A Proto-type Dynamic Model of the Australian Sheep

Abstract: The sheep meat industry experiences production variability associated with climatic inputs, policy signals and flock management. It is apparent that driven by the buoyant markets and a run of good seasons coming into the new century, the industry was extracting increasing numbers of potential breeding females from the flock to market as sheep meat. This may have long-term implications for flock dynamics, particularly the ability of the flock to recover from a drought, exploit market opportunities or manage disease. The challenge was to develop a simple, inexpensive yet robust model as a way of evaluating, and possibly predicting long term flock decline. This prototype is a deterministic model using a simple projection matrix (6-age, 2-sex structure). The vital rates of the flock were estimated using a Delphi technique with 5 key producers in the industry. This model was able to hind cast the flock decline evident in national level Australian Bureau of Statistics records. Sensitivity and Eigen-analysis of the flock growth rate pointed to the survival and reproductive output of two and four year old merino ewes as being important determinants of the decline. This simple approach was also extended to include year-to-year production variability and the inter-regional migration of sheep. Collectively these prototype models demonstrate that it is possible to undertake simple projections of the national flock and ask ‘what-if ’ questions to explore a range of plausible outcomes. The approach require