Biotin-Binding Proteins in Chicken Eggs and the Biotin Requirements of Chicken Embryos

In addition to avidin in albumen, chicken eggs contain another biotin-binding protein in yolk. The amounts of these two proteins were monitored in the eggs of nine broiler breeder hens over a several month period. Although the hens were of the same stock and age, fed the same diet, and housed together, there was a two to threefold range in the amounts of these proteins in eggs from different hens. The average binding capacity of avidin for the eggs from single hens ranged from .70 to 2.16 μg biotin/ml of albumen while that for biotin-binding protein ranged from .22 to .50 μg biotin/ml of yolk. There was only a weak correlation between the amounts of the two proteins in different eggs from a single hen and no correlation in the average amounts of the two proteins in the eggs from different hens. The biotin-binding protein content of egg yolk is related to the nutritionally determined biotin requirements for hatchability in chicken and may be a predictor of biotin requirements for hatchability in other avian species.