RESUMEN
Infections caused by nematodes of the subfamily Cyathostominae affect nearly 100% of pastured horses. Despite of an absence of pronounced symptoms, cyathostominosis can have very serious health consequences. The aim of this study was to monitor changes in total protein levels and concentrations of selected microelements and macroelements in the blood of horses before and after ivermectin treatment. In healthy horses infected by the studied parasites, total blood protein levels were below the physiological norm, but iron (Fe), magnesium (Mg), calcium (Ca) and phosphorus (P) concentrations were within normal limits. Ivermectin treatment reduced the number of excreted parasite eggs (FEC) by 100%, and dead parasites were observed in feces. Decreased iron (Fe) concentrations and an insignificant increase in total blood protein levels were reported. A progressive decline in iron levels was observed when parasite eggs reappeared in feces 60 days after treatment. Iron loss takes place as a result of bleeding from the large intestine when adult nematodes affected by the drug are removed from intestine and fourth-stage larvae leave parasitic nodules in the intestinal wall. A drop in iron levels could be an indirect indicator of the severity of cyathostominosis.