Nine three-day event horses were divided into two groups. In Group A (4 horses), prior to the start of training, horses were subjected to standardized exercise test (SET) A: after a warm-up of 5 min walking and 6 min trotting, horses were galloped at 400 m, 500 m, 600 m, and 700 m/min over 1000 m with 5 min walking in between. In Group B (5 horses), after four months of training, horses were subjected to SET B: after a warm up of 5 min walking and 20 min trotting, horses were galloped at 400 m, 500 m, and 600 m/min over 1000 m with 5 min walking in between. For the SET of Group A, six physiological indices (V₁₅₀, V₂₀₀, V_LA2, V_LA4, HR_LA2, HR_LA4) were determined. Among these, V_LA4 is an important index, being the exercise intensity needed to improve both aerobic and anaerobic capacities. At the conclusion of SET A, since blood lactate levels exceeded 4 mmol/l the final gallop at 700 m/min was eliminated. Two horses in Group B required a more intense exercise to realize blood lactate levels of 4 mmol/l. Increasing the exercises intensity of SET B can be accomplished by shortening the walking interval between galloping exercises, and this would decrease the risk of musculoskeletal injury.

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Plasma adrenaline (Ad), noradrenaline (NA), adrenocorticotropin (ACTH) and cortisol responses to exhaustive incremental treadmill exercise were investigated in seven Thoroughbreds. Blood lactate (LA), heart rate (HR) and oxygen uptake (VO₂) were measured and their correlations with plasma hormone levels were examined. Although the magnitude of plasma Ad, NA and ACTH response to the exercise was great, that of cortisol was very slight. Plasma Ad and NA levels reached peaks at exhaustion in all Thoroughbreds. On the other hand, plasma ACTH levels reached peaks at a different time in each Thoroughbred, followed by a 10-15 min delayed peak of plasma cortisol levels. The maximal levels of plasma Ad, NA, ACTH and cortisol were significantly 300, 150, 70 and 1.8 fold higher, respectively, than the pre-exercise levels. Plasma Ad, NA and ACTH during exercise were highly and significantly correlated to each other. The noticeable increase in plasma Ad levels during exercise was characteristic of Thoroughbreds. Plasma Ad, NA and ACTH responses during exercise were significantly correlated with treadmill velocity, blood LA, HR and VO₂ in an exponential manner. The threshold for blood LA was significantly lower than the threshold for Ad, NA and ACTH. In conclusion, the present data on plasma CA and ACTH responses to exercise suggest that the sympathoadrenal axis and the pituitary gland are highly activated by exercise in Thoroughbreds. In addition, it is suggested that plasma CA and ACTH levels as well as LA and HR may be useful indicators for estimating exercise stress and physical fitness in the Thoroughbred.

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A panel of overlapping peptides covering the ectodomain of the G_L protein of equine arteritis virus (EAV) was synthesized to identify the major epitope recognized by the EAV-seropositive horse sera by using enzyme-linked immunosorbent assay (ELISA). Three consecutive peptides, G15 (amino acid residues 75-90), G16 (79-94) and G17 (83-98), strongly reacted with 3 experimentally EAV-infected horse sera. G16 peptide was highly antigenic with all 8 EAV-infected horse sera tested. The ELISA absorbance values and the virus neutralization titers of antibodies in sera periodically collected from EAV-infected horses showed similar patterns. These results indicated that the major linear epitope of the EAV G_L protein which was recognized with EAV-infected horse sera was mapped to residues from 83 to 90.

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Intranasal infection with 10⁵ TCID₅₀/25 μl of the HH1 strain of EHV-1 in pregnant BALB/cA mice at 15 to 17 days of gestation resulted in not only clinical signs in dams such as suppression of body weight gain, ruffled fur, hunched posture and depression but also fetal growth retardation and death which were indicated by the degree of decrease in body weight at parturition, litter size and gross appearance of neonates, but the virus could not be demonstrated in any neonates tested.

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Effect of exercise on apparent energy digestibility of timothy and alfalfa hay were estimated in two-year-old horses. Intensity of the exercise was equal to 80% heart rate max (180 beats/min) for 5 min between warm-up and cool-down. Timothy and alfalfa hay intakes in the exercise and rest periods did not differ significantly. The apparent energy digestibility and digestibility energy (DE) of timothy hay in exercised horses were significantly lower than in rested horses but there were no significant differences between exercised and rested horses in the apparent energy digestibility or DE of alfalfa hay. These results suggested that exercise in this study decreased energy digestibility of timothy hay and it seemed that the effect of exercise on the energy digestibility of hay was altered by the composition of hay.

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