Botha, C.J. (Christoffel Jacobus); Kellerman, T. Stephanus; Schultz, R.A. (Rowena Anitra); Erasmus, G.L.; Retief, E.P.(Published by the Agricultural Research Council, Onderstepoort Veterinary Institute, 1998)
Scholtz, M.M.; Spickett, Arthur M.; Lombard, P.E.; Enslin, C.B.(Published by the Agricultural Research Council, Onderstepoort Veterinary Institute., 1991)