Knowledge about changes in the osmotic fragility of erythrocytes during exercise in athletic horses which is introduced in this review can be summarized as follows; 1) Changes in the osmotic fragility of equine erythrocytes during exercise are an important indicator of intravascular haemolysis. 2) The sensitivity of the regulatory volume is decreased by a K-Cl cotransporter, lactate and/or pH susceptibility, and the osmotic fragility of erythroid membrane due to exercise stress increases with the repeated accumulation of red cells in the spleen. 3) The increase in blood flow and the release of erythrocytes from the spleen into the circulation have little effect on the changes in the osmotic fragility of erythrocytes during exercise. 4) Increases in blood pH and temperature caused by aerobic exercises cause osmotic resistance in erythrocytes. 5) The decrease in pH and increase in blood lactate and peroxide caused by anaerobic exercises promotes the osmotic fragility of erythrocytes. 6) The osmotic fragility of erythrocytes could be detected by the modification, degeneration, decomposition and oxidation-reduction in cell membrane lipids and proteins, and cell volume regulation, changes which follow pH and temperature changes during exercise. 7) The K-Cl cotransporter which controls the intracellular ionic homeostasis and regulatory volume decrease has a functional interrelation with the fragility of erythrocytes. The osmotic fragility of erythrocytes in athletic horses is therefore an indicator of the effects of training and/or athletic performance and stress.

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We investigated effects of xylazine and medetomidine on contractive motility in different regions of the intestine in conscious horses, to provide some insight into elucidation of the regional difference in the painrelieving effect of α₂-adrenergic agonists. We used 6 healthy adult male thoroughbread horses. Horses were intravenously given one of two calmatine-anodines, xylazine (1.0 mg/kg) and medetomidine (0.0075 mg/kg). The jejunum, cecum, and right ventral colon were examined for contractive motility. Both xylazine and medetomidine inhibited contractive motility for relatively similar durations, the effect of medetomidine was more potent than that of xylazine. After the horses were treated with both drugs, the contractive motility of the cecum and colon was inhibited for a longer duration and the inhibition was more intense than the corresponding duration and intensity of inhibition of the jejunum. These results suggest that the cecum and colon of the horse is more sensitive than the jejunum to α₂-adrenergic agonists.

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To study the differences between Hokkaido native horses and light half-bred horses on woodland pasture from the nutritional and behavioral viewpoint, feed intake, grazing time, moving distance, daily staying area and distance to the nearest neighbor were measured. Voluntary dry matter intake per body weight and metabolic body weight of Hokkaido native horses were higher than those of light half-bred horses (2.0 vs 1.8%, 88 vs 86 gDM/kgMBW), and the body weight loss of Hokkaido native horses during the experimental period was smaller than that of light half-bred horses. Grazing time, total moving distance, especially the moving distance with grazing were longer for Hokkaido native horses than for light half-bred horses. The distributions of distance between the nearest neighbor horses of the same breed for both breeds were similar. The distance from the one breed to the nearest neighbor of the other breed was greater than that within the same breed (P<0.01). The mean distance from the first position of a horse to its position at 1 hr intervals for Hokkaido native horses was 162 m, which was greater than 65 m for light half-bred horses. The daily staying area of Hokkaido native horses throughout the period of observation was larger than that of light half-bred horses. The differences between the two breeds in voluntary intake and behavior seemed to be large, but these differences were not significant.

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Melanoma, a kind of carcinoma cutaneum, occurs at high frequency in aged gray horses. For the basic study of horse melanoma occurrence, the establishment of melanoma culture cell lines derived from three aged gray horses was attempted. Three types of enzymes, collagenase, hyaluronidase and pronase, were used for the separation of melanoma cells in the primary culture. Those enzyme treatments were highly efficient for the resolution of connective tissue. The culture medium was Iscove's modified Dulbecco's medium (IMDM) + 10% fetal calf serum (FCS; Toyobo) and the culture condition was 37°C temperature, 100% humidity, 5% CO₂ and 95% air. After cloning a separated cell, three cell lines term culture were established for long term culture. These culture cell lines were named EMT-1, EMT-2 and EMT-3, respectively. These cell lines had high growth ability and the colony of the cell line was formed by a low density culture. The form of each culture cell, the cell surface and the distribution of the cytoskelton completely agreed with the characteristics observed in cancer cells. The numbers of chromosomes in these culture cell lines showed wide distribution mainly on 2n=64, and the hereditary characteristics were different from normal cell lines. Lactate dehydrogenase (LDH), nucleoside phoshorylase (NP) and glucose-6-phosphate dehydrogenase (G6PD) isozyme patterns of these culture cell lines were compared by starch gel electrophoresis, but there was no difference from the original cells. As a result of the above, it is considered that there was no contamination between the culture cell lines and the culture cells that came from the horse melanoma which showed signs of special hereditary variation.

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