1. Heitzman, R.J.: In Environmental Quality and Safety. Coulston, F., Korte, F. (eds.) Suppl. Vol. 5, p. 89. Stuttgart: Thieme 1976
2. Heitzman, R.J., Chan, K.H., Hart, I.C.: Br. Vet. J.133, 62 (1977)
3. Grandadam, J.P., Scheld, A., Jobard, A., Dreux, H., Boisson, J.M.: J. Anim. Sci.37, 256 (1973)
4. Koers, W.C., Parrott, J.C., Klett, R.H., Sherrod, L.B.: J. Anim. Sci.39, 243 (1974)
5. Kilkenny, J.B., Sutherland, J.E.: Vet. Rec.87, 743 (1970)