Net utilization of various levels of whole egg protein in pregnant rats

Net protein utilization (NPU) was examined in pregnant rats fed various levels (1, 3, 6, 10 and 20%) of whole egg protein (WEP), based on their obligatory nitrogen losses. On increase in dietary protein, nitrogen balance improved curvilinearly and the NPU decreased exponentially in both pregnant and nonpregnant rats. The utilization efficiency was high in rats fed marginally low protein diets, mainly due to lower urinary nitrogen levels than the obligatory levels of nitrogen loss. The NPUs in pregnant rats fed 1, 3, 6, 10 and 20% WEP diets were 103, 99, 78, 66 and 46, respectively. These values were 15 to 20% higher than those in nonpregnant rats because in pregnant rats obligatory urinary nitrogen loss was higher and the animals took more energy. The problems in application of the NPUs in pregnant rats for estimating the protein allowance of pregnant humans are discussed.