The study group consisted of ten foals, 3-6 months old, 6 male and 4 female, KWPN breed, with developmental orthopedic disease (DOD). The control group consisted of eight healthy foals. On clinical examination, lameness, swelling of joints, and pain were observed in all foals. Clinical, radiographic, and pathological findings in ten foals indicated DOD. Serum Cu concentrations in foals with DOD were significantly lower than in the control group (0.094 +/- 0.011 mg/kg vs, 0.932 +/- 0.068 mg/kg, respectively; P<0.05). Serum Zn levels (1.828 +/- 0.180 mg/kg vs. 0.9257 +/- 0.052 mg/kg, respectively, P>0.05), serum Ca levels (187.836 +/- 7.921 mu g/dL vs. 150.912 +/- 5.271 mu g/dL, respectively, P>0.05), and serum P levels (247.339 +/- 10.729 mu g/dL vs. 190.470 +/- 5.775 mu g/dL, respectively, P>0.05) were observed both in foals with DOD and in healthy foals. There were no statistically significant differences between the DOD group and the control group with respect to serum levels of Ca, P and Zn. We concluded that DOD is associated with reduced serum levels of Cu in foals. Copper is an important trace element for growing foals.