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Effect of Source and Level of Dietary Protein on Liver Enzyme Systems in the Young Pig¹

Department of Animal Husbandry, Institute of Agriculture, University of Minnesota, St. Paul, Minnesota

Forty-eight young, rapidly growing, crossbred pigs were fed 8, 12, 16 or 20% protein starch-base diets, with the protein supplied by fish filet flour (FF), dried skim milk (DS) or soybean meal (SM), in an attempt to determine whether the activities of selected liver enzyme systems would reflect level and quality of dietary protein. The liver homogenates (1:5:liver:ice water) were assayed to determine the activities of xanthine oxidase (µliters O₂/hour/g wet liver), glutamic-pyruvic transaminase (mg pyruvic acid formed/30 minutes/g wet liver) and succinic dehydrogenase (mg formazan formed/30 minutes/g wet liver). Rate of gain and feed conversion efficiency were improved significantly as level of dietary protein was increased from 8 to 16%; liver weight and percentage nitrogen also increased significantly with increasing level of dietary protein. Liver xanthine oxidase activity was variable and did not generally reflect source or level of dietary protein. The activity of glutamic-pyruvic transaminase increased linearly with increasing levels of dietary protein from DS and SM. Succinic dehydrogenase activity increased linearly with increasing levels of dietary protein for all sources of protein. Liver succinic dehydrogenase activity was more closely related to average daily gain, liver weight and per cent liver nitrogen than was either xanthine oxidase or glutamic-pyruvic transaminase activity. Further, more elaborate studies are necessary to determine the usefulness of liver enzyme activities in evaluating protein quality for the young pig.

² Present address: Division of Biochemistry and Nutrition, School of Veterinary Medicine, University of Missouri, Columbia, Missouri 65201.

³ The authors wish to express their appreciation to the following for generous supplies of dietary ingredients: American Cyanamid Company, Princeton, New Jersey; Clinton Corn Processing Company, Clinton, Iowa; Chas. Pfizer & Co., Terre Haute, Indiana; Merck Sharp & Dohme, Research Laboratories, Rahway, New Jersey; and VioBin Corporation, Monticello, Illinois.

Manuscript received 2 May 1966.