Applicability to Chicks of the Carcass Analysis Method for Determination of Net Protein Utilization

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Abstract
Feeding experimental diets at 4 protein levels (7.5, 10, 12, 5 and 15%) had no significant influence on the regression relationship between carcass nitrogen and water content of chicks. A study of the effect of protein level on net protein utilization (NPU) and net protein ratio (NPR) involving 5 different protein sources, each fed at 4 supplementation levels, showed that the diet containing 10% protein consistently resulted in the highest NPU and NPR values for all the proteins under test. The conversion factor required to calculate protein retention efficiency (PRE) from NPR was found to be independent of the protein level in the experimental diet. A distinct difference exists between the conversion factor to be used for rats and chicks, respectively. The practical importance of PRE derived from weight gains during a 9-day experimental period as an estimate of NPU is discussed. The effect of varying levels of starch, (10, 20 and 30%), oil (4, 8 and 12%) and cellulose (zero and 4%) on the NPU value of a 10% casein diet was tested in a factorial experiment. The NPU value was not influenced significantly by either calorie level or fiber level. Substitution of 20% of sucrose in the experimental diet with cornstarch resulted in significantly higher NPU and NPR values.