If not animated:
Edit modeEdit mode
Menu: Mesh » BisectMesh > Bisect
clickClick and select options at left (tT tools panel on 3d viewin 3D View), like fill or quit parts. Get it from: http://wiki.blender.org/index.php/Doc:2.6/Manual/Modeling/Meshes/Editing/Subdividing/Bisect
The boolean operations always try to conserve the mesh.