title: Carcass nitrogen as a predictor of protein requirement for mature female rats.
abstract: The minimal level of dietary protein required for maintenance of nitrogen equilibrium was investigated using Sprague-Dawley rats, 12 months of age. Rats were fed casein, supplemented with methionine, at levels ranging from 0.84 to 5.18% of the diet for 4, 8 or 12 weeks and were compared to a control group fed a similar diet containing 9.90% protein or to a baseline group fed a stock diet. The effect of dietary protein levels on total serum protein and on liver and carcass composition was assessed. Protein requirement levels with 95% confidence intervals were predicted by linear regression. Dietary protein levels of 2.14% or lower were not adequate to maintain body weight and serum protein levels, and animals fed these diets had elevated levels of liver lipid. Protein nutriture of rats fed 3.20% protein was generally intermediate between those fed 2.14% or less and those fed 3.62% or greater. Compared to carcass nitrogen, carcass water was not as reliable a parameter for determination of protein requirements. Using the baseline group for comparison and carcass nitrogen as the dependent variable, a dietary protein requirement was predicted for these animals of 3.91--4.19% with confidence intervals of 3.50--4.56% and 3.13--5.48%, respectively. This level is comparable to the maintenance protein requirement of 4% indicated by the National Research Council for adult rats.
mesh_terms: D000818:Animals; D001798:Blood Proteins / Q000378:metabolism; D001823:Body Composition / Q000187:drug effects*; D002364:Caseins / Q000008:administration & dosage; D004044:Dietary Proteins / Q000008:administration & dosage*; D005260:Female; D008099:Liver / Q000378:metabolism; D008297:Male; D008715:Methionine / Q000008:administration & dosage; D009584:Nitrogen / Q000378:metabolism*; D009751:Nutritional Requirements; D051381:Rats; D012044:Regression Analysis
chemical_list: D001798:Blood Proteins; D002364:Caseins; D004044:Dietary Proteins; D008715:Methionine; D009584:Nitrogen