To find a new parameter indicating muscle fitness in Thoroughbred horses, we examined time-dependent recovery of glycogen content and sarcoplasmic reticulum (SR) Ca²⁺-ATPase activity of skeletal muscle after intensive treadmill running. Two repeated 50-sec running sessions (13 m/sec) were performed on a flat treadmill (approximately 90%VO₂max). Muscle samples of the middle gluteal muscle were taken before exercise (pre) and 1 min, 20 min, 60 min, and 24 hr after exercise. Muscle fiber type composition was determined in the pre muscle samples by immunohistochemical staining with monoclonal antibody to myosin heavy chain. SR Ca²⁺-ATPase activity of the muscle and glycogen content of each muscle fiber type were determined with biochemical analysis and quantitative histochemical staining, respectively. As compared to the pre value, the glycogen content of each muscle fiber type was reduced by 15-27% at 1 min, 20 min, and 60 min after the exercise and recovered to the pre value at 24 hr after exercise test. These results indicate that 24 hr is enough time to recover glycogen content after short-term intensive exercise. The mean value of the SR Ca²⁺-ATPase activity showed a slight decrease (not significant) immediately after exercise, and complete recovery at 60 min after exercise. There were no significant relationship between the changes in glycogen content of each muscle fiber type and SR Ca²⁺-ATPase. Although further studies are needed, SR Ca²⁺-ATPase is not a useful parameter to detect muscle fitness, at least in Thoroughbred horses.

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A broodmare showed mild signs of abdominal discomfort and anemia after normal delivery. Ultrasonographic examination revealed a massive hematoma within the broad ligament adjacent to the uterine horn. Internal bleeding into the peritoneal cavity (hemoabdomen) was not seen. Following treatment, the clinical signs improved. Hemorrhage caused by rupture of the arteries within the broad ligament of the uterus may be a cause of hematoma. Prepartum and postpartum rupture of the arteries supplying the reproductive organs in the mare, which is not uncommon, can be fatal if severe hemoabdomen occurs. In the present case, the hematoma was considered to be tightly encapsulated between two serosal membrane layers of the broad ligament, and the membranes had remained intact. Thus, the serosal membranes did not split open, and massive bleeding into the peritoneal cavity did not occur. For this reason, the present broodmare avoided potentially fatal hemorrhagic shock.

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