Exposure of horses to high concentrations of ammonia gas might cause inflammation of the cuticle tunica mucosa of the respiratory tract [7]. We studied the effect on the reduction of ammonia gas concentration when a bag to collect excreta (“the Equine Nappy”) was fitted to penned horses, and additionally examined the influence of ammonia exposure on hay and water intake. Three healthy stallions were used in the study and a comparison was made over 48 hr between wearing the diaper (Diapper) and without the diaper (Control). In Control’s pens, the concentration of ammonia gas rose to more than 4.0 ppm after 42 hr, whereas in the diaper pens, the concentration was maintained at less than 1.0 ppm after 48 hr. After 6 hr, in the presence of high ammonia gas concentrations, the hay intake of the controls decreased. We concluded that fitting the diaper effectively decreased exposure of horses to ammonia gas, helped keep the horse good health, and in addition lowered the cost of bedding.

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Laryngeal Hemiplegia (LH) leads to a reduction in performance and because of it many promising racehorses have been forced to end their racing career. Therefore it is important for breeding good racehorses to estimate the heritability of LH. In this study, the computer program was developed based on the Bayesian analysis with Gibbs sampling for estimating the heritability of categorical traits assuming liability. A total of 706 records with LH-grade in Thoroughbreds aged 2 to 5 years were assigned for the genetic analysis. LH-grades consisted of five severity classes from 0 to 4. Racehorse breeders are often interested in whether the genetic effect controlling a complex disorder is present in the population. To answer this question, the binary trait analysis would be also useful. The heritability of LH-grade in the Thoroughbred horse was then also estimated as a binary or as a categorical trait. The mode values of the posterior distributions of heritability were 0.23 and 0.20 for the binary and the categorical trait, respectively. The fact that in the Thoroughbred population studied LH is at least partially controlled by genetic factors leads to the suggestion that when applying adequate breeding measures the prevalence of LH will be able to be reduced.

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Sixteen strains of Salmonella enterica serotype Typhimurium (S. Typhimurium) isolated from foals from 1981 until 1996 in Hokkaido Prefecture, Japan, were examined for their biotype, drug resistance, plasmid profile, virulence plasmid, and virulence in mice and foals. Nine strains isolated from Thoroughbred foals in Hidaka district in 1981 were shown to possess similar properties. Likewise, two strains isolated from crossbred foals in a farm in Sorachi district in 1996, although distinct from the Hidaka isolates, were similar to one another. These 11 strains were all shown to contain a virulence plasmid, and to be virulent in mice and foals. However, five other strains isolated from Thoroughbred foals that were bred in different farms in Hidaka between 1990 and 1993 demonstrated variable properties, and did not possess the virulence plasmid nor show virulence in mice. Thus it was suggested that large outbreaks of S. Typhimurium infection in foals were more likely to be caused by virulent strains possessing the virulence plasmid, although sporadic infections may also be caused by non-virulent S. Typhimurium.

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We investigated whether gender and racing performance of Thoroughbred racehorses affected the relationship between the heart rate and running speed. Twenty well-trained Thoroughbred racehorses, 7 “open” horses (3 males and 4 females) and 13 “non-open” horses (3 males and 10 females), in JRA Ritto Training Center were used in this study. When the horses cantered around the 500 m circular dirt course at submaximal speed, lap times were measured to calculate mean running speed. Heart rates of the horses were recorded on heart rate monitors during exercise. There was a significant difference in the heart rates between male and female horses (p<0.05). On racing performance, there was a tendency for heart rates to be lower in “open” horses (p=0.11). These results suggest that the aerobic capacity of male horses may be higher.

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T. M. Opera O is considered as one of the greatest racehorses in the history of horseracing in Japan. Only a very few data is available on circulatory function of elite Thoroughbred racehorses. Recently, we obtained data on circulatory parameters of T. M. Opera O. The left ventricular mass of T. M. Opera O, as measured on an echocardiogram, was 4.60 kg. The resting heart rate (HR) of T. M. Opera O was 25 beat/min. The low-frequency and high-frequency power, as determined by an analysis of HR variability, were 13,900 and 5.963 ms², respectively, which were considerably higher than those of the other racehorses. These results suggest that a large heart, formed by genetic factors and training, markedly enhanced the parasympathetic nervous activity and reduced the resting HR of T. M. Opera O. The data we obtained from T. M. Opera O is invaluable for understanding the physical fitness of elite Thoroughbreds and for further developing their athletic performance.

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