1. Maxwell H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, Kentucky, USA
2. Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA
3. University of Kentucky Veterinary Diagnostic Laboratory, Department of Veterinary Science, University of Kentucky, Lexington, Kentucky, USA
4. Department of Veterinary Clinical Medicine and Department of Comparative Biosciences, College of Veterinary Medicine, University of Illinois Urbana-Champaign, Urbana, Illinois, USA