Spontaneous magnetization Ms of the ferromagnetic compound Mn5Ge3 with the Curie temperature TC=305 K has been studied in the temperature range from 2 to 400 K. The relationships between the magnetic part of the heat capacity (CMAG), the magnetic part of the volume thermal expansion coefficient (TEC) βMAG, and the Ms for the compound Mn5Ge3 have been considered. It has been found that the magnetic part of the heat capacity can be well approximated by the dependence CMAG(T)=a×|dM s2/dT|-b×|dMs4/dT| with a>0 and b>0, and the magnetic part of the TEC, by the dependence β MAG=C1×dMs2/dT+C 2×dMs4/dT with C10 in the whole temperature. It is assumed that the main sources in the formation of the observed CMAG(T) and βMAG(T) dependences are the changes in the elastic, magnetoelastic, magnetovolume, and magnetostatic energies of the sample that appear as a result of the spontaneous magnetostrictive deformation with temperature changing.