Amino Acid Compositions of Body and Milk Protein Change during the Suckling Period in Rats1

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ABSTRACT

The amino acid concentrations of rat body protein and rat milk protein were measured at 1, 6, 10 and 16 d of age to determine whether the concentration of each amino acid in proportion to the concentration of total recovered amino acids (amino acid composition) in the body changes during early growth and development and whether parallel changes occur in the amino acid composition of milk. The ratio of essential to nonessential amino acids in bodies decreased 10% during the suckling period (P < 0.05). The ratio of essential to nonessential amino acids in milk proteins decreased by 6% (P < 0.05). With the exception of threonine, the body to milk ratio for each essential amino acid seemed similar to that for the other essential amino acids, implying that most essential amino acids are equally limiting for the synthesis of body protein in exclusively milk-fed pups. Measurements of milk intake and milk composition were used to determine amino acid intakes and hence the efficiency with which milk amino acids were used for body protein deposition. The efficiency of essential amino acid utilization was 75% between 1 and 6 d, 86% between 6 and 10 d, and 62% between 10 and 16 d of age. Although the overall efficiency of nonessential amino acid utilization showed a similar pattern, the results suggested the need for a high degree of glycine and arginine synthesis.

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    1

    This work is a publication of the U.S. Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine and Texas Children's Hospital, Houston, TX. This project was funded in part with federal funds from the U.S. Department of Agriculture/Agricultural Research Service under Cooperative Agreement no. 58-6250-1-003. The contents of this publication do not necessarily reflect the views or policies of the U.S. Department of Agriculture, nor does mention of trade names, commercial products or organizations imply endorsement by the United States Government.

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    Copyright © 1993 American Society for Nutrition. Published by Elsevier Inc. All rights reserved.