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Summary: Fractures are medical conditions that compromise the athletic potential of horses and/or the safety of jockeys. Therefore, the reduction of fracture risk is an important horse and human welfare issue. The present study used molecular genetic approaches to determine the effect of genetic risk for fracture at four candidate SNPs spanning the myostatin (MSTN) gene on horse chromosome 18. Among the 3706 Japanese Thoroughbred racehorses, 1089 (29.4%) had experienced fractures in their athletic life, indicating the common occurrence of this injury in Thoroughbreds. In the case/control association study, fractures of the carpus (carpal bones and distal radius) were statistically associated with g.65809482T/C (P = 1.17 x 10‐8), g.65868604G/T (P = 2.66 x 10‐9), and g.66493737C/T (P = 6.41 x 10‐8). In the retrospective cohort study using 1710 racehorses born in 2000, the relative risk (RR) was highest for male horses at g.65868604G/T, based on the dominant allele risk model (RR = 2.251, 95% confidence interval 1.407–3.604, P = 0.00041), and for female horses at g.65868604G/T, based on the recessive allele risk model (RR = 2.313, 95% confidence interval 1.380–3.877, P = 0.00163). Considering the association of these SNPs with racing performance traits such as speed, these genotypes may affect the occurrence of carpus fractures in Japanese Thoroughbred racehorses as a consequence of the non‐genetic influence of the genotype on the distance and/or intensity of racing and training. The genetic information presented here may contribute to the development of strategic training programs and racing plans for racehorses that improve their health and welfare. [ABSTRACT FROM AUTHOR]

Summary: Despite strong selection for athletic traits in Thoroughbred horses, there is marked variation in speed and aptitude for racing performance within the breed. Using global positioning system monitoring during exercise training, we measured speed variables and temporal changes in speed with age to derive phenotypes for GWAS. The aim of the study was to test the hypothesis that genetic variation contributes to variation in end‐point physiological traits, in this case galloping speed measured during field exercise tests. Standardisation of field‐measured phenotypes was attempted by assessing horses exercised on the same gallop track and managed under similar conditions by a single trainer. PCA of six key speed indices captured 73.9% of the variation with principal component 1 (PC1). Verifying the utility of the phenotype, we observed that PC1 (median) in 2‐year‐old horses was significantly different among elite, non‐elite and unraced horses (P < 0.001) and the temporal change with age in PC1 varied among horses with different myostatin (MSTN) g.66493737C>T SNP genotypes. A GWAS for PC1 in 2‐year‐old horses (n = 122) identified four SNPs reaching the suggestive threshold for association (P < 4.80 × 10−5), defining a 1.09 Mb candidate region on ECA8 containing the myosin XVIIIB (MYO18B) gene. In a GWAS for temporal change in PC1 with age (n = 168), five SNPs reached the suggestive threshold for association and defined candidate regions on ECA2 and ECA11. Both regions contained genes that are significantly differentially expressed in equine skeletal muscle in response to acute exercise and training stimuli, including MYO18A. As MYO18A plays a regulatory role in the skeletal muscle response to exercise, the identified genomic variation proximal to the myosin family genes may be important for the regulation of the response to exercise and training. [ABSTRACT FROM AUTHOR]

Summary: Background: Race distance aptitude in Thoroughbred horses is highly heritable and is influenced largely by variation at the myostatin gene (MSTN). Objectives: In addition to MSTN, we hypothesised that other modifying loci contribute to best race distance. Study design: Using 3006 Thoroughbreds, including 835 'elite' horses, which were >3 years old, had race records and were sampled from Europe/Middle‐East, Australia/New Zealand, North America and South Africa, we performed genome‐wide association (GWA) tests and separately developed a genomic prediction algorithm to comprehensively catalogue additive genetic variation contributing to best race distance. Methods: 48,896 single‐nucleotide polymorphism (SNP) genotypes were generated from high‐density SNP genotyping arrays. Heritability estimates, tests of GWA and genomic prediction models were derived for the phenotypes: average race distance, best race distance for elite, nonelite and all winning horses. Results: Heritability estimates were high (hm2 = 0.51, best race distance – elite; hm2 = 0.42, best race distance – nonelite; hm2 = 0.40, best race distance – all) and most of the variation was attributed to the MSTN gene. MSTN locus SNPs were the most strongly associated with the trait and included BIEC2‐438999 (ECA18:66913090; P = 4.51 × 10−110, average race distance; P = 2.33 × 10−42, best race distance – elite). The genomic prediction algorithm enabled the inclusion of variation from all SNPs in a model that partitioned horses into short and long cohorts following assignment of MSTN genotype. Additional genes with minor contributions to best race distance were identified. Main limitations: The nongenetic influence of owner/trainer decisions on placement of horses in suitable races could not be controlled. Conclusions: MSTN is the single most important genetic contributor to best race distance in the Thoroughbred. Employment of genetic prediction models will lead to more accurate placing of horses in races that are best suited to their inherited genetic potential for distance aptitude. [ABSTRACT FROM AUTHOR]

Summary: Durability traits in Thoroughbred horses are heritable, economically valuable and may affect horse welfare. The aims of this study were to test the hypotheses that (i) durability traits are heritable and (ii) genetic data may be used to predict a horse's potential to have a racecourse start. Heritability for the phenotype 'number of 2‐ and 3‐year‐old starts' was estimated to be hm2 = 0.11 ± 0.02 (n = 4499). A genome‐wide association study identified SNP contributions to the trait. The neurotrimin (NTM), opioid‐binding protein/cell adhesion molecule like (OPCML) and prolylcarboxypeptidase (PRCP) genes were identified as candidate genes associated with the trait. NTM functions in brain development and has been shown to have been selected during the domestication of the horse. PRCP is an established expression quantitative trait locus involved in the interaction between voluntary exercise and body composition in mice. We hypothesise that variation at these loci contributes to the motivation of the horse to exercise, which may influence its response to the demands of the training and racing environment. A random forest with mixed effects (RFME) model identified a set of SNPs that contributed to 24.7% of the heritable variation in the trait. In an independent validation set (n = 528 horses), the cohort with high genetic potential for a racecourse start had significantly fewer unraced horses (16% unraced) than did low (27% unraced) potential horses and had more favourable race outcomes among those that raced. Therefore, the information from SNPs included in the model may be used to predict horses with a greater chance of a racecourse start. [ABSTRACT FROM AUTHOR]

Summary: The Mongolian horse represents one of the most ancient extant horse populations. In this study we determined the male‐specific region of the Y chromosome (MSY) haplotype distribution in 60 Chinese Mongolian horses representing five distinct populations. Cosmopolitan male lineages were predominant in horses from one improved (Sanhe), one Chinese Mongolian subtype (Baicha Iron Hoof) and one indigenous (Abaga Black) population. In contrast, autochthonous Y chromosome diversity was evident among the two landrace populations (Wushen and Wuzhumuqin), as the majority of their MSY haplotypes were situated at root nodes in a network. Our results also suggest gene flow between Chinese Mongolian and Arabian horses, as an appreciable number of Wuzhumuqin horses carried haplotypes that are typically observed in Arabian horses. Although most horses carried modern haplotypes as a direct result of recent breed improvement, authentic Chinese Mongolian horses retain an ancient signature of paternal lineages that has not previously been described in extant horse populations. Therefore, further characterization of MSY variation in these populations will be important for the discovery of lost diversity in modern domestic horses and also for understanding the evolutionary history of equine paternal lineages. [ABSTRACT FROM AUTHOR]

Summary: Background: We hypothesised that grade/appearance for upper respiratory tract (URT) disorders identified at the first overground endoscopy (OGE) examination would vary at subsequent examinations. Objectives: To compare OGE examinations from horses evaluated on at least two occasions under similar exercise conditions without treatment intervention. Study design: Retrospective cohort. Methods: Pre‐exercise and exercising OGE recordings from Thoroughbred horses undergoing multiple examinations under similar exercise conditions were reviewed, with the first two recordings for each horse statistically evaluated. Paired Wilcoxon signed‐rank tests were used to assess differences in exercise and physiological parameters between examinations. Z‐tests were used to assess the proportion of changes in URT disorder grade/appearance between examinations. A McNemar's test was used to compare the proportion of horses with each disorder at each examination. Test–retest reliability across examinations was assessed using Spearman's ρ, and ordered logistic regression used to explore temporal effects on repeatability. Lattice plots were constructed to view variability in disorders over time. Results: Seventy‐eight horses (median age 2.4 years) with 195 resting endoscopic examinations including 72/78 horses with 179 pre‐exercise and exercising OGE examinations were evaluated. Median time between examinations was 226.5 days with no differences between exercise and physiological parameters. Grades significantly varied between examinations for all disorders, and in particular for palatal instability (PI) and epiglottic grade at rest. A temporal link between examination interval and disorder grade change was identified for PI and resting arytenoid asymmetry. Main limitations: OGE re‐examinations within a shorter, more consistent time‐frame would allow determination of intrahorse variability. The sample size was inadequate to conclusively establish temporal links between disorders and time between examinations. Conclusions: Variability for most URT abnormalities identified with OGE should be considered when making therapeutic decisions based on a single examination and may partially explain development of additional URT conditions after surgical intervention. The Summary is available in Portuguese ‐ see Supporting Information [ABSTRACT FROM AUTHOR]

Summary: Background: Endoscopic tip placement in the pharynx and water flushing interval (FI) may affect exercising upper respiratory tract (URT) endoscopic results. Objectives: To determine associations between the endoscopic tip position in the pharynx and automated FI with overground endoscopic (OGE) results. Study design: Randomised balanced 2X5 factorial design. Methods: A total of n = 200 horses undergoing OGE were randomly assigned into 10 groups (n = 20/group) of different automated endoscopic FIs (no flushing, 60, 120, 180, 240 s) with the endoscope tip positioned either rostrally (position A) or caudally (position B) in the pharynx. Endoscopic videos were analysed and all URT abnormalities graded using published scales. Disorders with ≤10% prevalence were excluded from the final analysis with only arytenoid asymmetry at exercise (AAex), vocal fold collapse (VFC), palatal dysfunction (PD) and medial deviation of the aryepiglottic folds (MDAF) included. The association of endoscope position and FI with URT disorders was assessed using ordinal regression models with P≤0.05 significant. Results: Endoscope tip positioning was significantly associated with PD grading (P = 0.002), with 63/100 horses diagnosed with PD in position A and 45/100 in position B. No other significant direct associations between URT disease and endoscope tip position were identified, although interactions between exercise velocity and endoscope position affected MDAF grade. FI was not directly associated with alterations in disorder grading, although interactions between exercise velocity and FI appeared to affect MDAF grade. Main limitations: The same horse was not evaluated under each test condition potentially resulting in sample bias. Interactions between disorders were not evaluated. The sample size was insufficient to conclusively explore relationships between all factors and disorder grading. Conclusions: Position of the endoscope tip within the pharynx appears to affect grading of PD during OGE examination. Exercise velocity may affect MDAF grade through interactions with endoscope position and FI. [ABSTRACT FROM AUTHOR]

Summary: Background: Conflicting results have been reported for risk factors for recurrent laryngeal neuropathy (RLN) based on resting endoscopic evaluation and comparison of single conformation traits, with many traits correlated to one another. Objectives: To simplify identification of signalment and conformation traits (i.e. variables) associated with RLN cases and controls diagnosed with exercising overground endoscopy (OGE) using exploratory factor analysis (EFA). Study design: Prospective cohort. Methods: Pearson's rank correlation was used to establish significance and association between variables collected from n = 188 Thoroughbreds from one stable by observers blinded to OGE results. Exploratory factor analysis was conducted on nine variables for cases and controls; common elements between variables developed a factor, with variables grouped into three factors for cases and controls respectively. Correlation (loading) between each variable and factor was calculated to rank relationships between variables and cases/controls, with factors retrospectively named based on their underlying correlations with variables. Results: Numerous inter‐correlations were present between variables. Most strongly correlated in cases were wither height with body weight (r = 0.70) and ventral neck length (r = 0.68) and in controls body weight with rostral neck circumference (r = 0.58). Wither height (r = 0.61) significantly loaded the top‐ranked factor for cases ('heightRLN'), explaining 25% of conformational variance. Ventral neck length (r = 0.69) and age (r = 0.57) significantly loaded the second‐ranked factor for cases ('neck lengthRLN'), explaining 16% of conformational variance. Rostral neck circumference (r = 0.86) and body weight (r = 0.6) significantly loaded the top‐ranked factor for controls ('body sizeCON'), explaining 19% of the variance. Wither height (r = 0.84) significantly loaded the second‐ranked factor for controls ('heightCON'), explaining 13% of the variance. Main limitations: Horses had not reached skeletal maturity. Conclusions: Exploratory factor analysis allowed weightings to be determined for each variable. Wither height was the predominant conformational feature associated with RLN. Exploratory factor analysis confirms aggregated conformational differences exist between RLN cases and controls, suitable for future evaluations. [ABSTRACT FROM AUTHOR]

Summary: Adaptation to early training and racing (i.e. precocity), which is highly variable in racing Thoroughbreds, has implications for the selection and training of horses. We hypothesised that precocity in Thoroughbred racehorses is heritable. Age at first sprint training session (work day), age at first race and age at best race were used as phenotypes to quantify precocity. Using high‐density SNP array data, additive SNP heritability ( h SNP 2) was estimated to be 0.17, 0.14 and 0.17 for the three traits respectively. In genome‐wide association studies (GWAS) for age at first race and age at best race, a 1.98‐Mb region on equine chromosome 18 (ECA18) was identified. The most significant association was with the myostatin (MSTN) g.66493737C>T SNP (P = 5.46 × 10−12 and P = 1.89 × 10−14 respectively). In addition, two SNPs on ECA1 (g.37770220G>A and g.37770305T>C) within the first intron of the serotonin receptor gene HTR7 were significantly associated with age at first race and age at best race. Although no significant associations were identified for age at first work day, the MSTN:g.66493737C>T SNP was among the top 20 SNPs in the GWAS (P = 3.98 × 10−5). Here we have identified variants with potential roles in early adaptation to training. Although there was an overlap in genes associated with precocity and distance aptitude (i.e. MSTN), the HTR7 variants were more strongly associated with precocity than with distance. Because HTR7 is closely related to the HTR1A gene, previously implicated in tractability in young Thoroughbreds, this suggests that behavioural traits may influence precocity. [ABSTRACT FROM AUTHOR]

Background Previous studies support good intra- and interobserver agreements for endoscopic evaluation of various upper respiratory tract ( URT) diseases in horses. However, these studies mainly assessed resting endoscopic examination videos and/or focussed on a single URT abnormality. Objectives To estimate intra- and interobserver agreement for identification and grading of all URT abnormalities from resting and overground endoscopy ( OGE) videos of Thoroughbreds. Study design Blinded, fully crossed design. Methods Resting and OGE URT videos for n = 43 Thoroughbreds were retrospectively chosen based on identification of common URT disorders. The videos were randomly evaluated in duplicate by 4 raters blinded to all information including prior URT disorder(s) diagnosis. Abnormalities were graded using well-described ordinal scales. Intra- and interobserver agreements were estimated using Cohen's weighted κ and Krippendorff's α, respectively. Results Intraobserver agreement was perfect/nearly perfect for arytenoid symmetry at exercise, epiglottic entrapment and epiglottic retroversion, substantial for arytenoid asymmetry at rest, palatal dysfunction ( PD), medial deviation of the aryepiglottic folds (MDAF), pharyngeal mucus and epiglottic grade at exercise and moderate for vocal fold collapse ( VFC), ventromedial luxation of the apex of the corniculate process of the arytenoid (VLAC), nasopharyngeal collapse ( NPC) and epiglottic grade at rest. Interobserver agreement was substantial for arytenoid symmetry at exercise and PD and moderate for arytenoid asymmetry at rest, MDAF, VLAC and epiglottic entrapment. It was only fair for VFC, epiglottic grade at exercise, epiglottic retroversion, pharyngeal mucus and NPC and poor for epiglottic grade at rest. Main limitations Sample size was insufficient to allow assessment of the effect of one abnormality on the grading of another abnormality. Conclusions Observers were consistent in grading URT disorders. However, significant disparity in grading existed between observers for some conditions affecting reliability. [ABSTRACT FROM AUTHOR]

Reasons for performing study Few noninvasive measures associated with performance assessment are available for racehorse trainers. Evaluation of body composition of superior human sprinters has revealed a lower fat mass ( FM), percentage (%) fat and greater fat-free mass ( FFM), but to date there have been few studies evaluating this in racehorses. Objectives To determine the effects of age, gender and training on body composition and the relationship between body composition, physiological measurements and performance in Thoroughbred racehorses. Methods At 2, 5 and 8 months of training, rump fat thickness ( RFT) was ultrasonographically measured in 1-, 2- and 3-year-old Thoroughbreds (n = 148), with FM, % fat and FFM calculated. Speed, heart rate, plasma lactate and serum creatine kinase concentrations were recorded during each fast work session. Training duration (number of training days) and intensity (number of fast work sessions) were collated for each training period. Retrospective racing performance was used to categorise horses as elite or nonelite. Results FFM was greater in males (P = 0.006) at all training stages. There were no interactions between training duration, intensity, gender and age (P>0.05); all effects were linear. Training duration had a negative effect on RFT (P = 0.0002), FM (P<0.0001) and % fat (P<0.0001) and a positive effect on FFM (P = 0.01). Training intensity had a negative effect on RFT (P = 0.009), FM (P<0.0001), % fat (P<0.0001) and FFM (P<0.0001). FFM was greater for elite vs. nonelite horses at all training stages (P = 0.003), for males (P = 0.05) and females (P = 0.04) and for 2- (P = 0.002) and 3-year-olds (P = 0.02). Conclusions While age and training affect body composition, FFM is associated with performance. Potential relevance Body composition assessment may assist fitness and performance evaluation. [ABSTRACT FROM AUTHOR]

Equine osteochondrosis is a developmental joint disease that is a significant source of morbidity affecting multiple breeds of horse. The genetic variants underlying osteochondrosis susceptibility have not been established. Here, we describe the results of a genome-wide association study of osteochondrosis using 90 cases and 111 controls from a population of Dutch Warmblood horses. We report putative associations between osteochondrosis and loci on chromosome 3 ( BIEC2-808543; P = 5.03 × 10−7) and chromosome 10 ( BIEC2-121323; P = 2.62 × 10−7). [ABSTRACT FROM AUTHOR]

To understand the origin and genetic diversity of Iranian native horses, mitochondrial DNA (mt DNA) D-loop sequences were generated for 95 horses from five breeds sampled in eight geographical locations in Iran. Sequence analysis of a 247-bp segment revealed a total of 27 haplotypes with 38 polymorphic sites. Twelve of 19 mt DNA haplogroups were identified in the samples. The most common haplotypes were found within haplogroup X2. Within-population haplotype and nucleotide diversities of the five breeds ranged from 0.838 ± 0.056 to 0.974 ± 0.022 and 0.011 ± 0.002 to 0.021 ± 0.001 respectively, indicating a relatively high genetic diversity in Iranian horses. The identification of several ancient sequences common between the breeds suggests that the lineage of the majority of Iranian horse breeds is old and obviously originated from a vast number of mares. We found in all native Iranian horse breeds lineages of the haplogroups D and K, which is concordant with the previous findings of Asian origins of these haplogroups. The presence of haplotypes E and K in our study also is consistent with a geographical west-east direction of increasing frequency of these haplotypes and a genetic fusion in Iranian horse breeds. [ABSTRACT FROM AUTHOR]

Our multidisciplinary study of historic Thoroughbred horses solves two long-running mysteries in racing history. Eclipse, the greatest racehorse ever known, never lost a race. His skeleton is housed in the Royal Veterinary College, London; however, there is controversy over its authenticity. The 1880 Epsom Derby was won by Bend Or. In one of the great controversies of Thoroughbred racing, the owners of Bend Or were accused of swapping him with another horse, Tadcaster, whose maternal pedigree was more prestigious. Bend Or's skeleton resides at the Natural History Museum, in London. Eclipse and Tadcaster were both extremely popular at stud, and the vast majority of racehorses today are descendents. We compared mitochondrial DNA haplotypes of living and historic Thoroughbred skeletons, including those of Eclipse and Bend Or. Additionally, we compared skeletal morphometrics of Eclipse's skeleton with measurements taken at autopsy. Carbon and nitrogen stable isotopes of a range of skeletal elements were compared in order to establish that the Eclipse skeleton was that of a single horse. Our multidisciplinary data suggest that the putative skeleton is consistent with that of Eclipse. In contrast, mitochondrial DNA haplotype sharing indicated that the skeleton known as Bend Or is most probably that of Tadcaster. [ABSTRACT FROM AUTHOR]

Summary Peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) has emerged as a critical control factor in skeletal muscle adaptation to exercise, acting via transcriptional control of genes responsible for angiogenesis, fatty acid oxidation, oxidative phosphorylation, mitochondrial biogenesis and muscle fibre type composition. In a previous study, we demonstrated a significant increase in mRNA expression for the gene encoding PGC-1α ( PPARGC1A) in Thoroughbred horse skeletal muscle following a single bout of endurance exercise. In this study, we investigated mRNA expression changes in genes encoding transcriptional coactivators of PGC-1α and genes that function upstream and downstream of PGC-1α in known canonical pathways. We used linear regression to determine the associations between PPARGC1A mRNA expression and expression of the selected panel of genes. Biopsy samples were obtained from the gluteus medius pre-exercise ( T0), immediately post-exercise ( T1) and 4 h post-exercise ( T2). Significant ( P < 0.05) expression fold change differences relative to T0 were detected for genes functioning in angiogenesis ( ANGP2 and VEGFA); Ca2+-dependent signalling pathway ( PPP3CA); carbohydrate/glucose metabolism ( PDK4); fatty acid metabolism/mitochondrial biogenesis ( PPPARGC1B); haem biosynthetic process ( ALAS1); insulin signalling ( FOXO1, PPPARGC1A and SLC2A4); mitogen-activated protein kinase signalling ( MAPK14 and MEF2A); and myogenesis ( HDAC9). Gene expression associations were identified between PPARGC1A and genes involved in angiogenesis, mitochondrial respiration, glucose transport, insulin signalling and transcriptional regulation. These results suggest that PGC-1α and genes regulated by PGC-1α play significant roles in the skeletal muscle response to exercise and therefore may contribute to performance potential in Thoroughbred horses. [ABSTRACT FROM AUTHOR]

Summary Using 1710 Thoroughbred racehorses in Japan, a cohort study was performed to evaluate the influence of genotypes at four single nucleotide polymorphisms (SNPs) on equine chromosome 18 (ECA18), which were associated in a previous genome-wide association study for racing performance with lifetime earnings and performance rank. In males, both g.65809482T>C and g.65868604G>T were related to performance rank ( P = 0.005). In females, g.65809482T>C ( P = 1.76E-6), g.65868604G>T ( P = 6.81E-6) and g.66493737C>T ( P = 4.42E-5) were strongly related to performance rank and also to lifetime earnings ( P < 0.05). When win-race distance (WRD) among all winning racehorses and best race distance (BRD) among elite racehorses were considered as the phenotypes, significant associations ( P < 0.001) were observed for all four SNPs. The favourable race distance of both elite (BRD) and novice racehorses (WRD) was also associated with genotypes in the ECA18 region, indicating the presence of a gene in this region influencing optimum race distance in Thoroughbred racehorses. Therefore, the association with performance rank is likely due to the bias in the race distances. The location of the SNPs within and proximal to the gene encoding myostatin ( MSTN) strongly suggests that regulation of the MSTN gene affects racing performance. In particular, the g.65809482T>C, g.65868604G>T and g.66493737C>T SNPs, or their combinations, may be genetic diagnostic markers for racing performance indicators such as WRD and BRD. [ABSTRACT FROM AUTHOR]

Athletic performance is influenced by a complex interplay among the environment and a suite of genes, which contributes to system-wide structure and function. In a panel of elite and non-elite Thoroughbred horses ( n = 148), we genotyped 68 SNPs in 17 putative exercise-relevant genes chosen from a genome scan for selection. We performed a series of case-control and quantitative association tests for relationships with racecourse performance. Thirteen SNPs in nine genes were significantly ( P < 0.05) associated with a performance phenotype. We selected five SNPs in four genes ( ACSS1, ACN9, COX4I1, PDK4) for validation in an independent sample set of elite and non-elite Thoroughbreds ( n = 130). Two SNPs in the PDK4 gene were validated ( P < 0.01) for associations with elite racing performance. When all samples were considered together ( n = 278), the PDK4_ 38973231 SNP was strongly associated ( P < 0.0005) with elite racing performance. Individuals with the A:A and A:G genotypes had a 16.2-16.6 lb advantage over G:G individuals in terms of handicap rating. Re-sequencing of the PDK4 gene and further genotyping will be required to identify the causative variant that is likely influencing exercise-induced variation in expression of the gene. Notwithstanding, this information may be employed as a marker for the selection of racehorses with the genetic potential for superior racing ability. [ABSTRACT FROM AUTHOR]

The recent completion of the horse genome and commercial availability of an equine SNP genotyping array has facilitated the mapping of disease genes. We report putative localization of the gene responsible for dwarfism, a trait in Friesian horses that is thought to have a recessive mode of inheritance, to a 2- MB region of chromosome 14 using just 10 affected animals and 10 controls. We successfully genotyped 34 429 SNPs that were tested for association with dwarfism using chi-square tests. The most significant SNP in our study, BIEC2-239376 ( P = 4.54 × 10, P = 7.74 × 10), is located close to a gene implicated in human dwarfism. Fine-mapping and resequencing analyses did not aid in further localization of the causative variant, and replication of our findings in independent sample sets will be necessary to confirm these results. [ABSTRACT FROM AUTHOR]

Summary Reasons for performing study: Fitness assessment can be challenging. The use of global positioning systems (GPS) with heart rate (HR) monitors has been promising; however, evaluation of speed parameters during training has not been reported. Objectives: To evaluate speed indices during training in Thoroughbreds using a GPS-HR monitor. Methods: Thoroughbreds (n = 102) were assessed during training with data collected each work day (WD; sprinting). Speed indices evaluated included maximal velocity (Vmax), duration at Vmax (Vmaxt), acceleration rate (m/s 2) from 800 m to Vmax (Acc800-Vmax), the distance (m) 6 (VmaxD6) and 12 (VmaxD12) s before (acceleration [a]) and after (deceleration [d]) Vmax and the deceleration rate from Vmax to the finish (VmaxDFd). Blood for plasma lactate ([LA]) and creatine kinase ([CK]) measurements were taken before (T0), 5 mins (T1) and 6 h after exercise (T2). WD accumulation, jockey, gallop condition, horse gender, age, total distance covered (DistT), maximum HR (HRmax), velocity at 200 beats/min (V200) and velocity at maximum HR (VHRmax) for each WD were evaluated for associations with [LA], [CK], speed indices and racing performance. Data were analysed by repeated measures ANOVA with P<0.05 significant. Results: No speed parameter clearly changed with training. Gallop condition affected Vmax, Vmaxt and all distances covered with Vmax and distances increasing and Vmaxt decreasing as gallop surface became firmer. Jockey influenced Vmax, VmaxD6a and all decelerations, while DistT was inversely associated with Acc800-Vmax, HRmax and V200 and positively associated with Vmax, all accelerations and decelerations. [LA] at T1 was positively associated with DistT and VmaxDFd. Conclusions: Speed parameters did not change with training but were affected by jockey, gallop condition and exercise distance. This information may help to modify training to maximise fitness, minimise injury and choose distances best suited for individuals. [ABSTRACT FROM AUTHOR]

Summary Reasons for performing study: The role of molecular signalling pathways in the phenotypic adaptation of skeletal muscle to different exercise stimuli in the Thoroughbred horse has not been reported previously. Objective: To examine CKM, COX4I1, COX4I2 and PDK4 gene expression following high intensity sprint and moderate intensity treadmill exercise stimuli in skeletal muscle of Thoroughbred horses. Materials and methods: Two groups of trained 3-year-old Thoroughbred horses participated. Group A (n = 6 females, n = 3 males) participated in an incremental step test (moderate intensity) to fatigue or HRmax on a Sato high speed treadmill (distance = 5418.67m ± 343.21). Group B (n = 8 females) participated in routine 'work' (sprint) on an all-weather gallop (distance = 812.83 m ± 12.53). Biopsy samples were obtained from the gluteus medius pre-exercise (T0), immediately post exercise (T1) and 4 h post exercise (T2). For physiological relevance venous blood samples were collected to measure plasma lactate and creatine kinase concentrations. Changes in mRNA expression were determined by quantitative real-time RT-PCR for creatine kinase muscle ( CKM), cytochrome c oxidase subunit IV isoform 1 ( COX4I1), cytochrome c oxidase subunit IV isoform 2 ( COX4I2) and pyruvate dehydrogenase kinase, isozyme 4 ( PDK4) genes. Statistical significance (α<0.05) was determined using Student's t tests. Results: COX4I2 mRNA expression decreased significantly in Group A and remained unchanged in Group B between T0 vs. T2 (−1.7-fold, P = 0.017; −1.0-fold, P = 0.859). PDK4 mRNA expression increased significantly in Group B but not in Group A between T0 vs. T1 (3.8-fold, P = 0.039; 1.4-fold, P = 0.591). There were no significant changes in the expression in CKM or COX4I1 mRNA abundance in either group. Conclusions: Different exercise protocols elicit variable transcriptional responses in key exercise relevant genes in equine skeletal muscle due to variation in metabolic demand. [ABSTRACT FROM AUTHOR]

Summary Reasons for performing study: The wild progenitors of the domestic horse were subject to natural selection for speed and stamina for millennia. Uniquely, this process has been augmented in Thoroughbreds, which have undergone at least 3 centuries of intense artificial selection for athletic phenotypes. While the phenotypic adaptations to exercise are well described, only a small number of the underlying genetic variants contributing to these phenotypes have been reported. Objectives: A panel of candidate performance-related genes was examined for DNA sequence variation in Thoroughbreds and the association with racecourse performance investigated. Materials and methods: Eighteen candidate genes were chosen for their putative roles in exercise. Re-sequencing in Thoroughbred samples was successful for primer sets in 13 of these genes. SNPs identified in this study and from the EquCab2.0 SNP database were genotyped in 2 sets of Thoroughbred samples (n = 150 and 148) and a series of population-based case-control investigations were performed by separating the samples into discrete cohorts on the basis of retrospective racecourse performance. Results: Twenty novel SNPs were detected in 3 genes: ACTN3, CKM and COX4I2. Genotype frequency distributions for 3 SNPs in CKM and COX4I2 were significantly (P<0.05) different between elite Thoroughbreds and racehorses that had never won a race. These associations were not validated when an additional (n = 130) independent set of samples was genotyped, but when analyses included all samples (n = 278) the significance of association at COX4I2 g.22684390C>T was confirmed (P<0.02). Conclusions: While molecular genetic information has the potential to become a powerful tool to make improved decisions in horse industries, it is vital that rigour is applied to studies generating these data and that adequate and appropriate sample sets, particularly for independent replication, are used. [ABSTRACT FROM AUTHOR]

Equine mitochondrial DNA sequence variation was investigated in three indigenous Irish horse populations (Irish Draught Horse, Kerry Bog Pony and Connemara Pony) and, for context, in 69 other horse populations. There was no evidence of Irish Draught Horse or Connemara Pony sequence clustering, although the majority of Irish Draught Horse sequences (47%) were assigned to haplogroup D. Conversely, 31% of the Kerry Bog Pony sequences were assigned to the rare haplogroup E. In addition to the extant population analyses, ancient DNA sequences were generated from three out of four Irish archaeological specimens, all of which were assigned to haplogroup A. [ABSTRACT FROM AUTHOR]

Equine mitochondrial DNA (mtDNA) phylogeny reconstruction reveals a complex pattern of variation unlike that seen in other large domesticates. It is likely that this pattern reflects a process of multiple and repeated, although not necessarily independent, domestication events. Until now, no clear geographic affiliation of clades has been apparent. In this study,amova analyses have revealed a significant non-random distribution of the diversity among equine populations when seven newly sequenced Eurasian populations were examined in the context of previously published sequences. The association of Eastern mtDNA types in haplogroup F was highly significant using Fisher's exact test of independence ( P = 0.00000). For the first time, clear biogeographic partitioning has been detected in equine mtDNA sequence. [ABSTRACT FROM AUTHOR]

Mitochondrial DNA (mtDNA) D-loop sequences (381 bp) from 100 thoroughbreds in 19 of the most common matrilineal female families were used to reconstruct a founder female population for the thoroughbred (∼1650–1750 AD). Seventeen haplotypes were found to have contributed to the 19 female lineages. In order to place the reconstructed founder population in wider historical context, we examined, using both single strand conformation polymorphism and direct sequence analysis, variation in a 343 bp mtDNA fragment in that population and 13 other horse populations of disparate provenance. Interpopulation diversity analyses revealed no significant difference in variation between the thoroughbred founder population and the 13 other diverse horse populations and suggested a non-random partitioning of diversity among geographically diverse horse populations. Within thoroughbreds, almost half of the female families, which are each considered from pedigrees to have matrilines converging to one of >30 historically recognized female ancestors, contained sequences which were inconsistent with common descent. Examination of the anomalies in the context of pedigree records suggests the majority might be best explained as confusion of mares at the foundation stages, although some could have some bearing on more recent (19th century – 1980) lineages. We have used this combination of molecular and historical information to identify some of the founder dams and to make new interpretations about the early history of the thoroughbred. [ABSTRACT FROM AUTHOR]

A justification is offered for using micro-computers and specially-designed programs with severely visually impaired pre-school children. It is argued that this technology optimizes the visual environment for the child and provides immediate feedback about the correctness of his responses to the stimuli displayed on the screen. Some of the problems encountered in such use are described, with examples taken from sessions in which teachers are working with children as young as 2 years of age, using teaching/learning sequences designed to promote and exercise visual perception skills. Among the issues addressed are the nature of the language interactions between child and adult, the effects of altering the complexity of the tasks, and the possible value of formal task analysis as a means of enabling the teacher to pinpoint critical stages in the learning process. [ABSTRACT FROM AUTHOR]

Studies the convenient detection of single nucleotide polymorphism haplotypes in the bovine growth hormone gene using amplification-created restriction sites. Characteristics of growth hormone; Amplification created restriction sites design, polymerase chain reaction and single nucleotide polymorphism genotyping; Haplotype network construction.