A relatively large scale epizootic of equine viral arteritis (EVA) which occurred in Thoroughbreds at Arlington Park Race Course in the USA in 1993 , just after the first outbreak of EVA in non-Thoroughbreds in the United Kingdom [40, 95] remains vivid in our memory. It had been considered that the United Kingdom, Ireland, Australia, New Zealand and Japan were the few countries left free from EVA over the past few dozen years. However, serological evidence of EVA was found in Standerdbreds in Australia and New Zealand in 1990 and EVA has been in Australia since 1975, while confirmed clinical EVA was not recognized [42, 68]. The majority of horses infected with equine arteritis virus (EAV) seem to have a mild or subclinical form all over the world [5, 6, 12, 33, 39, 42, 45, 49-51, 53, 60, 64, 70, 73, 98]. In contrast, fatal cases in foals and a neonatal foal have been reported in Poland [34, 35] and the USA . Furthermore, because EVA adversely affects racing [47, 50, 64] and results in a high rate of abortion in pregnant mares [9, 20, 34, 46], an outbreak of EVA in such horse populations may lead to significant economic loss. In recent years, there have been considerable number of international movements of horses for the purpose of trading, breeding and competition. Such movements could provide extensive spread of contagious diseases in horse populations which may be highly susceptible to exotic infectious diseases. Although only a few countries in the world including Japan have remained free from EVA, this article describes the clinical features and diagnosis of EVA, as well as the prevention and control of EVA, thus providing information which will be useful in minimizing suffering from a serious outbreak of EVA should it occur in horse populations that have been free of EVA.
Oligonucleotide probes specific for simple tandem repeat sequences produce individual specific DNA fingerprints in man and animal species tested so far. In the present study, a polynucleotide (TG)n was used to investigate DNA fingerprint variability in three breeds (Thoroughbred, Tokara horse and Noma horse) in order to clarify the relationships among Japanese native horses by using DNA fingerprinting (DFP). Estimates of the probabilities of finding identical fingerprints in two unrelated individuals of different breeds were in the range from 2.1×10-1 to 3.6×10-5.Similarities in DFP patterns between individuals were estimated by using the band sharing (BS) value. From the BS values, individuals within breeds tended to be more similar to each other with regard to DFP pattern than to individuals of other breeds. Furthermore, the genetic distance among the horse breeds was estimated as the mean number of nucleotide substitutions per nucleotide site. All individuals of three different ferent breeds were distributed into particular clusters and the Tokara horse was far from other breeds. DFP analysis can therefore be effectively used to assess the genetic relationship among breeds of horses.
The antibody response of foals to the antigens of virulent Rhodococcus equi was studied on two horse-breeding farms contaminated with R. equi using Western immunoblotting, and the results were compared with the antibody titers measured by ELISA. Virulent R. equi ATCC 33701 was used as an antigen for these immunoassays. Sera were collected five times from 19 foals on the two farms at regular intervals. ELISA titers o f these sera increased within 60 days after birth, and then gradually decreased to adult levels. Antibody response to the 15- to 17-kDa antigens was detected in accordance with the increase in ELISA titers in every foal. Some of the foals with clinical signs of respiratory tract infection showed a significant increase in ELISA titers. On these farms, virulent R. equi was isolated from their environmental soil. These results suggest that the foals studied were naturally exposed to virulent R. equi, and that humoral response to the 15- to 17-kDa antigens developed in accordance with age during the first 3 months of life
The present study was undertaken in effort to describe the relationships among each step length, stride length, stride frequency, and velocity during the start dash. Stride frequency reached its peak immediately after the start, while stride length required about 25-30 strides to reach its maximal level. Although substantial increase in velocity was attained by an increase in stride length, it appears that acceleration during the start dash is achieved by maximal increase in stride frequency. Mid step length reached a maximum level following several strides, however airborne step length required more time to reach its maximum. Therefore acceleration during the start dash is achieved by a maximal increase in mid step length since it is not possible to quickly increase airborne step length.
Heart rate, R-R intervals and the number of jaw movements were measured simultaneously for a 24-h period in an adult horse in a housed free-moving state. Feeding behavior was characterized by the number of jaw movements. Dropped beats could be monitored from a series of R-R intervals, and these dropped beats were regarded as second-degree A-V blocks . Thirty-eight dropped beats occurreduring a 24-h period. Second-degree A-V blocks frequently occurred in the night (p<0.001) and scarcely occurred in the active feeding periods (p<0.001). Moreover, the R-R interval periodically fluctuated at rest in the night. It was speculated that this periodical fluctuation in R-R interval is a respiratory sinus arrhythmia. This arrhythmia was not observed during feeding periods. A periodic violent fluctuation in the R-R intervals persisting for about 10 min was observed in the interval between feeding periods in the middle of the night, and this episode might occur during paradoxical sleep (REM sleep).