[1] Agr Res Ctr, Dept Anim Prod Qual, B-9090 Melle, Belgium
[2] Vet & Agrochem Res Ctr, B-1180 Brussels, Belgium
[3] European Commiss, Directorate Gen Hlth & Consumer Protect, B-1049 Brussels, Belgium
[4] State Univ Ghent, Fac Vet Med, B-9820 Merelbeke, Belgium