Optical density (OD450) of an indirect enzyme-linked immunosorbent assay (ELISA) for detection of antibody to equine herpesvirus type 1 (EHV-1) was compared with agar gel immunodiffusion test (AGID) which is practically used for titration of antibody to the virus in clinics, complement fixation (CF) and neutralizing antibody titers. The correlation coefficient among them was 0.83, 0.67 and 0.44, respectively. The OD₄₅₀ of ELISA was strongly correlated with antibody levels which were expressed by AGID as follows. The mean OD₄₅₀ value ± standard deviation of -, +, ++ and +++ samples in the AGID, was 0.27 ± 0.12, 0.43 ± 0.22, 1.10 ± 0.34 and 1.38 ± 0.26, respectively. Change of OD₄₅₀ in a horse experimentally inoculated with EHV-1 was the same with that of precipitating antibody titrated with AGID and CF antibody. From these results, it was suggested that ELISA can be practically used in place of AGID for control of EHV-1 infection through titration of antibody to the virus in the field. The antigen for ELISA and AGID was suggested to be as VP 19, an inner component of the virus, because the major peptide of the antigen of both tests was estimated to have a molecular weight of 61, 000 daltons by polyacrylamide gel electrophoresis.

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An easily performed test that can provide accurate, rapidly available results for quantitation of horse IgG has been developed using nephelometry. This test is expected to be used for diagnosis of such immunological diseases as failure of passive transfer of colostral immunoglobulin from mares, which is the most common immunodeficiency disorder in foals. Correlation coefficient and p value among results for single radial immunodiffusion test and the nephelometry in 58 half-bred horses were 0.850 and < 0.0005. The test was applied to quantitation of serum IgG from 100 race horses. The mean value was 1, 603 mg/dl, with a standard deviation of 294.8 mg/dl, a minimum value of 1, 004 mg/dl, and a maximum value of 2, 391 mg/dl. The test was also utilized to clinical practice in a farm. A relationship between IgG quantity at seven days after birth and the period from birth to the first day of therapy for clinical illness was observed for 16 foals of a farm until 180 days after birth. The IgG quantities at seven days after birth was 140 to 1, 700 mg/dl, and 12 foals were treated for common cold, bronchitis or pneumonitis within 135 days after birth. This result suggested that foals have the same possibility for clinical illness, regardless of their IgG quantities at seven days after birth. However, treated foals with lower IgG quantities tended to show clinical illness earlier after birth.

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Monoclonal antibodies (mAbs) to red cell antigens of horse were produced by the standard method. Seventeen kinds of mAb (NHA-1, NHA-19, I-1C12, I-3E3, NHA-2, NHA-3, I-1E3, I-1A3, NAH-20, NAH-26, NAH-18, TA-1, NH-23, YA-1, I-3F10, 5C8 and NH-15) to horse blood group antigens were established, and their specificities were determined by the comparison test of the International Society for Animal Genetics. Out of these mAbs, both NHA-3 (anti-A₂-dose) and I-1A3 (anti-Ax-dose) recognized antigens belonging to the A system. The titer of the NHA-3 varied with the presence or absence of Aa and Ab antigens, whereas that of the I-1A3 varied with the presence or absence of Aa and Ac antigens. The NH-15 (anti-Px-dose) recognized antigens of the P system, and its titer varied with the presence or absence of the Pc antigen of this system. The quantitative antigen, recognized by the NAH-18 (anti-Ca-dose) belonging to the C system, was found to occur in larger quantities on the red blood cells in heavy breeds than on those in light breeds. The present study showed that these mAbs prepared to horse blood group antigens may be useful for more detailed analysis of antigenic subtype relationships and quantitative antigens.

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We investigated the effect of training intensity difference on cardiorespiratory parameters in twelve 2 year-old Thoroughbred horses during 8 weeks of training (5 days/week). Six horses were trained according to conventional training method including cantering (Canter group), while other 6 horses were exercised only by walking and trotting throughout the same period (Trot group). Each horse performed an incremental exercise test on a treadmill before (Pre-test) and after (Post-test) the training period. In the Pre-test, there were no significant differences between the Canter group and the Trot group regarding Vo_2max (154.7 ± 7.8 ml/kg/min in the Canter group, 147.2 ± 7.5 ml/kg/min in the Trot group). After the training period, Vo_2max was significantly higher in the Canter group (165.0 ± 11.6 ml/kg/min) compared to the Trot Group (150.3 ± 14.7 ml/kg/min). There were no differences in either group regarding the relationship between HR and speed, or La and speed in the Pre-test. During the Post-test, changes in HR in relation to the speed tended to be lower in Canter group, and La was also slightly lower in this group. Peak values of PCV increased significantly in both groups after the training, however, there were no differences between the groups. These results suggest that even low intensity training such as trotting can maintain Vo_2max. This indicates that higher intensity training involving cantering is not necessarily required merely to maintain cardiorespiratory function of 2 year-old Thoroughbred in early stage of training. However the findings also indicates that higher intensity training is required to substantially improve cardiorespiratory function in 2 year-old Thoroughbred horses.

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Circadian variations in catecholamines (CA) in the Thoroughbred horse were investigated by determining plasma adrenaline (Ad) and noradrenaline (NA) concentrations every 2 hr by high-performance liquid chromatography with an electrochemical detector (HPLC-ED). The HPLC-ED method in the present study was sufficient for determining plasma CA concentrations. The elution of CA from alumina with a mixture of acetic acid and methanol (1:50, v/v) gave a good recovery. The detection limit for both Ad and NA was 10 pg/ml. A significant variation during the 24 hr was observed for plasma NA concentrations (P<0.01), but not for plasma Ad concentrations. From 14:00 hr to 18:00 hr, plasma NA concentrations were significantly higher than those observed from 02:00 hr to 04:00 hr (P<0.01). As a result of the cosinor analysis for individuals, a circadian rhythm of plasma concentrations of Ad and NA was demonstrated (mean ± SE, 26.3 ± 4.6 pg/ml and 66.3 ± 3.8 pg/ml; rhythm amplitude, 9.4 ± 1.4 pg/ml and 12.7 ± 1.2 pg/ml; time of trough, 02:34 hr: min ± 9.7 min and 02:54 hr: min ± 33 min for Ad and NA, respectively). The 6 hr continuous tie-stall-type restraint decreased plasma concentrations of Ad and NA and delayed their peaks by 4 hr and 2 hr, respectively. There was a significant correlation (n=48, r=0.562, P<0.001) between the circadian variations in plasma Ad and NA. In conclusion, it was found that circadian variations in plasma CA in the Thoroughbred horse were similar to those in humans. In addition, the present study suggests that the sustained stress may influence circadian variations in plasma CA.

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