[1] ARS, USDA, So Plains Agr Res Ctr, College Stn, TX 77845 USA
[2] Texas Agr Exptl Stn, Dept Vet & Poultry Sci, College Stn, TX 77843 USA
[3] Food Safety Inspect Serv, USDA, Emerging Pathogens & Zoonot Dis Div, Washington, DC 20005 USA
[4] Mississippi State Univ, Coll Vet Med, Mississippi State, MS 39762 USA