Effect of genetic improvement of body weight on herd dynamics and profitability of Ethiopian meat sheep: A dynamic simulation model

Abstract

A community-based sheep breeding program has been implemented in the highlands of Ethiopia to improve the body weight of Menz sheep. It is important to evaluate the potential consequences of such a breeding strategy on herd dynamics. For this purpose, a dynamic, stochastic herd model was built. The model adopts a system dynamics methodology to study the effect of genetic improvement of body weight on herd dynamics and profitability. The length of the time horizon was 240 months (20 years). The first 120 months served as a baseline scenario, where the fattening of culled breeding rams was practiced. For the second 120 months genetic selection of body weight was introduced considering two scenarios: culled ram and lamb fattening. Results from the model showed a gradual decrease in sheep population size while body weight of the animals improved. The model keeps heavier animals in smaller flocks to match the herd dry matter demand with the available resources. The simulation also demonstrates that breeding for heavier body weight was considerably more profitable than the baseline scenario; and lamb fattening was more profitable than culled ram fattening, as the current practice. Furthermore, voluntary culling may be used to balance herd size with available feed resources. The introduction of a more intensive system that provides more feed resources by resourceful smallholders can be used to achieve higher income without reducing flock size. Further work is however needed to evaluate the model introduced here against field results.