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Abstract
1. As hens age, egg weight increases but the eggs contain proportionally more yolk and less albumen and shell. However, at a given age, larger eggs contain proportionally more albumen. When modelling the nutrient requirements of the hen over a production cycle, based on the daily outputs of each nutrient, egg weight needs to be predicted as the sum of the three components, since each has a unique chemical composition, and these proportional changes will therefore influence the nutrient requirements of the hen.
2. Yolk weight is related to hen age and may be calculated using a logistic or Gompertz function. Allometric functions are used to predict albumen weight from yolk weight and shell weight from the weight of the egg contents.
3. A mechanistic, stochastic population model for layers may be used to verify that these functions correctly reflect the proportional changes in the egg components with advancing hen age and at a given age, over a range of egg weights.
4. The various parameters used in the equations need to be defined for the available genotypes.