A viability model to assess the sustainability of mixed herds under climatic uncertainty

Abstract

On the Bolivian arid highlands, breeders' strategies combining herd diversification (llamas and sheep) and the control of breeding rate were assessed under unpredictable environmental conditions. A survey of 14 farms made it possible to characterise practices in llama flocks (controlled and uncontrolled breeding practices) and in sheep flocks (high care and low care practices). The efficiency of these practices was evaluated using annual numerical productivity indexes. To assess the effectiveness of these practices, a dynamic model of mixed herds, based on the mathematical framework of the viability theory, was developed. The model made it possible to analyse the long-term interactions between management practices and climatic uncertainty on livestock system sustainability. Numerical productivity at weaning was found to be significantly lower in llama flocks managed with controlled breeding compared to uncontrolled breeding (44% and 70% respectively). For sheep, numerical productivity at weaning of high-care flocks was not significantly higher than that of low-care ones (83% and 69%, respectively). It was not possible to conclude whether high-care practices were more efficient in increasing numbers than low-care ones. On a long-term perspective, the dynamic analysis showed that the control of the llama flock breeding rate stabilises the evolution of the mixed herd only when a low offtake rate can satisfy a minimum income. Thus, foregoing short-term yield can be a sound strategy to insure mixed herd viability in an extremely harsh and unpredictable environment. However, the effectiveness of this practice is closely related to wealth (herd size). The model is discussed in terms of its heuristic value for assessing management practices and sustainability of pastoral systems.