Animal husbandry and livestock farming; provided, that not more than one horse, mule, cow, or steer, shall be kept for each twenty thousand square feet of area and no more than one goat, or one hog, or one sheep or similar livestock shall be kept for every seven thousand square feet of area. Such area requirements shall not include the special setback requirements of this title, nor the area occupied by the main building. Additionally, the density limitations listed above shall not apply to targeted grazing, provided said targeted grazing lasts no longer than thirty days in any single calendar year on any single parcel;