A model of calcium and phosphorus growth in broilers.
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Date
2022
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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.
Description
Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.