[1] CIT, F-27000 Evreux, France
[2] Royal Vet & Agr Univ, Dept Anim Sci & Anim Hlth, DK-1870 Frederiksberg C, Denmark
[3] Univ Gottingen, Inst Anim Husb & Genet, D-37075 Gottingen, Germany
[4] Univ Edinburgh, Div Dev Biol, Roslin Inst, Roslin EH25 9PZ, Midlothian, Scotland