1. Animal Breeding and Genetics, Agricultural Research Council-Animal Production, Private Bag X2, Irene, 0062, South Africa.
2. Department of Animal, Wildlife and Grassland Sciences, University of the Free State, P.O. Box 339, Bloemfontein, 9300, South Africa.
3. Department of Animal and Wildlife Sciences, University of Pretoria, Private Bag, X20, Pretoria, 0028, South Africa.