**3.1 Aspartat Aminotransferase (AST)**

The enzyme AST is present in different tissues and is a sensitive indicator of soft tissue damage. In heart and skeleton musculature as in liver there is high activity of AST. The AST is present in cytoplasm and in mitochondria so its activity is increased chiefly by cell necrosis in smaller amount also by damage of the cell membrane (Kraft & Dürr, 1999a). Measuring of AST activity in combination with CK is used for diagnostics of muscle damage (Kaneko, 1997). High activity of AST is also in liver and in the case of liver damage AST activity in serum increase.

After first colostrum intake the AST activity in serum increased from 23 U/L before intake, to 38 U/L at the age of 3 hours, what is most likely due to absorption from colostrum or because of activation of enzymes in calf intestine as consequence of colostrum intake (Kurz & Willet, 1991). However Hammon and Blum (1998) established that in calves which received only milk replacer instead of colostrum, activity of AST increased on the second day after birth so they are of the opinion that also other factors influence on the increased activity of some enzymes. The activity of AST decreased after the first week, and from 42nd to 84th day of life it increased slowly (Egli & Blum, 1998). Mohri et al. (2007) observed the increase of AST activity from the 14th to the 84th day of age.
