The keeping of a maximum of four animal units shall be permitted on individual lots of five acres or more and which are entirely within the borough limits. An animal unit shall consist of one equine animal, horse, pony or donkey, or three sheep. This limitation shall not apply to colts or lambs under one year of age. Any shelter or housing to be erected for such animals shall be located a minimum of 200 feet from the side lines of the lot and a minimum of 100 feet from the front line of the lot.