Van Aswegen, G.; De Vos, Valerius; Schoeman, J.H.; Van Noorden, Susan; Kotze, Sanet H.(Published by the Agricultural Research Council, Onderstepoort Veterinary Institute, 1996)
Odendaal, M.W.; Pieterson, P.M.; De Vos, Valerius; Botha, A.D.(Published by the Agricultural Research Council, Onderstepoort Veterinary Institute., 1991)