In the design of Wireless Sensor Networks (WSNs), energy conservation is a goal at all system levels, from the application down to the hardware. This paper focuses on networklevel opportunities for energy conservation, with emphasis on the multi-hop transmissions, topology control and routing-level issues. Specifically, the paper considers energy efficient information broadcasting in WSNs deploying co-operating nodes which by adjusting their transmission ranges minimize the total transmitted power in the network. To this end, the design of routing protocols with a single relay is proposed for multiple multicast sessions in a network with randomly distributed nodes. The protocols take advantage of topological diversity created by adapting the transmission power and exploit the benefits of network coding in a system where nodes are periodically generating data packets. Energy efficiency of the conventional, store-and-forward, and network coding based relaying schemes is analyzed in different propagation conditions and for various node densities.