1. Animal Science Department,Faculty of Agricultural and Food Sciences,American University of Beirut,850-3rd Ave.,New York,NY 10022,U.S.A.
2. United States Public Health Service,Centers for Disease Control,Atlanta,Georgia 30333,U.S.A.
3. Department of Diagnostic Medicine,College of Veterinary Medicine,University of Minnesota,St.Paul,MN,U.S.A.
4. SPARBOE Companies,Litchfield,Minnesota,U.S.A.