; n=412 Thoroughbreds) underwent 880 carpal arthroscopies after fragments were found on radiography. Sixty-five percent (n=289) and 27% (n=118) of the lesions were bilateral in Quarter Horses and Thoroughbreds respectively (P<0.001). In both breeds, the most commonly affected bone was the dorsodistal radial carpal bone (n=320/659; 48.6%). Overall, 82% (n=686; n=358 Quarter Horses, n=328 Thoroughbreds) of horses raced post-surgery, with 69.5% (n=476; n=228 Quarter Horses, n=248 Thoroughbreds) racing at the same or a higher level of competition. Factors associated with horses not returning to racing post-surgery were increasing horse age, female horses, and a lesion grade of 4, while racing pre-surgery was protective. This study does not include a control population for comparison. There were significant differences between the location and severity of lesions in Quarter Horses, when compared to Thoroughbreds. The majority of horses return to racing following surgery, although performance was influenced by lesion severity. The Summary is available in Portuguese - see Supporting information.

Determinants of Undesirable Behaviors in American Quarter Horses Housed in Box Stalls

The objective of this study was to investigate the management practices that affect undesirable behaviors in American Quarter Horses (AQH) confined to box stalls. A total of 105 adult AQH, comprising 29 females, 22 intact males, and 54 castrated males, housed in box stalls for at least 30 days, were included in the study. Behavioral activities were recorded through visual inspection at 5-min intervals over a 24-h period by two observers who took turns in shifts of 4 hours. Parameters related to animal characteristics, stall conditions, handling, training, nutrients supplied, and feeding behaviors were considered independent variables, and the time spent in undesirable behaviors was the dependent variable. Data were subjected to exploratory factor analysis and hierarchical cluster analysis. Four principal components were extracted. Two clusters were identified based on the time spent in undesirable behaviors: low-incidence group (25 ± 13 minutes) and high-incidence group (97 ± 52 minutes). Nutritional status (P = .1447), physiological status (P = .1372), and training routine (P = .1160) had no significant effects on the dependent variable; however, the effect of feeding behavior (P = .0444) was significant. A low dry matter intake/requirement ratio (P = .0470) and a high heart rate at rest (P = .0444) indicated that inadequate nutrient supply is a determinant of the time spent in undesirable behaviors in AQH. Aspects related to management practices such as horse nutrition, feeding behaviors, and training routine should be considered to reduce undesirable behaviors in AQH.

Rapid Communication: Differential skeletal muscle mitochondrial characteristics of weanling racing-bred horses.

Responses of equine skeletal muscle characteristics to growth and training have been shown to differ between breeds. These differential responses may arise in part because muscle fiber type and mitochondrial density differ between breeds, even in untrained racing-bred horses. However, it is not known when these breed-specific differences manifest. To test the hypothesis that weanling Standardbreds (SB) and Thoroughbreds (TB) would have higher mitochondrial measures than Quarter Horses (QH), gluteus medius samples were collected from SB (mean ± SD; 6.2 ± 1.0 mo; n = 10), TB (6.1 ± 0.5 mo; n = 12), and QH (7.4 ± 0.6 mo; n = 10). Citrate synthase (CS) and cytochrome c oxidase (CCO) activities were assessed as markers of mitochondrial density and function, respectively. Mitochondrial oxidative (P) and electron transport system (E) capacities were assessed by high-resolution respirometry (HRR). Data for CCO and HRR are expressed as integrated (per mg protein and per mg tissue wet weight, respectively) and intrinsic (per unit CS). Data were analyzed using PROC MIXED in SAS v 9.4 with breed as a fixed effect. Mitochondrial density (CS) was higher for SB and TB than QH (P ≤ 0.0007). Mitochondrial function (integrated and intrinsic CCO) was higher in TB and QH than SB (P ≤ 0.01). Integrated CCO was also higher in TB than QH (P < 0.0001). However, SB had higher integrated maximum P (PCI+II) and E (ECI+II) than QH (P ≤ 0.02) and greater integrated and intrinsic complex II-supported E (ECII) than both QH and TB (P ≤ 0.02), whereas TB exhibited higher integrated P with complex I substrates (PCI) than SB and QH (P ≤ 0.003) and higher integrated PCI+II and ECI+II than QH (P ≤ 0.02). In agreement, TB and QH had higher contribution of complex I (CI) to max E than SB (P ≤ 0.001), whereas SB had higher contribution of CII than QH and TB (P ≤ 0.002). Despite having higher mitochondrial density than QH and TB, SB showed lower CCO activity and differences in contribution of complexes to oxidative and electron transport system capacities. Breed differences in mitochondrial parameters are present early in life and should be considered when developing feeding, training, medication, and management practices.

Effect of fiber and starch in concentrate feed on gastric ulcers in horses

Nine Quarter Horses were used in a 3 × 3 Latin square with replication to determine the effect of various levels of dietary starch on glycogen replenishment in the light working horse. Horses were fed Coastal bermudagrass hay at 1% BW/d with remaining calories met by a high (HS), medium (MDS), or low starch (LS) concentrate. Horses were transitioned to 1 of 3 diets over 7 d for a 14-d treatment period where they were then worked to fatigue in a standardized exercise test. Total diets provided an average of 1,206.67, 844.61, and 263.13 g of starch/d in HS, MDS, and LS, respectively. Horses were lightly exercised for 30 min 3 d/wk. Skeletal muscle biopsies were taken from the biceps femoris at rest, immediately after the standardized exercise test, and 24 and 48 h after exercise. Venous blood samples were taken at rest, immediately after exercise, 10 min after recovery, and 24 h after exercise. There was a greater resting muscle glycogen concentration (P = 0.009) when comparing HS with MDS (10.25 vs. 8.28 μg/mg wet weight). There was a greater concentration of glycogen 24 h after exercise (P = 0.04) when comparing LS with HS (9.52 vs. 7.68 μg/mg wet weight). High starch used more glycogen than MDS or LS. A slight reduction in glycogen after exercise for MDS and LS indicated that fat or protein may have been used as substrate for exercise. Results indicated that feeding 1,206.67 g of starch/d did not yield an advantage in recovery time over a MDS or LS diet.

Sale prices of recreational American Quarter Horses as an economic indicator

Sale prices of recreational American Quarter Horses as an economic indicator

Explicit evidence for a missense mutation in exon 4 of SLC45A2 gene causing the pearl coat dilution in horses.

Four loci seem responsible for the dilution of the basic coat colours in horse: Dun (D), Silver Dapple (Z), Champagne (CH) and Cream (C). Apart from the current phenotypes ascribed to these loci, pearl has been described as yet another diluted coat colour in this species. To date, this coat colour seems to segregate only in the Iberian breeds Purebred Spanish horse and Lusitano and has also been described in breeds of Iberian origin, such as Quarter Horses and Paint Horse, where it is referred to as the 'Barlink Factor'. This phenotype segregates in an autosomal recessive manner and resembles some of the coat colours produced by the champagne CHCH and cream CCr alleles, sometimes being difficult to distinguish among them. The interaction between compound heterozygous for the pearl Cprl and cream CCr alleles makes SLC45A2 the most plausible candidate gene for the pearl phenotype in horses. Our results provide documented evidence for the missense variation in exon 4 [SLC45A2:c.985G>A; SLC45A2:p.(Ala329Thr)] as the causative mutation for the pearl coat colour. In addition, it is most likely involved as well in the cremello, perlino and smoky cream like phenotypes associated with the compound CCr and Cprl heterozygous genotypes (known as cream pearl in the Purebred Spanish horse breed). The characterization of the pearl mutation allows breeders to identify carriers of the Cprl allele and to select this specific coat colour according to personal preferences, market demands or studbook requirements as well as to verify segregation within particular pedigrees.

Evaluation of a Novel System for Linear Conformation, Gait, and Personality Trait Scoring and Automatic Ranking of Horses at Breed Shows: A Pilot Study in American Quarter Horses

The study compared results of the traditional horse judging system (T) using subjective grades with those of a novel system of linear scoring (LS) using an application (“Breed Show App”). The horse's quality in relation to the total breeding aim was evaluated based on weighting factors for 57 individual traits commonly regarded in T, thus allowing immediate ranking of the horses. Results were stated as total grade in percent for both systems. One thousand nine hundred nine American Quarter horses were judged at regular breed shows with either T (n = 883), LS (n = 1,026), or both systems (n = 17). In addition, suitable traits for personality evaluation using LS were selected (n = 559 horses). Mixed-model analysis (F-test throughout) and Pearson correlations were used to assess agreement between systems and to identify highly correlated personality traits. Mean total grade was slightly greater in T (83.3 ± 0.2%) than LS (81.7 ± 0.3, P < .0001). Overall grades showed a wider range with LS, thus likely better reflecting phenotypic variance and improving comparability between horses without affecting overall horse ranking (r = 0.95, P < .00001) and thresholds for licensing minimum standards. Most personality traits deviated from a normal distribution (Kolmogorov-Smirnov: P < .01), potentially indicating that genetic or phenotypic preselection took place in the participating horses. Foals that were perceived as more “bright” by the observers kept a larger distance from their dam (r = 0.4) and showed more exploration of the environment (r = 0.2, all P < .01). Especially with more complex traits, including personality traits, variation of results and thus possibilities for differentiating between horses seem to be increased in horse judging using LS.

Effect of Cobalt Chloride on Fermentation of Alfalfa and Smooth Bromegrass Hays by Horse Cecal Microorganisms

Effects of Co on fiber digestibility in horses are largely unknown. Our objective was to evaluate effects of Co chloride on in vitro gas production, VFA production, and dry matter (DM) disappearance (IVDMD) using cecal fluid from 4 cannulated Quarter Horses. Five grams DM of alfalfa or smooth bromegrass hay were provided as substrate with Co added at 0.0, 0.5, 5.0, 25.0, or 50.0 mg/kg substrate DM. Ten milliliters cecal fluid and 140 mL McDougall's buffer were incubated in duplicate, and pH, VFA concentrations, and IVDMD were measured after 48 hours. Gas production, used as an indicator of fermentative activity, was recorded every 15 minutes. Terminal pH was not affected by Co or forage type (P > .19). There was greater IVDMD in cultures containing alfalfa (29.2%) compared with smooth bromegrass hay (19.4%; P < .01). There was a forage × Co interaction (P < .05) in which gas production was greater in cultures containing alfalfa, and 5 mg Co/kg substrate DM led to greater gas production than 50 mg Co/kg substrate DM in cultures containing brome (P < .05). Gas production was affected by forage, Co, and time (P < .01). Production of individual and total VFA, as well as acetate:propionate (A:P) ratio were increased in cultures containing alfalfa (P < .05); however, there were no effects of Co on VFA concentrations (P > .05). While gas production was influenced by Co in cultures containing brome, no effects of Co were observed for pH, VFA, or IVDMD.

A retrospective cohort study of racing performance in Quarter Horses undergoing prosthetic laryngoplasty for treatment of recurrent laryngeal neuropathy.

OBJECTIVE To determine effects of prosthetic laryngoplasty on return to racing, performance index, and career longevity in racing Quarter Horses with recurrent laryngeal neuropathy (RLN) and to evaluate performance variables for horses with RLN undergoing prosthetic laryngoplasty, compared with a control horse population. DESIGN Multicenter, retrospective cohort study. ANIMALS 162 racing Quarter Horses with RLN treated with prosthetic laryngoplasty (case horses) and 324 racing Quarter Horse without RLN (control horses). PROCEDURES Medical and race records of case and control horses examined at 5 referral centers between January 2000 and December 2015 were reviewed retrospectively. Two control horses were matched with each case horse. Return to racing, earnings, number of racing starts, performance index, and career longevity were evaluated. RESULTS The odds of returning to racing did not differ significantly between case and control horses but decreased with increasing age. Neither racing starts nor career longevity were affected by prosthetic laryngoplasty or by RLN grade. In fact, horses undergoing laryngoplasty for treatment of RLN and horses with the lowest RLN grade before surgery had higher performance indices after the surgery, compared with indices for control horses. CONCLUSIONS AND CLINICAL RELEVANCE The faster speeds and shorter distances raced with Quarter Horses could alter how RLN impacts respiratory variables and performance in Quarter Horses, compared with other racehorse breeds. Further study is needed to understand the impacts of RLN and surgical treatments for RLN in racing Quarter Horses.

Coding sequences of sarcoplasmic reticulum calcium ATPase regulatory peptides and expression of calcium regulatory genes in recurrent exertional rhabdomyolysis.

BackgroundSarcolipin (SLN), myoregulin (MRLN), and dwarf open reading frame (DWORF) are transmembrane regulators of the sarcoplasmic reticulum calcium transporting ATPase (SERCA) that we hypothesized played a role in recurrent exertional rhabdomyolysis (RER).ObjectivesCompare coding sequences of SLN, MRLN, DWORF across species and between RER and control horses. Compare expression of muscle Ca2+ regulatory genes between RER and control horses.AnimalsTwenty Thoroughbreds (TB), 5 Standardbreds (STD), 6 Quarter Horses (QH) with RER and 39 breed‐matched controls.MethodsSanger sequencing of SERCA regulatory genes with comparison of amino acid (AA) sequences among control, RER horses, human, mouse, and rabbit reference genomes. In RER and control gluteal muscle, quantitative real‐time polymerase chain reaction of SERCA regulatory peptides, the calcium release channel (RYR1), and its accessory proteins calsequestrin (CASQ1), and calstabin (FKBP1A).ResultsThe SLN gene was the highest expressed horse SERCA regulatory gene with a uniquely truncated AA sequence (29 versus 31) versus other species. Coding sequences of SLN, MRLN, and DWORF were identical in RER and control horses. A sex‐by‐phenotype effect occurred with lower CASQ1 expression in RER males versus control males (P < .001) and RER females (P = .05) and higher FKBP1A (P = .01) expression in RER males versus control males.Conclusions and Clinical ImportanceThe SLN gene encodes a uniquely truncated peptide in the horse versus other species. Variants in the coding sequence of SLN, MLRN, or DWORF were not associated with RER. Males with RER have differential gene expression that could reflect adaptations to stabilize RYR1.

Exome sequencing in genomic regions related to racing performance of Quarter Horses.

Among horses selected for speed, the racing line of Quarter Horses is characterized by high performance in sprint races, with these animals being considered the fastest horses in the world. However, few studies have investigated in more detail the polymorphisms and genes that act on this trait. The objective of this study was to analyze exomes and UTRs in regions previously associated with this trait by GWAS in Quarter Horse racehorses with contrasting maximum speed index (SImax), prospecting causal gene polymorphisms that are related to or are in strong linkage disequilibrium with racing performance. Genotypic and phenotypic records from 360 animals of the racing line of Quarter Horses, previously genotyped with an SNP chip to obtain individual genomic estimated breeding values for performance, were used for the formation and sequencing of two groups of animals with contrasting racing performance (20 animals with superior SImax and 20 with inferior SImax). Two rapid runs were performed using two pools of libraries containing 20 and 19 samples randomly chosen among the 40 samples with contrasting SIs. A total of 1203 variants (1105 SNPs and 93 InDels) were identified in 33 regions of interest obtained previously by GWAS. Twenty-nine of the polymorphisms (24 SNPs and 5 InDels) were considered to be important based on three different and independent approaches: SIFT scores classified as deleterious (< 0.05), degree of impact on the consensus region of each polymorphism, and different allele frequencies identified by Fisher's exact test (p < 0.01) between the groups of horses with contrasting SImax. Thus, eight genes described as functional and positional candidates in previous studies (ABCG5, COL11A1, GEN1, SOCS3, MICAL1, SPTBN1, EPB41L3, and SHQ1) and nine new candidate genes (AKNA, ARMC2, FKBP15, LHX1, NOL10, TMEM192, ZFP37, FIG4, and HNRNPU), some of them with known function, were related to racing performance in Quarter Horses.

Prevalence of the E321G MYH1 variant for immune-mediated myositis and nonexertional rhabdomyolysis in performance subgroups of American Quarter Horses.

BackgroundImmune‐mediated myositis (IMM) in American Quarter Horses (QHs) causes acute muscle atrophy and lymphocytic infiltration of myofibers. Recently, an E321G mutation in a highly conserved region of the myosin heavy chain 1 (MYH1) gene was associated with susceptibility to IMM and nonexertional rhabdomyolysis.ObjectivesTo estimate prevalence of the E321G MYH1 variant in the QH breed and performance subgroups.AnimalsThree‐hundred seven elite performance QHs and 146 random registered QH controls.MethodsProspective genetic survey. Elite QHs from barrel racing, cutting, halter, racing, reining, Western Pleasure, and working cow disciplines and randomly selected registered QHs were genotyped for the E321G MYH1 variant and allele frequencies were calculated.ResultsThe E321G MYH1 variant allele frequency was 0.034 ± 0.011 in the general QH population (6.8% of individuals in the breed) and the highest among the reining (0.135 ± 0.040; 24.3% of reiners), working cow (0.085 ± 0.031), and halter (0.080 ± 0.027) performance subgroups. The E321G MYH1 variant was present in cutting (0.044 ± 0.022) and Western Pleasure (0.021 ± 0.015) QHs at lower frequency and was not observed in barrel racing or racing QHs.Conclusions and Clinical ImportanceKnowing that reining and working cow QHs have the highest prevalence of the E321G MYH1 variant and that the variant is more prevalent than the alleles for hereditary equine regional dermal asthenia and hyperkalemic periodic paralysis in the general QH population will guide the use of genetic testing for diagnostic and breeding purposes.

Prevalence, anatomical distribution and risk factors associated with equine gastric ulceration syndrome in American Quarter Horses

Prevalence, anatomical distribution and risk factors associated with equine gastric ulceration syndrome in American Quarter Horses