Fourie, H.J.; Van Amelsfoort, A.F.; Michael, L.M.; Putterill, John Fraser(Published by the Agricultural Research Council, Onderstepoort Veterinary Institute, 1997)
Williams, R.; Schoeman, M.; Van Wyk, A.; Roos, K.; Josemans, E.J.(Published by the Agricultural Research Council, Onderstepoort Veterinary Institute, 1997)