The Influence of Protein and Energy Intakes Upon Nitrogen Retention in the Pregnant Rat ,

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Abstract
A comparison was made of nitrogen retentions in groups of laboratory rats on two levels of dietary protein and two levels of energy intake during the second and third weeks of pregnancy. Differences in the metabolic needs of the maternal organism between the second and third weeks of pregnancy were reflected in the utilization of the protein and energy supplied by the diets. On the low protein-low calorie diet, the factor limiting nitrogen retention during the second week of pregnancy appeared to be the non-protein calorie intake, whereas during the third week the protein intake appeared to be limiting. On the high protein-low calorie intake, there was little correlation of either nitrogen intake or non-protein calorie intake with nitrogen retention during either week of pregnancy, and the data indicate the use of dietary protein for energy purposes. During each of the weeks of pregnancy studied, the highest percentage of nitrogen retained was associated with the highest non-protein calorie intake. Strong correlations of nitrogen intake or non-protein calorie intake with nitrogen retention were apparent when the non-protein calorie intake was high. It is suggested that nitrogen retention during pregnancy, rather than the birth weight of the young, be considered the criterion of the adequacy of a diet for reproduction in the rat.