[1] Colorado State Univ, Vet Teaching Hosp, Dept Clin Sci, Ft Collins, CO 80523 USA
[2] Colorado State Univ, Coll Vet Med, Equine Reprod Lab, Ft Collins, CO 80523 USA
[3] Colorado State Univ, Coll Vet Med, Dept Clin Sci, Ft Collins, CO 80523 USA
[4] Colorado State Univ, Microbiol Immunol & Pathol, Ft Collins, CO 80523 USA