The sire effect and the fixed effects of sex, training center, type of course, specific racetrack, horse age and track condition were evaluated regarding best racing times of thoroughbred horses. The records of best racing times at the Japan Racing Association were collected from the electronic racing book. The data set was edited so that each sire was required to have at least twenty progeny in the racing distances of 1200m and 1800m. The total numbers o f sires and progeny were 34 and 1486 for 1200m and 34 and 1520 for 1800m. First, the least-squares analysis of variance was carried out by using the linear model which included the sire effect and the six fixed effects. Second, heritabilities for best racing times were calculated, and additionally sire evaluations were carried out by using the sire model of the BLUP method. As a result of analysis of variance, almost all effects included in the linear model were significant for both racing distances. The sire, type of course, horse age and interaction between the type of course and track condition had a highly significant effect on best racing times. Estimates of heritability were 0.11 and 0.09 for 1200 m and 1800 m, respectively. Rankings of sires' breeding values based on progeny records were quite different for the two racing distances. The Spearman rank correlation coefficient for these rankings was 0.350 (P<0.05).
Among race horses raised and trained at Ritto Training Center of the Japan Racing Association, an epizootic of respiratory disease was observed from January to February in 1989. During the epizootic, a total of 155 out of approximately 2, 000 race horses developed pyrexia. Following the respiratory symptoms, 7 Thoroughbred horses showed various degree of nervous disordersuch as incoordination of the hind limbs to recumbency with urinary incontinence. Previous study briefly reported a result of virus isolation, in which 10 EHV-1 strains were isolated from febrile horses involved in this epizootic. In this study, clinical, serological, and molecular-biological researches were conducted to elucidate an epizootiological aspect of this occurrence of EHV-1 infection. Serologically, 90 (67.7%), including 7 samples from the horses manifested nervous disorders, out of 133 paired serum samples collected from febrile horses showed significant antibody response (four-fold or greater increase in the antibody titer) against EHV-1 by complement fixation and/or serum neutralization tests. Majority (more than 85%) of the infected horses as judged by serological tests were 3 years old. By restriction enzyme and Southern blot analyses o f DNAs extracted from 10 EHV-1 isolates, including an isolate from one of the 7 horses manifested nervous disorders, the Bam HI cleavage pattern corresponded to that of the electropherotype 1 P of EHV-1 and closely resembled each other. However, minor variations were detected in the electrophoretic mobilities of certain Bam HI fragments. These results confirmed that the epizootic of respiratory disease occurred among race horses at Ritto Training Center in 1989 was caused by EHV-1 infection, and strongly suggest that the nervous disorders observed among febrile horses involved in the epizootic were caused by the paralytic form of EHV-1 infection, which had never been recognized among horses in Japan. However, no distinct difference was detected between DNAs o f the isolate from a horse with paralysis and of the isolates from horses without paralysis in the Bam HI restriction profile.
An ambulatory data-logging system for recording heart rate and/or the R-R interval in horses was developed. This system consisted o f a pulse generator for detecting heart beats and a data memory apparatus. The pulse signal generated by the pulse generator was fed to the data memory apparatus, and the heart rate and/or R-R interval was measured. The heart rate o f a riding horse was recorded for over 24 h and the accuracy in determining heart beats was monitored with an ambulatory EGG recorder. False beat counts were 0.04% of total heart beats during the housed period and 1.6% during the grazing period in a paddock. It was thought that this system might become a useful tool to use in studying behavior and physiology based on the heart rate and/or R-R intervals in free-ranging horses.
A subepiglottic cyst, found in a young thoroughbred horse which showed respiratory noise during exercise, was resected by means o f a wire snare fed with high current while viewing under oral endoscopy. In comparison with the laryngotomy and pharyngotomy approaches reported elsewhere in the literature, the present method proved to be safer, inflicted less surgical stress, and required a shorter recovery period. The histopathological study did not clarify the tissue origin but the location o f the cyst suggested it to be derived from the thyroglossal duct.