1. Department of Animal and Dairy Science, University of Georgia, Athens, GA 30602, USA.
2. Animal Genomics and Improvement Laboratory, Agricultural Research Service, USDA, Beltsville, MD, USA.
3. Council on Dairy Cattle Breeding, Bowie, MD 20716, USA.
4. INRA, UMR1388 GenPhySE, Castanet-Tolosan, France.