Finisterre Series by C.J. Cherryh

Rider at the Gate (Nighthorse, Book 1)Stranded on a distant planet that abounds with fertile farmland, human colonists appear to be in paradise. But all the native animals communicate by telepathy, projecting images that drive humans mad. Only Nighthorses stand between civilization and madness. When a flare of human emotion spreads to all the horses, chaos erupts.

On a distant planet, all the native creatures communicate telepathically, projecting images which drive humans to madness. As a result, the people live in walled cities and owe their lives to the nighthorses, equines who can bond with certain riders and provide a telepathic "buffer"... moreOn a distant planet, all the native creatures communicate telepathically, projecting images which drive humans to madness. As a result, the people live in walled cities and owe their lives to the nighthorses, equines who can bond with certain riders and provide a telepathic "buffer". But one savage winter, young Danny Fisher and his nighthorse Cloud lead the survivors of a deadly telepathic attack to shelter high in the snowbound mountains--only to discover their "sanctuary" threatened by a vicious predator never before known to humans. Sequel to "Rider at the Gate". less