I believe Lord Derby Eland is a synonym for Giant eland, also regarding subspecies of Giant eland, there are 2 recognized subspecies and those subspecies are the Western giant eland (Taurotragus derbianus derbianus) and the Eastern giant eland (Taurotragus derbianus gigas), as far as I am aware, there are no Western giant eland in captivity because they are an InSitu species, but all the Giant elands that have been in captivity in Europe and North America are Eastern giant elands