Estimators of body nitrogen in growing rats fed varying levels and qualities of protein.
The relationships between total body nitrogen and body weight, carcass water and carcass [body minus gastrointestinal (GI) tract] nitrogen were investigated with Sprague-Dawley rats fed diets containing casein, peanut flour or wheat gluten as protein sources. Twelve diets containing 2-31% of each protein fed to groups of six (12 for protein-free diet) weanling rats for 4 weeks. The animals were killed by sodium pentobarbital injection and weighed. GI tracts were removed and washed free of their contents. Carcass water was determined by oven drying; carcass and GI tract nitrogen were determined by Kjeldahl analysis. Linear regression equations for each relationship and protein closely fit the data (r2 greater than 0.9). In each relationship the equations for casein and peanut protein were not significantly different (P less than 0.05), but both were different from the equation for gluten. Despite high r2 values, plots of deviations from regression showed a distinct pattern in several cases. Quadratic equations relating body nitrogen to the other parameters gave improved fit of the data in most instances. Quadratic equations for a given relationship were not significantly different for the three proteins. Net protein utilization (NPU) values based on body nitrogen estimated by linear equations were significantly different from those based on determined values in several cases. When quadratic estimating equations were used, the values were different only in one case.
D000818:Animals; D001823:Body Composition / Q000187:drug effects; D001834:Body Water / Q000378:metabolism; D001835:Body Weight / Q000187:drug effects; D004044:Dietary Proteins / Q000494:pharmacology*; D009584:Nitrogen / Q000378:metabolism*; D051381:Rats
D004044:Dietary Proteins; D009584:Nitrogen