For the first time, the pinning effect of small spheroid particles with aspect ratios 1, 2 and 3 on grain growth in polycrystalline structures was studied by three-dimensional phase field simulations. This was possible by using an efficient parallel sparse bounding box algorithm. Simulation results for different volume fractions of the second-phase particles show that distributions of particles with higher aspect ratios have a stronger pinning effect, since grain boundaries have the tendency to align with the largest cross-section of the particles. The number of particles at triple, quadruple or higher order junctions increases with volume fraction, and with aspect ratio. Nevertheless, the final grain size has a volume fraction dependence of the form 1/f_V^0.93, following theoretical predictions assuming random intersections between grain boundaries and particles. A generalised Zener relation with a prefactor depending on the aspect ratio is proposed.