The paper presents a model of the New Zealand Sheep Industry which predicts animal numbers in various sex/age categories. The explanatory variables used are the prices of the end products of the industry and time, to represent technological change. Prices are found to have a significant, though delayed, effect on farmers' stock decisions. Furthermore, the significance of time demonstrates improvements in some forms of animal husbandry. The relative failure of the model's latest predictions emphasizes the importance of irrational optimism in the industry.