The effect of protein intake on the activities of liver specific enzymes in the plasma of dairy cows.

Activities of glutamic dehydrogenase (GLDH), sorbitol dehydrogenase (SDH) and ornithine carbamyl transferase (OCT) were determined in tissues of six cattle after slaughter. The liver contained the highest activities of all three enzymes and the kidney cortex also contained high activities of GLDH and SDH. Activities of OCT were negligible in tissues other than liver. GLDH and OCT activities were determined in plasma of two groups of cows fed different levels of protein during the pre-calving period and up to 14 weeks post calving. In both groups activities of both enzymes increased after calving, reaching three to seven times pre-calving levels between seven and 17 weeks post calving and declining thereafter. Activities of both enzymes reached higher levels in the group fed protein to conform to the recommendations of the ARC (1965) than in the group fed 25 per cent below these recommendations. One--conventional--interpretation of this would be that higher intakes of proteins were associated with pathology of liver cells but other interpretations cannot be ruled out entirely.