We investigated the use of concentrations of blood-serum amino acids t
o assess status of dietary proteins of juvenile cotton rats (Sigmodon
hispidus). Eighteen juvenile animals were randomly assigned to isocalo
ric 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 methion
ine, threonine, tryptophan, valine, hydroxyproline, and branch-chain a
mino acids (BCAA) were depressed, whereas histidine and proline were e
levated among low-protein-fed cotton rats. The glycine/(leucine + vali
ne) and phenylalanine/tyrosine ratios were greater in serum of cotton
rats fed low-protein diet, whereas the tyrosine/neutral amino acids (N
AA) 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 x sample interactions were signific
ant for only tryptophan and hydroxyproline, temporal changes probably
were a reflection of age-related alterations in developmental physiolo
gy and not effects of diet. Our results indicate that clinical profile
s of selected amino acids in serum can provide a useful technique for
assessing protein nutritional status and quality of diet in small mamm
als.