A model of calcium and phosphorus growth in broilers.

Abstract

A model is a simplified representation of a system. It can be used to organise knowledge and to develop theory in an academic setting, but also for practical applications. This research sought to incorporate as much as possible of the theory of calcium and phosphorus in broiler chickens into a model. This would allow researchers to see where there are gaps in the theory and to suggest ways in which experiments might be designed to fill these. It is hoped that this model will provide a guide for producers when they feed broilers, particularly under changing conditions. Current tables of requirements reflect empirical data on bird performance, collected at a certain point in time. As genetic progress, welfare considerations and environmental pressures change the constraints on an animal production system, a dynamic model allows the nutritionist to be more responsive to these. The calcium/phosphorus model is located within an existing broiler model that simulates energy metabolism and protein growth. This model is linked to a feed formulation component and an optimiser that allows producers to manage their enterprise to meet production and profit targets. Because standardised digestibility values have proved elusive for minerals, a digestibility module assesses the complete feed and calculates mineral quantities available to the bird. These are then assessed against the requirements for soft tissue which is given priority and then bone growth. Excess mineral is excreted and this, and bone mineralisation are considered for the optimiser module of the main model. The model was calibrated and validated using two body composition studies. It was demonstrated that reasonable predictions of performance could be made, but that modelling digestibility is a critical component. Perhaps most importantly, the model maps a way forward for research targeted at filling the gaps in the body of knowledge. These have been shown to be surprisingly large: very little whole carcass body composition work has been done and few studies of calcium and phosphorus digestibility have been designed to allow modelling of their interactions.