1. Teagasc, Animal and Grassland Research and Innovation Centre; Grange, Dunsany, Co.; Meath Ireland
2. UCD School of Agriculture; Food Science and Veterinary Medicine, Univ. College Dublin; Belfield Dublin 4 Ireland
3. Swedish Univ. of Agricultural Sciences; P.O. Box 7043, SE-050 07 Uppsala Sweden
4. Bioforsk; Norwegian Institute for Agricultural and Environmental Research; Kvithamar, N-7500 Stjørdal Norway