In an attempt to estimate the number of gene-loci controlling the racing performance and the effect of the genes concerned, an analysis was carried out on the racing results of some Thoroughbreds. These horses were born by foreign sires during a period from 1970 to 1978 and ran on good conditions at the age of three years for 1200m, 1400m, 1600m, and 1800m on the turf or dirt-course. If it is allowed to take a portion where the probability of the chi-square distribution is high, it will be presumed that the number of gene-loci controlling the racing performance may be in the neighborhood of N=7-10 (average, 7.9) and that the effect of the genes may be α=0.8-1.4s (average, 1.02s). Another method of estimation of the number of genetic factors was worked out by Furusho. Then the number of gene-loci controlling the racing performance and the effect of the genes concerned were estimated to be N=9-24 (average, 14.2) and α=0.3-0.8s (average, 0.52s), respectively. Taking these two N-values and two α-values into consideration, it was presumed that the number of gene-loci controlling the racing performance and the effect of the genes concerned might be in the neighborhood of N=7-24 (average, 11.5) and α=0.3-1.4s (average, 0.73s), respectively.

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It is an important problem to study diurnal changes in measurements of body parts in the Thoroughbred when a large number of horses are measured in the course of a day. In this study, 24 body parts were measured in 43 Thoroughbreds at three different times, the day before training, immediately after training, and after grazing. As a result, there were significant chronological differences in the measurements of few parts by the analysis of variance, but such difference was significant at 5% levels in thickness of the breast. The difference in thickness of the breast, however, was considered to be within the range of measuring error. It seems to be the best way to measure Thoroughbreds at the same time on the same day, but no statistical errors will be produced, if all horses are measured on the same day.

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In order to estimate the change of a number of body parts in accompany with the growth, 24 parts of the body were measured chronologically in 259 male and 171 female Thoroughbreds born over a period from 1979 to 1982. The measurement was undertaken over a period from 300 to 1320 days of age. The following results were obtained. (1) In the early period, the height of the croup was greater than the body length. It became the same as the body length until 720 days of age, and was surpassed by the latter at 1200 days of age. (2) From 300 to 1320 days of age, the growth rate of body length was higher than that of body height at the withers, at the back, or at the croup. In this study, the growth rate of length of the breast was 65-75% of that of body length. (3) The growth in thickness of the point of the hip was more remarkable in females than in males. The growth in circumference of the forearm, cannon, gaskin and hind cannon, however, was more distinct in males than in females. (4) The highest growth rate was shown by the circumference of the breast of all the 24 parts of the body.

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In order to clarify the histological reactions to pin-firing, this procedure was applied experimentally to four horses, which were subjected to a histopathological investigation as focus with the skin. The course of inflammation in these horses was divided into three stages, (1) The next day of application (exudation stage), (2) 3 to 11 days after application (cell migration stage), and (3) 14 to 21 days after application (repairing stage). In stages 2 and 3, the eosinophil and mastcell infiltration in the vicinity of arterioles and capillaries within the granulation tissue deserved particular attention since it seemed to indicate a local immunological reaction. Moreover, the swelling degeneration and the loss of axons in small nerve bundles were assumed to indicate that the function of pin-firing might consist in blocking nerves.

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A total of 282 horses 3 days to 25 months old on 99 farms in the Hidaka district, Hokkaido, were investigated. The clinical manifestations of epiphysitis in the metaphysis and epiphysis included the enlargement of the epiphyseal-metaphyseal region, and heat and pain in the region of swelling. Affected were the distal epiphysis of the third metacarpal and metatarsal bones and the proximal epiphysis of the first phalanx in horses 3 to 5 months old, the distal epiphysis of the tibia in horses 6 to 8 months old, and the distal epiphysis of the radius in horses 8 to 12 months old. Radiographic changes were associated with flaring and lipping of the metaphysis and epiphysis adjacent to the epiphyseal plate, and sclerosis in the epiphysis or metaphysis. They included thickening and crushing of the epiphyseal plate, radiolucency or radiodensity, disorderly trabeculae, and linear radiolucency which agreed with the direction of trabeculae in the metaphysis and epiphysis. Affected horses seemed to be normal at first sight for 7 or 8 months after the onset of disease, but they had several sequelae. Epiphysitis was closely related with the linear radiolucency of the proximal sesamoid bone, radiolucent cyst-like lesions, ataxia, enlargement of the hock, and contraction of tendons. The rate of occurrence of epiphysitis was 27% on 10 farms in the Hidaka district.

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Seroepizootiological studies were conducted on rearing horses on the Hidaka Rearing Farm, Japan Racing Association, over a period from 1980 to 1983. Antibodies against equine herpesvirus type 1 (HH-1 subtype), Getah virus (MI-110 strain), equine adenovirus (T-1 strain), and rotavirus (Lincoln strain of Nebraska diarrhea virus) were examined by the complement fixation test. Antibody against equine rhinovirus type 1 (NM-11 strain) was demonstrated by the virus neutralization test. Equine rhinovirus was considered to have spread most widely, as most of the horses examined showed a significant increase in titer of antibody in the winter. Equine adenovirus also presented a high positive rate at admission to this farm in 1981 and 1982. The rate of infection after admission differed from one year to another, ranging from 4 to 20%. Against rotavirus, 14 to 40% of horses had antibody at admission. And only 1 or 2 horses were infected every year. With equine herpesvirus type 1 the antibody positive rate at admission and infection rate differed among every year. In horses admitted in 1980, the positive rate at admission was 5% and the infection rate about 50% over a period from June to July, 1981. In horses admitted in 1981, both rates were very low. In horses admitted in 1982, the antibody positive rate was 47% at admission, but none were infected during the rearing period. No outbreak of Getah virus infection was observed during these studies, except that several horses introduced from Aomori Prefecture had antibody at admission.

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Antigenic relationships among equine and other animal rotaviruses and human rotavirus, and physicochemical properties of equine rotavirus were examined. In the cross complement fixation test, the BI and HI-23 strains of equine rotavirus cross-reacted markedly with the Lincoln strain of calf rotavirus, the S-80 strain of porcine rotavirus, the SA-11 strain of simian rotavirus, and the Wa strain of human rotavirus. It was not possible to distinguish one strain of equine rotavirus from the other by the complement fixation test. In the cross neutralization test, the two strains of equine rotavirus cross-reacted distinctly with the SA-11 strain of simian rotavirus, although their titer to homologous virus was 4 to 64 times as high as that to heterogous virus. On the other hand, the two strains of equine rotavirus did not cross-react with the Lincoln strain of calf rotavirus, the S-80 strain of porcine rotavirus or the Wa strain of human rotavirus. Replication of the BI strain of equine rotavirus was not inhibited by 5-iodo-2′-deoxyuridine, indicating that the virus was RNA virus. The infectivity of this strain was resistant to chloroform, ether and sodium deoxycholate, and stable at pH 3. It was relatively heat-stable and sensitivity to 1mol/l MgCl₂ at 50°C. From these results, it was revealed that the BI and HI-23 strains of equine rotavirus belonged serologically to the genus Rotavirus and were closely allied to the SA-11 strain of simian rotavirus as serotype. Moreover, it was confirmed that the BI strain possessed the same physicochemical properties as the genus Rotavirus.

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The ciliate fauna in feces was surveyed in 146 light horses (25 yearlings, 60 racehorses, 45 bloodmares, and 16 riding horses). The results obtained are as follows. (1) It was possible to identify 7 classes of ciliate protozoa, including 53 species belonging to 23 genera in light horses, 49 species to 23 genera in yearlings, 49 species to 22 genera in racehorse, 50 species to 22 genera in bloodmares and 45 species to 20 genera in riding horses. Of all the species, three had never been recorded before in Japan. (2) The average density of ciliates was 4.32×10⁴/ml in yearlings, 9.03×10⁴/ml in racehorses, 3.14×10⁴/ml in bloodmares, and 2.89×10⁴/ml in riding horses. So it was significantly higher in the racehorses than in any other horses. (3) The averagenumber of ciliate species harbored was 18.4 in yearlings, 21.0 in racehorses, 16.9 in bloodmares, and 16.6 in riding horses. It was significantly higher in the racehorses than in any other horses. (4) In the ciliate fauna in the feces of each group of horses, the incidence of each genus or species and the density of ciliates correlated significantly to each other. When ciliates were present at a high density, they tended to be distributed extensively.

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In racehorses, changes in glucose metabolism with training were observed by the glucose tolerance test. Four female Thoroughbreds were used in the present investigation. All of them had recorded more than one win during their racelife. The clearance rate of exogenous glucose from plasma was much slower in the horse than in any other monogastric animal. A delay in immunoreactive insulin (IRI) secretion, which was the same change as mentioned in the previous paper, was observed in the horse in a complete resting condition 4 months after they left the racecourse (always kept in stable during the period). In these horses, 6 weeks after the training, the IRI secretion was stimulated and the clearance rate became more than three times as high as that before the training (as high as, or higher than that in any other monogastric animal). From these results and the insulinic index determined by calculation, it was clear that glucose metabolism in the racehorse was influenced largely by exercise, and that a main reason for the change was not an increase in IRI sensitivity, but a much and rapid secretion of IRI from the pancreas.

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The standard values of electrocardiographic parameters, as changing with growth, were determined in Thoroughbred horses and Shetland ponies. The properties of electrocardiograms were compared among the two breeds and Holstein cows. Those of these cows in the course of growth had previously been published. Electrocardiograms in the A-B lead (apexbase bipolar lead) and the standard limb leads were recorded over a period from 1 week to 12 months after birth. The RR, PQ and QT intervals, and the P and QRS durations prolonged distinctly with growth. The deflections of the P wave were generally bifid. Their amplitudes were about 0.2mV for 12 months after birth. The deflections of the QRS complex were classified into rS or QS types in all the cases. In the ponies, the amplitudes of the R spike scarcely appeared after 2 months of age, and that of the S spike decreased with the advance in growth. In the Thoroughbreds, those of the R and S spikes were always stable, regardless of age. The PQ interval and the P wave duration were longer and the QT interval was shorter in the Thoroughbreds than in the ponies or cows. The deflection of the T wave showed characteristic changes in the Thoroughbreds and ponies with the advance in growth. It showed a negative or a negative predominant pattern at a few days of age, a positive predominant one for the following 30 days, and again a negative or negative predominant one after 2 months of age. In the cows, it was basically different. The general direction of the QRS vector on the horizontal plane hardly changed in the Thoroughbreds and ponies until 12 months of age, while it changed in the cows with the advance in age.

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Creatine kinase (CK) and lactate dehydrogenase (LDH) isoenzymes were determined at different time intervals in sera from racehorses with skeletal and cardiac muscle damage. In the case of the tying-up syndrome, the elevated activities of CK-MM₁ and LDH₅ bands were found according to the degree of clinical conditions. Two types of serum isoenzyme profile were seen in 26 cases of the serious group. In one type, the activities of MM₁ and LDH₅ bands increased considerably, and returned to the normal value within 7 days. Of the 26 cases, 21 (80%) were classified into this type and prognosis was favorable in them. In the other type, the activities of LDH₁ and CK-MB bands were elevated in addition to the profiles mentioned above. In this type, the complication of cardiac muscle damage was considered. The recovery of these elevated profiles was slow, requiring a few weeks to take place, with relapse or muscle pain. Prognosis was generally adverse in this type. The degree of damage in skeletal and cardiac muscles was clarified precisely by the analysis of CK and LDH isoenzymes. These analyses at different time intervals were very useful for clinical application to grasp variation in clinical conditions, make prognosis roughly, establish a proper therapy, determine the efficiency of therapy, and fix the time of resumption of training. Also, the attack of relapse or chronic muscle pain in the case of the tying-up syndrome with cardiac muscle damage would be preventable by the application of CK and LDH isoenzyme profiles.

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Histopathological studying on the lung in 10 aborted equine fetuses revealed the presence of eosinophilic substances in the pulmonary tissues, without exception. These substances were derived from the amniotic fluid and classified into four types according to morphology and stainability. They were distributed throughout the lobes, especially in the bronchioles and alveoli.

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A total of 40 viral isolates were recovered from the oral cavity in 28.4% of 141 clinically healthy horses of 5 groups. By the cross serum neutralization test, they were divided into 3 serotypes which were closely related with equine rhinovirus types 2 and 3, and strain 4442 of acid-stable equine picornavirus, respectively. Equine rhinovirus type 2 was recovered from rather young horses, and strain 4442 from both young and aged ones. Only one isolate which was identical with equine rhinovirus type 3 was isolated from a weanling. A follow-up study on virus isolation and serum neutralizing antibody detection indicated that virus titers ranging from 10^0.75 to 10^2.75 TCID₅₀/0.1ml were detectable from the saliva of horses showing little changes in serum neutralizing antibody titer. Therefore, it is probable that equine picornavirus may normally inhabit in the oral cavity and the infection of the virus may be widespread among horses free from any clinical disease.

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The agar gel immunodiffusion (AGID) test was used for the diagnostic and epizootiological studies of equine herpesvirus type 1 (EHV-1). As a result, it was evident that this test was useful for detection and titration of precipitating antibody against EHV-1. The antigen was prepared from concentrated EHV-1 by treatment with 1% Nonidet P-40 and sodium deoxycholate. It was specific only to EHV-1 and reacted commonly with some subtypes of EHV-l, such as HH-1, Kentucky-D, TH-20, and H-45. Most of the horses experimentally or naturally infected with EHV-1 demonstrated an increase in antibody from - or + in the acute phase to +++ or ++++ in the convalescent stage. When antibody was +, ++, +++, and ++++, its titers were 1 to 2, 4 to 8, 16 to 32, and 64 units or over, respectively.

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A survey was performed on antibody against Haemophilus equigenitalis in 4 312 mare sera collected in Japan over a period from 1975 to 1980 by using the complement fixation (CF) test with a simple washing culture of the organism as an antigen. Every year since 1978 CF antibody was detected from broodmares in Hokkaido, the northern part of Japan, where contagious equine metritis (CEM) was first diagnosed in 1980. It was also detected from 3 of 454 serum samples collected before covering in 1978. It was likely that CEM might have been introduced into Japan prior to 1978. CF antibody was detected from 20.9% of sera randomly collected from broodmares in the breeding region within 2 months after covering in 1980, but not from any racehorses or fillies during a period from 1975 to 1980. It was assumed that the organism might be widespread among broodmares in the breeding region, but not among racehorses or rearing horses.

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A bacteriological study was carried out to evaluate media and culture-conditions for isolation, growth and storage of Haemophilus equigenitalis. Chocolate agar plates made from eugon, modified Thayer-Martin and thiol agar media showed a better growth of bacteria than those made from any other medium and could be applied to primary isolation. The best growth of bacteria was observed on any agar media in an atmosphere containing 10% CO₂ and 75% N₂. Of 8 kinds of liquid or semisolid media, thiol broth and cystine trypticase showed an excellent growth of bacteria and a bacterial count ranging from 10⁵ to 10⁸ cells/0.1ml by 4 days of incubation. The survival of H. equigenitalis in liquid or semisolid media depend on medium and temperature. H. equigenitalis survived in all the media at -70 and -20°C for 3 years. When stored at 4 and 37°C, the bacteria survived in eugon, heart infusion, cooked meat, Brucella, and thiol broth for at least 8 weeks.

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A pathological study was carried out to comprehend the clinical findings of contagious equine metritis (CEM). Three mares, each of which was infected intrauterinely with 10², 10⁶ and 10¹⁰ cells, respectively, of Haemophilus equigenitalis, were necropsied at postinoculation day (PID) 9. In order to observe the development of lesions, additional 2 mares infected with 10¹⁰ cells of bacteria were necropsied at PID 3 and 6, respectively. As a result, the more organisms were inoculated, the more prominent clinical and pathological findings were obtained. In horses infected with 10¹⁰ cells of bacteria, these findings developed acutely at the peak on PID 6. All the 5 experimental mares manifested endometritis, cervicitis and vaginitis. Histopathologically, common findings were edema of the mucous membrane, migration of neutrophils into the lumen of the genital tract and infiltration of mononuclear cells in the lamina propria. Destructive changes of the endometrial epithelium and the uterine gland were observed only in a mare infected with 10¹⁰ cells of bacteria and necropsied at PID 9. H. equigenitalis with a large capsule multiplied on the luminal epithelium, but was never found to invade the epithelium. It seemed that the site of bacterial multiplication might be associated closely to the formation of pathological changes of CEM.

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Contagious equine metritis broke out for the first time in Japan in a breeding district of racehorses during the breeding season of 1980. Investigation was made for 2 weeks to detect 208 mares and 9 stallions from which Haemophilus equigenitalis was isolated. It was continued after the breeding season and revealed that a total of 297 mares and 13 stallions had been involved in the outbreak. The clinical characteristics of the disease in mares were essentially the same as reported previously in other countries. All the infected stallions were free from clinical signs and allowed to resume mating after treatment for a short time. Many mares responded to treatment with antibiotics and antiseptics, for example, penicillin, chloramphenicol and chlorhexidine. Of 297 infected mares, 152 conceived and 131 gave birth to full-term normal foals. The foaling rate was 86.1%, which was a little less than 93%, the average of this rate for the breeding district involved over the past 4 years.

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Viral agents were isolated from nasal swabs of 7 of 10 foals with pneumonitis and febricula. They were identified as equine herpesvirus type 2 (EHV-2) by comparison of antigenicity in the agar gel immunodiffusion test. However, little increase was confirmed in antibody titer against EHV-2 in only 2 foals. The reason for it should be that the foals had limited ability to produce antibody due to young age.

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Morphogenesis of equine rotavirus strain BI in MA-104 cells was examined. Numerous virus particles were detected within the cisternae of endoplasmic reticulum in the cytoplasm of infected cells. Three types of virus particles were found: core particles 30-40nm in diameter, single-shelled particles 55-60nm in diameter, and double-shelled particles 70-80nm in diameter. The outer layer of the double-shelled particle was formed by budding from the membrane of endoplasmic reticulum. Besides, tubular and honeycomb-like structures were observed in the cytoplasm of the infected cells.

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