作者单位:Oklahoma State Univ, Dept Anim & Food Sci, Stillwater, OK 74078 USA[1]Michigan State Univ, Dept Anim Sci, E Lansing, MI 48824 USA[2]Michigan State Univ, Coll Vet Med, Pathobiol & Diagnost Invest, E Lansing, MI 48824 USA[3]Michigan State Univ, Large Anim Clin Sci, E Lansing, MI 48824 USA[4]