De Vos, Valerius; Bengis, Roy G.; Kriek, N.P.J.; Keet, D.F.; Raath, J.P.; Huchzermeyer, Hildegard F.A.K.
(Published jointly by the Agricultural Research Council, ARC-Onderstepoort Veterinary Institute and the Faculty of Veterinary Science, University of Pretoria., 2001)