1. Department of Animal Sciences, University of Stellenbosch, Matieland 7602, South Africa
2. Institute for Animal Production: Elsenburg, Private Bag X1, Elsenburg 7607, South Africa
3. Institute for Animal Production: Oudtshoorn, PO Box 351, Oudtshoorn 6220, South Africa
4. SARDI, Livestock and Farming Systems, Davies Building, Roseworthy Campus, Roseworthy, South Australia 5371
5. School of Animal Biology M085, Faculty of Natural and Agricultural Sciences, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
6. UWA Institute of Agriculture, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia