I think niuweidao is the general term for the many broad bladed, sabers with a raised yelman, while "manchu dao" may be more of a collectors term. Manchu dao are certainly a recognizable subset of the oxtail style, and the scabbards are similar to Qing regulation scabbards for the willow leaf swords of the regular army. It is not wild speculation to suppose that there were regular militia under Manchu control that used these swords. Nevertheless, until a militia regulation manual terns up, I will put this term with other collector’s terms for recognizable types, such as the Qijiadao, that may have some historical basis, but are unsubstantiated.
Just for reference, here are some niuweidao that are not of the "Manchu dao" type, mixed with some other civilian dao.
http://i77.photobucket.com/albums/j6...i/DSC_1053.jpg
http://i77.photobucket.com/albums/j6...duation357.jpg
Josh