There is hereby authorized a “Sheriffs’ Retirement Fund” which shall be under the management of a board of directors described in section 57.958. The board of directors shall be responsible for the administration and the investment of the funds of such sheriffs’ retirement fund. Neither the general assembly nor the governing body of a county shall appropriate funds for deposit in the sheriffs’ retirement fund. If insufficient funds are generated to provide the benefits payable pursuant to the provisions of sections 57.949 to 57.997, the board shall proportion the benefits according to the funds available.