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Effect of Fasting and Level of Dietary Protein on Free Amino Acids in Pig Plasma^{1, 2,}

Texas A&M University, College Station

Abstract

The concentrations of 17 free amino acids were determined in pigs that received three dietary treatments. In one test the animals were fasted for 12 and 24 hr. In a second test the animals were fasted for 18 hr. and then fed a single test meal with amino acids being determined in plasma at zero, 3, 6 and 9 hr. after the meal was fed. In the third test animals received a purified diet containing zero, 15 or 30% protein from purified soybean protein. The amino acids were consistently lower in plasma of animals fasted for 12 hr. than they were in those fasted zero or 24 hr., but none of the differences was significant. Similarly, none of the differences in the amino acids of plasma of animals in the fasting and refeeding test was significant.

In the experiment involving the level of dietary protein, significant increases in glutamic acid, isoleucine, leucine, ornithine, threonine, tyrosine and valine occurred as the protein level increased. No significant effect or trends in concentration of aspartic acid, glycine, histidine, lysine, methionine, phenylalanine, proline and serine resulted from the changes in level of dietary protein.

¹ Departments of Biochemistry and Nutrition and of Animal Husbandry, Texas Agricultural Experiment Station, College Station.

² The authors gratefully acknowledge Merck & Co., Rahway, N. J., for vitamins; Lederle Laboratories, Pearl River, N. Y., for folic acid; and the Texas Division of Dow Chemical, Free-port, Texas, for DL-methionine. They also gratefully acknowledge the technical assistance of Patricia Lauderdale and Martha Cannon in taking blood samples and running the amino acid analysis.

³ Present address: Department of Home Economics, Virginia Polytechnic Institute, Blacksburg, Va.