All trees of the prunus variety are toxic to some degree, although most frequently mentioned is the chokecherry. Cherry leaves, especially if the tree has been stressed (wilted, frost, etc.) concentrate a form of cyanide in the leaves and are very toxic to livestock.
Young cherry sprouts are thought to be toxic and/or to cause equine abortion, and even the bark of cherry trees is mentioned in several online articles as containing a lesser amount of some form of toxic cyanide. Most of the time horses and other livestock tend to avoid toxic plants, but the danger remains.
> Actually, wild black cherry leaves
> can be very toxic to all classes
> of livestock when they are wilted.
> Arsenic builds up and will cause
> certain death in livestock.