A two-stage stochastic programming model for scheduling replacements in sow farms

Abstract

This paper presents a formulation and resolution of a two-stage stochastic linear programming model with recourse for sow farms producing piglets. The proposed model considers a medium-term planning horizon and specifically allows optimal replacement and schedule of purchases to be obtained for the first stage. This model takes into account sow herd dynamics, housing facilities, reproduction management, herd size with initial and final inventory of sows and uncertain parameters such as litter size, mortality and fertility rates. These last parameters are explicitly incorporated via a finite set of scenarios. The proposed model is solved by using the algebraic modelling software OPL Studio from ILOG, in combination with the solver CPLEX to solve the linear models resulting from different instances considered. The article also presents results obtained with previous deterministic models assessing the suitability of the stochastic approach. Finally, the conclusions drawn from the study including an outlook are presented.

Sara V. Rodríguez would like to thank CONACYT (Consejo Nacional de Ciencia y Tecnología, Mexico) and the Department of Universities and Information Society (autonomous government of Catalonia, Spain) for the grant received during the development of this study. Victor M. Albornoz wishes to acknowledge the Dirección General de Investigación y Postgrado of the Universidad Técnica Federico Santa María, Grant USM No. 28.08.52. Lluís M. Plà wishes to acknowledge the financial support of the Spanish Research Program (MTM2005-09362-C03-02).