Farm animals shall only be kept in an agricultural district of the city, or on a residential lot of at least ten acres in size provided that no animal shelter shall be within 300 feet of an adjoining piece of property. An exception shall be made to this subsection for chickens kept on residentially zoned properties in accordance with this section and those animals brought into the city as part of an operating zoo, veterinarian clinic, scientific research laboratory, or a licensed show or exhibition.