Can horses go on passenger planes?

Yes, they can go on passenger planes. There are special passengers that can carry both passengers and cargo at the same. KLM Royal Dutch Airlines operates the 747-400 combi, an aircraft that is capable of carrying both cargo and passengers at the same time. The horses will be carried inside the cargo hold and will be pressurised similar to the passenger compartments.

Normally a chartered specialised cargo plane would do its job, but due to the special attention needed for the horses, it will be done via the Combi aircraft.