Factors influencing the activity of liver enzymes of clinically healthy dairy cows under field conditions
Wille, S.; Simon, A.; Platen, M.; Oertel, C.
Zuchtungskunde 82(2): 155-164
In this study, activities of aspartate aminotransferase (AST), glutamate dehydrogenase (GLDH) and gamma-glutamyltransferase (GGT), determined within preventive diagnostics of healthy dairy cows, were evaluated statistically. Data derived from 18 farms, where from 2003 to 2006 in total 667 and 172 blood samples from lactating and dry cows were analysed, respectively. Each data set comprises of 25 blood samples, which consists of samples of five cows from five different performance stages each. For the interpretation of enzyme activities reference values were used, which should be applied with caution, because in literature different values are given for the same enzyme. In general, 80%, 28% and 64% of lactating cows exceeded the reference. values of 10.5 U/l, 105 U/l and 27 U/l for GLDH, AST and GGT, respectively. Furthermore, the factors lactation phase, lactation number, herd, current milk yield and milk yield in the first 100 days of lactation were tested for their influence on enzyme activity. The influence of these factors was proven; however, it was very low. Only a small proportion of the observed variability could be explained by these factors. Therefore, the estimated enzyme activities of some selected animals do not certainly represent the conditions in the whole herd. Altogether, within a preventive herd monitoring on healthy cows the significance of the activity of GLDH, AST and GGT is not given. A reliable evaluation of enzyme activities is hardly possible, not only due to the general problems in using reference values but also due to the high variability of these parameters.