Improvement of the Procedure to Determine Gross Protein Value with Growing Chicks

Abstract

Duplicated groups of 6 White Leghorn male chicks were fed one of experimental diets containin 0, 3, 6 and 9% of additional standard or test protein to the diet of 11% protein for 6 days. A casein-amino acid mixture was used as standard, and casein and a mixture of soybean meal, fish meal and DL-methionine were tested.Before and after the experiment, the chicks were sacrificed and their carcass contents of moisture, crude protein, crude fat and gross energy were determined to calculate carcass protein retention per 100g feed eaten. Gross protein value was estimated by 7-point slope ratio assay procedure.Carcass protein content was almost constant regardless of quality and quantity of protein eaten. With over-lapped fiducial interval, gross protein values from body weight gain and from carcass protein retention were identical from statistical point of view. Error in estimating the value from body weight gain was smaller than that from carcass protein retention.Body weight of growing chicks in 6-day assay is reasonably accurate index of body protein. Estimation of gross protein value from body weight gain per 100g feed is superior to that from carcass protein retention.