1. Perry, K.D. &McGillivray, W.A., 1964. J. Dairy Res. ,31, 155.
2. O’Keeffe, R.B., Fox, P.F. &Daly, C., 1976. Ir. J. Agric. Res. ,15, 151.
3. Kleter, G. &de Vries, Tj., 1974. Neth. Milk Dairy J. ,28, 212.
4. Visser, F.M.W., 1976. Neth. Milk Dairy J. ,30, 41.
5. Reiter, B., Sorokin, Y., Pickering, A. &Hall, A.J., 1969. J. Dairy Res. ,36, 65.