Abstract
We investigated the use of concentrations of blood-serum amino acids to assess status of dietary proteins of juvenile cotton rats ( Sigmodon hispidus ). Eighteen juvenile animals were randomly assigned to isocaloric diets containing 4 or 16% crude protein, and serum concentrations of amino acids were determined by high-pressure liquid chromatography on days 30 and 45 of a 45-day feeding trial. Concentrations of methionine, threonine, tryptophan, valine, hydroxyproline, and branch-chain amino acids (BCAA) were depressed, whereas histidine and proline were elevated among low-protein-fed cotton rats. The glycine/(leucine + valine) and phenylalanine/tyrosine ratios were greater in serum of cotton rats fed low-protein diet, whereas the tyrosine/neutral amino acids (NAA) and tryptophan/NAA ratios were depressed. Concentration of several free amino acids in serum of juvenile cotton rats differed between 30- and 45-day samples. Because diet × sample interactions were significant for only tryptophan and hydroxyproline, temporal changes probably were a reflection of age-related alterations in developmental physiology and not effects of diet. Our results indicate that clinical profiles of selected amino acids in serum can provide a useful technique for assessing protein nutritional status and quality of diet in small mammals.
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