Alanine aminotransferase (ALT), aspartate aminotransferase (AST), γ-glutamyl- transferase (GGT), and alkaline phosphatase (ALP) are important catabolic enzymes, which play an important role in liver function of animals. The activities of these enzymes were monitored in milk and blood plasma and association between them was determined through regression analysis. Samples of milk and blood were collected from 35 housed multiparous Holstein cows 3-9 weeks postpartum. The results showed that there were significantly positive correlations for these four enzymes between the enzyme activities in milk and blood plasma (ALT, r_s=0.852, Ρ<0.001; AST, r_s=0.341, Ρ<0.001; GGT, r_s=0.628, Ρ<0.001; ALP, r_s=0.707, Ρ<0.001). Compared to the blood plasma, the activities of ALT (Ρ<0.05) and AST (Ρ<0.001) in milk appeared significantly lower, while the activities of GGT and ALP were significantly higher (Ρ<0.001). With the regression models, it seems that detection of ALT, AST, GGT and ALP activities in milk may be an alternative way to monitor the liver function of cows. Therefore, this study is an initial step for studying the liver function through detection of these enzymes in milk.

Key words: Blood plasma, Hepatic enzymes, Holstein cows