1. The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Edinburgh EH25 9RG, UK
2. Centre for Tropical Livestock Genetics and Health (CTLGH), Roslin Institute, University of Edinburgh, Edinburgh EH25 9RG, UK
3. Department of Animal Science, University of California Davis, Davis, CA 95616, USA
4. Department of Animal Science, Texas A&M University, College Station, TX 77843, USA
5. Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, Uppsala 750 07, Sweden