EN
Fiber osteodystrophy (nutritional secondary hyperthyroidism) is an uncommon and poorly investigated disease of horses, connected with diet mistakes and secondary hormonal disturbances. The aim of this study was to asses selected biochemical parameters before and after the treatment of advanced forms of this illness. Horses from the control (healthy) and experimental groups were at the same age and originated from the same area. The affected horses were fed with fodder rich in phosphorus (oats). The horses of the control group were fed with corn mix, carrots, and sugar beets, and had free access to a saline lick. The clinical signs were big head symptoms, painfulness of cranial bones (especially the jaw bone), breathing problems, and joint pain in the extremities. P concentration in blood was statistically significantly lower, Ca and Mg concentrations were within the lowest physiological norms, and there was a significant increase in AST, AP and GGTP activity. After treatment, P concentration in blood increased statistically significantly, and hepatic indicators were slightly improved. The clinical symptoms remained unchanged.