  We propose a new model for the time evolution of livestock commodities which
exhibits endogenous deterministic stochastic behaviour. The model is based on
the Yoccoz-Birkeland integral equation, a model first developed for studying
the time-evolution of single species with high average fertility, a relatively
short mating season and density dependent reproduction rates. This equation is
then coupled with a differential equation describing the price of a livestock
commodity driven by the unbalance between its demand and supply. At its birth
the cattle population is split into two parts: reproducing females and cattle
for butchery. The relative amount of the two is determined by the spot price of
the meat. We prove the existence of an attractor and we investigate numerically
its properties: the strange attractor existing for the original
Yoccoz-Birkeland model is persistent but its chaotic behaviour depends also
from the price evolution in an essential way.
