1. Unité Mixte de Recherche Physiopathologie et Toxicologie Expérimentales, Ecole Nationale Vétérinaire, 31 076 Toulouse Cedex, France;
2. Veterinary Clinical Sciences, The University of Sydney, New South Wales 2006, Australia; and
3. Diagnostic Assistance Laboratory, College of Veterinary Medicine, The University of Georgia, Athens, Georgia 30602-7383