Abstract: Objective  To detect the immune status and antioxidant system indexes of cows infected with Cryptosporidium.  Methods  Fecal samples of 325 dairy cows were collected at a farm in Anhui and examined by floating saturated solution. 7 positive cows and 7 negative cows from the farm were selected as infection group and non-infection group， respectively. Blood samples were taken from cow′s jugular vein before feeding in the morning. 19 indexes of total protein (TP)， albumin (ALB)， IgG， IgM， IgA， phagocytic rate of white blood cells， T lymphocyte transformation rate， IL-2， superoxide dismutase (SOD)， glutathione peroxidase (GSH-Px)， malondialdehyde (MDA)， NO， alanine aminotransferase (ALT)， aspartate aminotransferase (AST)， alkaline phosphatase (ALP)， glucose (GLU)， triglyceride (TG)， Cl^－， and Ca²⁺ were tested， respectively.  Results  The infection rate of 325 cows was 31.7%（103/325）. The Cryptosporidium was identified as C. andersoni according to the morphology and size of oocysts. Compared with the non-infection group， there was no significant difference in the concentration of TP， ALB， IgM， IgA， GSH-Px， ALT， AST， ALP and Cl^－ （P>0.05）. The concentration of MDA and NO in the infection group increased by 59.9% and 28.1% （P<0.05 or 0.01）， and that of IgG， SOD， GLU， TG， Ca²⁺， IL-2 and the activities of T lymphocyte transformation rate， phagocytic rate of white blood cells decreased by 32.9%， 11.1%， 18.6%， 78.9%， 14.5%， 7.0%， 22.0%， and 20.2%, respectively （P<0.05）.  Conclusion  The change of antioxidant and immune indexes shows that the capability of eliminating free radicals and the immune function have decreased in the Cryptosporidium andersoni-infected cows.

Key words: Cryptosporidium, Cow, Immunity, Antioxidant index