Ferrofluids with rod-like nano-sized magnetite particles were prepared by precipitation from aqueous solutions of ferrous hydroxide and aging them in the presence of a magnetic field. We studied the Couton-Mouton effect measuring the azimuthally distribution of the transmitted light intensity and obtained that its magnetic field dependence differs considerably for ferrofluids containing rod-like and spherical magnetic nanoparticles, respectively. After switching off the magnetizing field, the relaxation of the birefringence was observed, measured and analysed.