Xylazine is the most commonly used equine tranquilizer but its effects on ovulation and periovulatory endocrinology have not been tested in the mare. In this study, mares received xylazine (0.5 mg/kg IV) or vehicle during synchronized follicular development. The diameter of the dominant ovarian follicle was monitored every twelve hours by ultrasonography and the time of ovulation was recorded. Serum concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH) and progesterone were measured by radioimmunoassay. Xylazine transiently but significantly increased concentrations of FSH. LH and progesterone profiles as well as follicular diameters and the timing of ovulation were similar following treatment with xylazine or vehicle. A single tranquilizing dose of xylazine is unlikely to alter ovulation in the mare.
We performed pathological analysis of the skeletal muscles obtained from a racehorse that showed astasia after halothane anesthesia. Light microscopic examination revealed that skeletal muscle fibers had undergone degenerative changes such as coagulation necrosis, segmental rarefaction, and granular degeneration. Electron microscopic examination revealed damage of sarcomeres. Fragmentation of the actin filaments without Z-discs degeneration was seen in some areas in which rarefaction was observed under a light microscope. Electron microscopic examination demonstrated degenerated muscle fibers, which are commonly observed during the process of skeletal muscle degeneration. However, we also observed marked degeneration of the actin filaments. This change differed from the myofibril degradation process, explained so far, suggesting the existence of a mechanism by which actin filaments are predominantly degraded.
Five ponies and two donkeys suspected of having nutritional secondary hyperparathyroidism (NSH) were put on an improved diet with a phosphorus:calcium ratio of 1:1.5. Changes in serum phosphorus, calcium, intact-PTH, and calcitonin concentrations were monitored for 1 year. High levels of phosphorus, intact-PTH, and calcitonin in the blood caused by NSH were significantly reduced two months after the improved diet was started, although the calcium level in the blood hardly changed (P<0.05). Therefore a diet with well balanced minerals can help ponies and donkeys recover from NSH.