[Gamma-glutamyltransferase in the blood of cattle].

Information is given on a long-term observation of gMT activities in the blood of cattle, aimed at using the results to interpret metabolic tests, especially tests of the function of liver. Dynamics of changes in the gMT activities was studied in the year seasons and the per cent activities in the decades (from 20 to 100 U per 1) in different groups of cows according to their reproduction cycle. In the part discussion relationships are given between the gMT activities and other findings obtained from metabolic tests. The average value of the gMT activities in the blood of a reference group of cows was 30.7 U per 1. The standard deviation was 7.01 U per 1. Reference limits for the gMT activities in the bovine blood serum - 16.7 to 44.7 U per 1 (95% interval of confidence) could be determined by a parametric statistical method. Average deviations of the gMT activities from those in the reference group of cows, expressed in histogram units J, ranged from 0.03 to 1.07 J after a long-term observation in particular calendar months. The maximum positive deviations were observed in January, June, July, November and they indicate the risk period, in August and September the values nearly approached those in the reference group of cows. The maximum positive deviation of the metabolic test amounted to 6.8 J (January). There were eight metabolic tests with the deviation greater than 1 J during the observation, two in the summer period (May--October) and six in the winter period (November-April). In cows after calving and in the first half of gravidity the gMT activities were most frequently in the decade 30.5-40.0 U per 1, and in highly pregnant cows in the decade 20.5-30.0 U per 1.