We consider the couples (M, 0) where M is an odd-dimensional compact manifold with boundary, endowed with a non-singular Morse-Smale flow 0, satisfying some given homological boundary information. We compute, in terms of that information, a number pmin such that any non-singular Morse-Smale flow 0 on any manifold M satisfying the given abstract homological data must have at least pmin closed periodic orbits. Moreover, we provide, for any initial homological data, a non-singular Morse-Smale model (M0, 00) for which pmin is attained. In the general case of a couple (M, 0) satisfying the given homological information, such a number pmin is a lower bound. The algorithm underlying this computation is based on optimization theory in network flows and transport systems.