The behaviour of serum LDH isoenzyme activity in patients, towards injected antibiotics and breeds of dairy cows

The present study consists of 3 experiments. In the first experiment, blood serum LDH isoenzyme activity was assessed in 8 dairy patients with energy metabolism disorders. Total mean serum AST, GGT, and ALP activities were higher in all patients. Relatively higher total mean serum LDH activity was found in cows 1, 3, and 6 (9.06+-2.94; 12.23+-1.30; 9.65+-1.96, respectivelyThe most variable serum isoenyzme was LDH3 ranging from 4.15+-1.95% to 25.83+-1.51% of the total activity. Relatively high mean serum percentage LDH4 isoenzyme activity was found in cows 2, 6, and 7 (5.14+-1.90; 2.74+-1.56; 2.70+-2.04, respectively), while in cow 3 it was undetectable. Percentual LDH5 isoenzyme activity was not detected in any of the sera of the animals examined. Cows 1-7 showed a complete lack of effective clinical response to the therapy. In cow 8, however, total AST, GGT, and LDH activity declined after four weeks of therapy. During the first four weeks of therapy the liver isoenyzmes, LDH4 and LDH5, were undetectable. After the fifth week of therapy, however, they were detected. By the histopathological analysis of the first liver biopsy sample perilobular lipid hepatic dystrophy was found, but in the second biopsy sample only rare fat droplets without observable pathological changes in hepatocytes were found. In the second experiment, the possibility that the injected antibiotics might inhibit the activity of the more sensitive LDH4 and LDH5 isoenzymes was investigated in 3 dairy cows. The blood samples collected before, then at 6 and 72 h after Tetradura LA-300 (Merck & Co., Inc., U.S.A.) administration were analysed. The highest mean percentage LDH5 activity was found in the serum collected 6 h after the treatment, whereas the lowest activity was determined in the serum taken 72 h after the treatment. On the other hand, LDH4 activity was higher in the serum obtained before the treatment and was lower in the serum collected 72 h after the treatment. In the third experiment, in order to investigate the influence of breed on the presence or absence of serum LDH5 isoenzyme activity in some healthy dairy cows, the serum taken from 18 dairy cows of different breeds was assayed. In each breed group two of the six animals had detectable LDH5 isoenyzmes. From our results we can conclude that LDH4 and LDH5 isoenzyme activity in the serum obtained from dairy cows with chronic lipid hepatic dystrophy and from dairy cows treated with a long-acting antibiotic was undetectable. However, shortly after the administration, when the antibiotic blood level reached its highest peak, markedly increased serum LDH4 and LDH5 isoenzyme activity was observed. Therefore liver isoenzymes LDH4 and LDH5 are not elevated in chronic diseases and in sera where they are exposed to oxytetracycline for a long time. Hence, in using LDH isoenzymes as a diagnostic aid or for research purposes, these facts should be taken into consideration. Further, the presence or absence of LDH5 isoenzyme in the sera taken from some healthy dairy cows is not dependent upon breed