Abstract:
Chickens, being open thermodynamic systems, maintain a constant exchange of energy
and matter with their surrounding environment. In order to avoid reaching
thermodynamic equilibrium with the environment the bird makes use of homeostatic
mechanisms. These ensure the reduction of the entropy of the system to values that
guarantee its integrality.
The thermoregulatory response is a major component of the homeostatic machinery of
living systems. This induces modifications of physiological parameters of the bird,
taking the system “bird” to a new steady state. The achievement of this new state is
possible only if the thermoregulatory mechanisms of the birds are able to counteract the
environmental demand/burden. A successful thermoregulatory response depends not
only on the achievement of that steady state, but also on the compatibility of the value
of those parameters with life (especially regarding the value achieved by body
temperature) as well as on the time of exposure to the environmental perturbation.
Based on those premises, this thesis presents a mechanistic analysis of the thermal
interaction between a broiler and its surroundings. The first section of the document
introduces the reader to the general concepts of thermodynamics of living systems and
physics of heat exchange. The second use mechanistic simulation techniques to represent
the environment, the thermal and thermoregulatory properties of a broiler chicken and
the interaction between bird and environment. Finally, the third section describes a
conceptual simulation model able to predict, over a given period of time, the response of
a bird to environmental conditions above those associated with least thermoregulatory
effort. Various simulation exercises are reported, the objectives being to study the
behaviour of certain variables and to question the validity of current theories of
thermoregulation in environmental physiology.
