The Authors have adhered to the Principles of the Veterinary Medical Ethics of the AVMA.
Conflict of Interest The Authors declare no conflicts of interest.
Funding Sources
This project was supported by the Center for Equine Health with funds provided by the State of Califor- nia Pari-Mutuel Fund and contributions by private donors. A Short Stay PhD Fellowship granted by Utrecht University was used to fund travel and housing expenses for the first author to perform the practical work at UC Davis.