[1] UNIV MARYLAND, DEPT ANIM SCI, COLLEGE PK, MD 20705 USA
[2] USDA ARS, IMMUNOL & DIS RESISTANCE LAB, BELTSVILLE, MD 20705 USA
[3] UNIV VERMONT, DEPT ANIM SCI & FOOD SCI, BURLINGTON, VT 05405 USA
[4] CORNELL UNIV, NEW YORK STATE COLL VET MED, ITHACA, NY 14850 USA
[5] UNIV MARYLAND, VIRGINIA MARYLAND REG COLL VET MED, COLLEGE PK, MD 20705 USA