Keeping of cattle, sheep, goats or horses on a lot or parcel of land having an area of not less than two acres; provided, that not more than two such animals per acre are permitted, including the supplementary feeding of such cattle, sheep, goats or horses; provided further, that such grazing is not a part of nor conducted in conjunction with any dairy, livestock feedyard, livestock sales yard or commercial riding academy located on the same premises. No buildings, structures, pens or corrals designed or intended to be used for the housing or concentrated feeding of such stock shall be used on the premises for such grazing other than racks for supplementary feeding, troughs for watering or incidental fencing;