First ascentionist Randy Leavitt on the name:
The Horse Latitudes were known to sailors as an area of light winds where sailing ships would be stuck for prolonged periods of time without the ability to move along their route. So long, in fact, that they would have to jettison their valuable horses, in order to save enough provisions for themselves. Subsequent sailors would come upon the bodies of dead, bloated horses floating about 30 degrees north and south of the equator. These became known as the Horse Latitudes. Jim Morrison of the Doors made a poem/song about this with riveting descriptions. It struck me as an appropriate name for a climb next to Planet Earth, where I was sure to be left stranded and unable to make progress for some time. It also paid tribute to the early days of sailing, which must have been one of the most exciting, yet demanding times in human history. 
1 recorded ascents.