A Method of Determining the Biological Value of Protein in the Study of Avian Nutrition

The endogenous and metabolic nitrogen elimination of S.C. White Leghorn chicks has been studied from time of hatching to twelve weeks of age. Twenty chicks were used in each lot studied. The urinary nitrogen was calculated from the sum of the uric acid nitrogen and ammonia nitrogen elimination by multiplying by 1.25. The per cent of total nitrogen and uric acid eliminated varies from day to day but the total amount per day is nearly the same throughout the period. The total fecal nitrogen is comparatively small in amount and decreases somewhat during the nitrogen-free period. The fecal nitrogen per kilogram of food intake varies from day to day, but remains at about the same level throughout the period. Calculated per kilogram of body weight, the fecal nitrogen decreases in the latter part of the period. The response of chicks to a low nitrogen diet and to the resumption of a commercial ration is shown. Within the twelve-week period following hatching no variation of either fecal or urinary nitrogen was found which correlated with the age of the chicks. The averages for the six lots were accepted for use in calculating biological values. A method of calculating the biological value of protein for use with poultry is presented.