Metabolic response to standardised exercise test in standardbred trotters with red cell hypervolaemia

Origin and spread of Thoroughbred racehorses inferred from complete mitochondrial genome sequences: Phylogenomic and Bayesian coalescent perspectives

The Thoroughbred horse breed was developed primarily for racing, and has a significant contribution to the qualitative improvement of many other horse breeds. Despite the importance of Thoroughbred racehorses in historical, cultural, and economical viewpoints, there was no temporal and spatial dynamics of them using the mitogenome sequences. To explore this topic, the complete mitochondrial genome sequences of 14 Thoroughbreds and two Przewalski’s horses were determined. These sequences were analyzed together along with 151 previously published horse mitochondrial genomes from a range of breeds across the globe using a Bayesian coalescent approach as well as Bayesian inference and maximum likelihood methods. The racing horses were revealed to have multiple maternal origins and to be closely related to horses from one Asian, two Middle Eastern, and five European breeds. Thoroughbred horse breed was not directly related to the Przewalski’s horse which has been regarded as the closest taxon to the all domestic horses and the only true wild horse species left in the world. Our phylogenomic analyses also supported that there was no apparent correlation between geographic origin or breed and the evolution of global horses. The most recent common ancestor of the Thoroughbreds lived approximately 8,100–111,500 years ago, which was significantly younger than the most recent common ancestor of modern horses (0.7286 My). Bayesian skyline plot revealed that the population expansion of modern horses, including Thoroughbreds, occurred approximately 5,500–11,000 years ago, which coincide with the start of domestication. This is the first phylogenomic study on the Thoroughbred racehorse in association with its spatio-temporal dynamics. The database and genetic history information of Thoroughbred mitogenomes obtained from the present study provide useful information for future horse improvement projects, as well as for the study of horse genomics, conservation, and in association with its geographical distribution.

The effect of repeated barrel racing on blood biomarkers and physiological parameters in Quarter Horses

The objective of this study was to evaluate barrel horses undergoing a field test with one repetition. Quarter-Horses were used (14 males and females; average age: 6.5 years old), and they ran two times for 5 min in the same field. Six different periods were evaluated: rest (T-0), immediately after the first (T-1) and second races (T-2), and after 15 (T-15), 30 (T-30) and 240 min (T-240) of recovery. Heart rate (HR), speed, distance and duration were measured using a HR monitor with GPS during the races. Blood was collected to determinate glucose, lactate, total proteins (TP), albumin, globulin, urea, creatinine, uric acid (UA), triglycerides, cholesterol, non-esterified fatty acids (NEFA), gammaglutamyltransferase (GGT), creatine kinase (CK), and cortisol concentrations, as well as to perform a haemogram. The results were analysed using ANOVA and Tukey’s tests using a P-value of 5%, and they showed a maximum HR>200 bpm after both races. The largest %HR>>170 bpm occurred in the second race (P<0.05). Glucose and lactate concentrations were elevated at T-2 (P<0.05). TP, creatinine, UA and triglycerides concentrations remained elevated at T-1, T-2 and T-30 (P<0.05). TP and creatinine concentrations returned to basal concentrations at T-30 (P>0.05), and UA and triglycerides returned to base concentrations at T-240 (P>0.05). NEFA, cholesterol, GGT and CK concentrations did not change (P>0.05). Cortisol concentrations were higher at T-2 (P<0.05) but at T-240 were similar to T-0 (P>0.05). Red blood cell concentrations and haematocrits had higher values after the second race (P<0.05). These results showed that barrel horses had intense exercise and that two races with a short rest interval between them produced similar metabolic and physiologic adaptations between races, showing that the proposed protocol may be a useful tool for field characterisation of horses’ training and may contribute to the implementation of adequate training and nutritional programs.

Association of low race performance with mtDNA haplogroup L3b of Australian thoroughbred horses

Mitochondrial DNA (mtDNA) encodes the genes for respiratory chain sub-units that determine the efficiency of oxidative phosphorylation in mitochondria. The aim of this study was to determine if there were any haplogroups and variants in mtDNA that could be associated with athletic performance of Thoroughbred horses. The whole mitochondrial genomes of 53 maternally unrelated Australian Thoroughbred horses were sequenced and an association study was performed with the competition histories of 1123 horses within their maternal lineages. A horse mtDNA phylogenetic tree was constructed based on a total of 195 sequences (including 142 from previous reports). The association analysis showed that the sample groups with poor racing performance history were enriched in haplogroup L3b (p = .0003) and its sub-haplogroup L3b1a (p = .0007), while those that had elite performance appeared to be not significantly associated with haplogroups G2 and L3a1a1a (p > .05). Haplogroup L3b and L3b1a bear two and five specific variants of which variant T1458C (site 345 in 16s rRNA) is the only potential functional variant. Furthermore, secondary reconstruction of 16s RNA showed considerable differences between two types of 16s RNA molecules (with and without T1458C), indicating a potential functional effect. The results suggested that haplogroup L3b, could have a negative association with elite performance. The T1458C mutation harboured in haplogroup L3b could have a functional effect that is related to poor athletic performance.

Potential role of maternal lineage in the thoroughbred breeding strategy

Many studies have focused on identifying the genes or single nucleotide polymorphisms associated with the athletic ability of thoroughbreds, but few have considered differences in maternal and paternal heritability of athletic ability. Herein, we report on our association study of career race performances of 675 Australian thoroughbreds with their pedigrees. Racing performance data (prize money per start) were collected from the Bloodhound database. The performance of all horses was categorised as either poor or elite athletic achievement. Then, 675 foals were divided by their parents' performance (elite or poor) into four groups: (1) elite dams and elite sires; (2) elite dams and poor sires; (3) poor dams and elite sires; and (4) poor dams and poor sires. The performance of foals was then compared between the four groups. The results show that the heritability of race performance between dams and foals (r = 0.141, P < 0.001) is much higher than that between sires and foals (r = 0.035, P = 0.366), and that this difference is statistically significant (P < 0.05). We also examined the effect of the child-bearing age of dams and sires on the ratio of elite foals. We found a strong correlation between the number of elite foals and dams' child-bearing age (r = -0.105, P < 0.001), with the ratio of elite offspring reaching a high level between a child-bearing age of 8 and 11 years (χ2 = 14.31, d.f. = 1, P < 0.001). These findings suggest that the maternal line may play an important role in the selective breeding of athletic performance in thoroughbreds.

Quantification of the energy expenditure during training exercises in Standardbred trotters

An appropriate energy feeding management that ensures the optimal dietary energy supply according to the energy expenditure (EE) is a crucial component for the horse's performance. The main purpose of this study was to determine the EE during four specific exercises used in the training of Standardbred trotters (promenade, jogging, parcours and interval work-outs). A total of six Standardbred geldings performed four different testing situations on a track. The intensity (expressed in percentage of the maximal velocity over 500 m, i.e. v500) and volume (distance and duration) of the testing situations were determined according to practices reported by French trainers. Promenade and jogging included only an exercise phase, whereas parcours and interval situations also included a warm-up and a recovery phase. Oxygen uptake (VO2), carbon dioxide production (VCO2) and heart rate (HR) were continuously recorded from 2 min before the beginning through to the end of the testing situations, using a portable respiratory gas analyser. Blood lactate levels and rectal temperature were determined before and immediately after the exercise phase of each testing situations. EE of the different phases (warm-up, exercise and recovery) and EE of the entire testing situations (EETOTAL) were calculated from VO2 measurements and the O2 caloric equivalent. Interval and parcours situations induced higher physiological responses than promenade and jogging situations, particularly in terms of VO2peak, VCO2peak and HRpeak. The highest blood lactate concentration (6 mmol/l) was measured after the interval exercise, and respiratory exchange ratios ⩾1 were observed only for the parcours situation. The EE of exercise phase varied from 0.49 to 1.79 kJ/min per kg for promenade and parcours situations. The EE of warm-up and recovery phases did not differ between parcours and interval situations, and was estimated at 1.04 and 0.57 kJ/min per kg BW, respectively. On average, the warm-up and the recovery phases contributed to 38% and 19% of the EETOTAL. For promenade, jogging, parcours and interval situations, EETOTAL was evaluated at 12 618, 11 119, 13 698 and 18 119 kJ, respectively.

Molecular Characterization and Expression Analysis of Equine Vascular Endothelial Growth Factor Alpha (VEGFα) Gene in Horse (Equus caballus)

The objective of this study was to determine the molecular characteristics of the horse vascular endothelial growth factor alpha gene (VEGFα) by constructing a phylogenetic tree, and to investigate gene expression profiles in tissues and blood leukocytes after exercise for development of suitable biomarkers. Using published amino acid sequences of other vertebrate species (human, chimpanzee, mouse, rat, cow, pig, chicken and dog), we constructed a phylogenetic tree which showed that equine VEGFα belonged to the same clade of the pig VEGFα. Analysis for synonymous (Ks) and non-synonymous substitution ratios (Ka) revealed that the horse VEGFα underwent positive selection. RNA was extracted from blood samples before and after exercise and different tissue samples of three horses. Expression analyses using reverse transcription-polymerase chain reaction (RT-PCR) and quantitative-polymerase chain reaction (qPCR) showed ubiquitous expression of VEGFα mRNA in skeletal muscle, kidney, thyroid, lung, appendix, colon, spinal cord, and heart tissues. Analysis of differential expression of VEGFα gene in blood leukocytes after exercise indicated a unimodal pattern. These results will be useful in developing biomarkers that can predict the recovery capacity of racing horses.

Hematologia e bioquímica sérica de equinos de concurso completo de equitação em treinamento

Avaliaram-se a hematologia e a bioquímica sérica em equinos de concurso completo de equitação (CCE) em treinamento durante testes de esforço incremental em esteira ergométrica de alta velocidade. Foram utilizados 16 equinos em delineamento experimental inteiramente ao acaso com quatro tratamentos e quatro repetições em esquema de parcelas subdivididas, utilizando-se como fontes de variação nos tratamentos a idade e o histórico de treinamento em CCE. As parcelas foram constituídas pelos testes incrementais realizados nas fases inicial e final do treinamento. As subparcelas foram representadas pelos tempos de avaliação e coletas. Os equinos do grupo experimental novos iniciantes apresentaram valor médio do hematócrito de 43,24%, sendo inferior ao hematócrito do grupo adultos iniciantes, 45,63%, novos experientes, 46,39%, e competidores, 47,74%. Houve diferença (P<0,05) entre os testes físicos realizados nas fases inicial e final do treinamento, com redução na concentração plasmática de glicose, de 112 para 98,88mg/dL, nas concentrações séricas de creatinina, de 1,41 para 1,29mg/dL, e de proteínas totais, de 6,52 para 6,38g/dL, na contagem de monócitos, de 0,54 para 0,48 10³/mm³, e com aumento na concentração plasmática de lactato, de 3,31 para 3,79mmol/L, na concentração sérica de ácido úrico, de 1,44 para 1,77mg/dL, no hematócrito, de 44,19 para 46,90%, na concentração de hemoglobina, de 14,33 para 15,10g/dL, e na contagem de leucócitos totais, de 9,26 para 9,61 10³/mm³. O treinamento dos equinos de CCE aumentou o condicionamento físico dos equinos, com maior capacidade de metabolização do lactato após o exercício e aumento nos valores basais do hematócrito e da concentração de hemoglobina.

Changes in intramuscular amino acid levels in submaximally exercised horses - a pilot study

The time-dependent changes in intramuscular amino acid (AA) levels caused by exercise and by feeding a protein/AA supplement were analysed in nine horses. Horses were submitted to a total of four standardized exercise tests (SETs). Amino acid concentrations were determined prior to, immediately after, 4 and 18 h after exercise. The experiment was subdivided into two consecutive periods of 3 weeks. In each period two SETs were performed. In the second period, horses were given a protein/AA supplement within 1 h after exercise. Significant changes in mean plasma AA levels similar to previous studies were noted to be time-dependent and to be associated with feeding the supplement. The intramuscular concentrations of the free AA in relation to pre-exercise levels showed significant time-dependent changes for alanine, asparagine, aspartate, citrulline, glutamine, glycine, isoleucine, leucine, methionine, serine, taurine, threonine, tyrosine and valine. Feeding the supplement significantly increased the 4 h post-exercise intramuscular concentration of alanine, isoleucine, methionine and tyrosine. At 18 h after exercise, apart from isoleucine and methionine, levels were still increased and also those of asparagine, histidine and valine in relation to none treatment. Hence, it was concluded that AA mixtures administered orally to horses within 1 h after exercise increased intramuscular AA pool.

A genome scan for positive selection in thoroughbred horses

Thoroughbred horses have been selected for exceptional racing performance resulting in system-wide structural and functional adaptations contributing to elite athletic phenotypes. Because selection has been recent and intense in a closed population that stems from a small number of founder animals Thoroughbreds represent a unique population within which to identify genomic contributions to exercise-related traits. Employing a population genetics-based hitchhiking mapping approach we performed a genome scan using 394 autosomal and X chromosome microsatellite loci and identified positively selected loci in the extreme tail-ends of the empirical distributions for (1) deviations from expected heterozygosity (Ewens-Watterson test) in Thoroughbred (n = 112) and (2) global differentiation among four geographically diverse horse populations (F(ST)). We found positively selected genomic regions in Thoroughbred enriched for phosphoinositide-mediated signalling (3.2-fold enrichment; P<0.01), insulin receptor signalling (5.0-fold enrichment; P<0.01) and lipid transport (2.2-fold enrichment; P<0.05) genes. We found a significant overrepresentation of sarcoglycan complex (11.1-fold enrichment; P<0.05) and focal adhesion pathway (1.9-fold enrichment; P<0.01) genes highlighting the role for muscle strength and integrity in the Thoroughbred athletic phenotype. We report for the first time candidate athletic-performance genes within regions targeted by selection in Thoroughbred horses that are principally responsible for fatty acid oxidation, increased insulin sensitivity and muscle strength: ACSS1 (acyl-CoA synthetase short-chain family member 1), ACTA1 (actin, alpha 1, skeletal muscle), ACTN2 (actinin, alpha 2), ADHFE1 (alcohol dehydrogenase, iron containing, 1), MTFR1 (mitochondrial fission regulator 1), PDK4 (pyruvate dehydrogenase kinase, isozyme 4) and TNC (tenascin C). Understanding the genetic basis for exercise adaptation will be crucial for the identification of genes within the complex molecular networks underlying obesity and its consequential pathologies, such as type 2 diabetes. Therefore, we propose Thoroughbred as a novel in vivo large animal model for understanding molecular protection against metabolic disease.

Distribution of monocarboxylate transporter isoforms MCT1, MCT2 and MCT4 in porcine muscles

AIM

Monocarboxylate transporters (MCT), which cotransport lactate anions and protons across cell membranes, are important for regulation of muscle pH. We measured amounts of MCT1, MCT2 and MCT4 by immunoblotting in five different porcine muscles, to study MCT-isoform distribution both in oxidative and highly glycolytic muscles.

METHODS

Samples from the longissimus dorsi, gluteus superficialis, semimembranosus, infraspinatus and masseter were taken from 18 slaughtered pigs.

RESULTS

Oxidative capacity, estimated on the basis of the activities of lactate dehydrogenase (LDH), citrate synthase (CS) and 3-OH-acyl-CoA dehydrogenase (HAD), was highest in the infraspinatus and masseter, and was very low in the gluteus, semimembranosus and longissimus dorsi. In all muscles, the amount of MCT1 was small but variable. The amount of MCT2 was more abundant in the glycolytic than in the oxidative muscles, while MCT4 was found in equal amounts in all muscles. MCT2, but not MCT4, correlated negatively with CS and HAD.

CONCLUSIONS

The results together with measured concentrations of lactate suggest that MCT2 may function as the housekeeping lactate transporter, preventing acidification especially in highly glycolytic muscles in which the capacity to oxidize lactate is low. The results also support the view that, as in other species, MCT4 would be important at high lactate concentrations that occur during stress.

Metabolic and hormonal changes after exercise in relation to muscle glycogen concentrations

To test whether, in horses, the concentration of muscle glycogen can be influenced by increasing the uptake of glucose into the muscle cells or by providing a gluconeogenic precursor, 9 trained half-bred riding horses performed on a treadmill a 1.5 h competition exercise test (CET). Each horse performed CET 3 times and 30 min after CET, each was given one of the following solutions: isotonic glucose-electrolyte (GE) solution, GE supplemented with 50 g leucine (GEL) to increase insulin secretion, or GE supplemented with 200 ml propionic acid (GEP), a gluconeogenic precursor. Administration of GE solutions caused no increase in plasma glucose concentration. The highest concentration of insulin was measured after GEL, but also in the GE group the concentration of insulin increased. GEP completely inhibited the increase in insulin concentration. Concentration of glucagon was increased 6 and 22.5 h after CET. None of the post exercise treatments influenced significantly the glycogen content at 22.5 h after CET. This indicates that neither i) elevation of insulin concentration to increase muscle-uptake of glucose, nor ii) increase in the availability of a glucose precursor, propionic acid, was able to increase accumulation of glycogen in the middle gluteal muscle.