The N:H2O ratio in the Sprague–Dawley rat and its variation with diet under the conditions of determination of net protein utilization

Abstract

1. Analytical values are presented for body nitrogen, both on a fresh and dry carcass basis, body water and N to body water ratios for rats, of various ages, of the Sprague–Dawley Strain.2. For 33- and 40-day-old animals, there were significant differences in body composition, including N:H₂O ratio, between animals given a protein-free diet and those given protein at the 10% dietary level. For all age groups the N and water percentages were higher in the carcasses of animals given the non-protein diet.3. For all age groups there were significant negative correlations between the percentage of N in the dry carcass and the net dietary protein value (NDpv) of the diet. For 33-, 37- and 40-day old animals there were significant negative correlations between the N content of the fresh carcass and the NDpv of the diet. For 33-day-old animals only, the correlation between N:H₂O ratio and NDpv was also highly significant.4. Body N values calculated from N:H₂O ratio and from N:body-weight ratio were compared. At all ages, an equally good prediction was obtained from the N:body-weight ration as from the N:H₂O ratio provided that the correct factors were used for animals given the non-protein and test diets.