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ABSTRACT. Myostatin is a member of the transforming growth factor- family with a key role in inhibition of muscle growth by negative regulation of both myoblast proliferation and differentiation. Recently, a genomic region on ECA18, which includes the MSTN gene, was identified as a candidate region influencing racing performance in Thoroughbreds. In this study, four SNPs on ECA18, g.65809482T>C, g.65868604G>T, g.66493737C>T, and g.66539967A>G, were genotyped in 91 Thoroughbred horses-in-training to evaluate the association between genotype and body composition traits, including body weight, withers height, chest circumference, cannon circumference, and body weight/withers height. Of these, statistically differences in body weight and body weight/withers height were associated with specific genotypes in males. Specifically, body weight/withers height showed statistically significant differences depending on genotype at g.658604G>T, g.66493737C>T, and g.66539967A>G (P<0.01) in males during the training period. Animals with a genotype associated with suitability for short-distance racing, C/C at g.66493737C>T, had the highest value (3.17  0.05 kg·cm -1 ) for body weight/withers height in March, while those with a genotype associated with suitability for long-distance racing, T/T, had the lowest (2.99  0.03 kg·cm -1 ). In females, the trends in the association of body weight/withers height with genotypes were similar to those observed in males. As the SNPs are not believed to be linked to coding variants in MSTN, these results suggest that regulation of MSTN gene expression influences skeletal muscle mass and hence racing performance, particularly optimum race distance, in Thoroughbred horses.KEY WORDS: body composition, myostatin, racing performance, Thoroughbred.J. Vet. Med. Sci. 73(12): 1617-1624 Thoroughbred horses originated from a small number of Arab, Barb, and Turk stallions and native British mares approximately 300 years ago [3,5,12]. Since then, they have been selectively bred to improve speed and stamina, and are consequently superior competitive racehorses. As a result, Thoroughbred horses have a very high skeletal muscle mass comprising over 55% of total body mass [10] ) is also superior to that of other species of similar size [16,17,26]. Such traits have been enhanced by artificial selection for the DNA sequence variants contributing to exceptional racing performance [8].Many significant advances have been made in the horse genome project (http://www.uky.edu/Ag/Horsemap/welcome.html), such as the completion of a high-quality draft horse genome sequence with over 1.1 million identified SNPs [25]. The advances in the genetic infrastructure for the horse has enabled the identification of a genomic region on ECA18 associated with racing performance phenotypes. Four case-control studies, including a candidate gene study [13], a microsatellite-based genome-wide association study [23], and two genome-wide SNP association studies [2,14] have identified the same genomic region on ECA18 as associated with r...

It has not been common to perform regular ultrasound examination of the fetus in equine practice, due to the increasing volume of the uterus caused by fetal development. The convex three-dimensional transducer is bulb-shaped and is able to observe wide areas. In addition, its operation is simple, making it easy to create appropriate angles for various indices using a transrectal approach. The aim of this study was to measure Thoroughbred fetal growth indices throughout gestation using a convex transducer and to clarify the detectable period of some indices for clinical use. We demonstrated changes in fetal indices, such as crown rump length (CRL), fetal heart rate (FHR), fetal eye and kidney and the combined thickness of uterus and placenta (CTUP). CTUP increased from 30 weeks of gestation, and FHR peaked at 8 weeks and then decreased to term. CRL could be observed until 13 weeks due to its wide angle, longer than in previous reports. Fetal eye and kidney could be observed from 10 and 28 weeks, respectively, and these increased with pregnancy progress. The present results showed the advantage of transrectal examination using a convex transducer for evaluation of normal fetal development. Although ultrasonographic examination in mid- to late-gestation is not common in equine reproductive practice, our comprehensive results would be a useful basis for equine pregnancy examination.

This study aimed to compare body growth, metabolic, and reproductive hormonal changes in trained Thoroughbred yearling horses under different climate conditions with and without light supplementation (LS). Thoroughbred yearlings raised at research centers of the Japan Racing Association in Hokkaido (north) or Miyazaki (south) were divided into control and LS groups. In the LS groups, 44 colts and 47 fillies from Hokkaido and 11 colts and 11 fillies from Miyazaki were exposed to LS with an extended photoperiod of 14.5 hr of daylight and 9.5 hr of darkness. One week before and once a month after LS, circulating total thyroxine (T4), insulin-like growth factor-I (IGF-1), prolactin (PRL), cortisol, and progesterone (P4) concentrations were measured by radioimmunoassay and fluoroimmunoassay, respectively. Growth parameters, including body weight, height, girth, and cannon bone circumferences, were measured monthly. Hair coat (HC) condition was scored. Under natural conditions, the T4 concentrations of Hokkaido yearlings tended to be higher, whereas the IGF-1 (colt) and PRL levels were significantly lower than those of yearlings in Miyazaki. Growth parameters and HC scores were lower in Hokkaido yearlings. With LS, the PRL and P4 concentrations in Hokkaido and Miyazaki were higher, and the first ovarian activity tended to be earlier than in the controls. Only LS Hokkaido yearlings showed significantly higher HC scores than the controls. Comparing the different climates among the LS yearlings, the levels of PRL and P4 and the HC scores in Hokkaido yearlings increased and reached levels similar to those in Miyazaki yearlings. The body weight and girth increment percentages of Hokkaido yearlings in January dramatically decreased and then eventually increased to levels similar to those of Miyazaki yearlings. This suggested that yearlings in naturally colder Hokkaido exhibit higher basal metabolism to maintain homeostasis. However, providing LS may help to improve growth and early development of reproductive function in Hokkaido yearlings to levels equal to those of Miyazaki horses.

ABSTRACT. Prevalence of equine gastric ulcer syndrome in 85 young Thoroughbreds was investigated. The presence of gastric ulcers was confirmed in 27.1% (23/85) of the horses by endoscopic examination. Sixty-two horses without gastric ulcers were allocated randomly to either the treated group (31 horses) or sham-dosed control group (31 horses) in order to investigate the efficacy of omeprazole oral paste in the prevention of gastric ulcers. At the second endoscopic examination conducted after 28 days of administration, only 1 horse in the treated group developed gastric ulcers, while 12 horses developed gastric ulcers in the control group. Based on these data, the efficacy of omeprazole in prevention of equine gastric ulcers in young Thoroughbreds during the training period was confirmed.