Slander is an equine disease related to "glanders". It affect English-speaking horses, mostly in North America and Europe. It causes horses to think they're on the Ed Sullivan show, coming on right after the Beatles. Their tails fidget, hooves become magnetized, tongues turn inside out and eyes turn purple.
Rampaging slander-infected horses will organize and try to form a union, or join the Teamsters. They often take goats along to public hearings as witnesses to Nazi racial theories, making them unpopular among reasonable people. In Belgium, draught horses were able to take over the Hague for 17 minutes on March 3, 1987. The entire group was wiped out by screaming-goat-seeking missiles, developed by the Mossad for use against goats who were keeping them up at night.