So far as practicable those in custody on an industrial farm shall be employed in productive labor. The products of an industrial farm shall be used: first, to maintain the prisoners and employees on such farm; second, to supply other county institutions having need of the same with the farm’s products; third, to supply the needs of paupers, incompetents, poor and indigent persons and those incapacitated by age, disease or accident with whose relief and support the county is charged.