Investigation of blood iron metabolism in healthy adult horses and in horses with acute inflammatory disease

The transport of oxygen in the organism is the main task of iron in mammals and thus also in the horse. Functional iron, which is found in haemoglobin, myoglobin and iron-containing enzymes, among others, covers this task. Iron homoeostasis is maintained by depositing and storage of iron on specialised iron-binding-proteins. These iron-binding-proteins include transferrin for the transport of iron in the blood and ferritin and hemosiderin for the storage of iron in several tissues. Under certain influencing factors, such as physical exercise and oxidative stress, iron-rich diet or certain diseases, redistribution of iron between tissues and blood may occur. Hepatopathies, nephropathies and also neoplasia can influence such a redistribution, but mainly it is determined by an acute systemic inflammatory disease, which will be investigated in more detail in the current study. For this purpose, an adult horse population was classified as healthy or affected by an acute inflammation based on certain inclusion criteria, such as serum amyloid A (SAA) levels, white blood cell count, and other clinical signs, such as increased internal body temperature, which may indicate acute systemic inflammation. A blood sample was taken once from both healthy (n = 71) and sick horses (n = 65), from which haematology, clinical chemistry parameters, and iron metabolism parameters were subsequently determined. From the results of the blood sample examination, the suspected diagnosis of acute systemic inflammation of the sick horses manifested itself, because of the significant differences in the SAA concentration in the serum of the two groups. All healthy horses (median = 0.10 mu g/mL) showed SAA levels < 7 mu g/mL (*lab internal, reference value < 7 mu g/mL, LABOKLIN GMBH & CO.KG) and all sick horses showed SAA levels > 7 mu g/mL (median = 421 mu g/mL). Likewise, serum iron parameters, such as ferritin concentration, iron concentration, unsaturated iron binding capacity (UIBC), total iron binding capacity (TIBC), and iron saturation, showed highly significant differences between the healthy and the sick horses. In the sick horses serum iron concentration (median = 0.65 mg/L) and iron saturation (median = 18.51 %) were significantly lower than in healthy horses and the concentration of ferritin (median = 26.5 mu g/L), UIBC (median = 3.09 mg/mL) and TIBC (median = 3.71 mg/mL) higher than in healthy horses. Significant differences between healthy and sick horses were also seen in glucose, albumin, globulin, creatinine, copper, and some liver parameters. All median blood levels, except that of LDH were within the reference range for healthy horses. For the levels of iron parameters, there are currently no reference values for adult horses available, except for the serum iron content, which deviated from the reference range in the sick horses. Comparing the current data and the results of other studies, similar values are found for serum iron concentrations as well as for UIBC and TIBC. Such similarity cannot be seen in the ferritin contents, where differences in the concentrations in the healthy and in the sick horses were first shown here. The levels of iron saturation are very variable in the literature and reported as a wide range and must be adapted to the basic conditions of the experiment, the measurement methods, and the animals. The changes in iron metabolism parameters suggest a redistribution of iron in the organism during acute systemic inflammation and can possibly be used in conjunction with other acute phase proteins as markers of this condition.