The aim of the proposal is to study the effect of an applied magnetic field on the magnetic excitation spectrum of the magnetocaloric compound Mn5Si3.In a previous study performed at zero magnetic field, we evidenced a markedly distinct spin dynamics between the two antiferromagnetic phases AF1 (TN1=66K) and AF2 (TN2=99K) of Mn5Si3.In particular, the higher temperature phase AF2 exhibits coexistence of diffuse spin fluctuations and well-defined spin-waves. Since the AF1 and AF2 states are associated with direct and inverse magnetocaloric effect, respectively, the proposed experiment is crucial for revealing fundamental microscopic mechanisms associated with the magnetocaloric effect.