T.H.Cluton-Brock, J.P.Greenwood and R.P.Powell, 1976, "Ranks and Relationships in Highland Ponies and Highland Cows," Zeitschrift Tierpsychologie, 41, 202-216.
M.W.Schein and M.W.Frohman, 1955, "Social Dominance Relationships in a Herd of Dairy-Cattle," British Journal of Animal Behaviour, 3, 45-55 (1955).