Oleander is a woody shrub seen mostly in southern and western areas of North America. it's a pretty flowering shrub, and some people keep it as a potted houseplant. But it doesn't belong on a horse farm. The potency of this toxic plant was evidenced in the February 15 issue of the Journal of the American Veterinary Medical Association.
Researchers at the veterinary college at the University of California at Davis did a retrospective study looking back at cases of oleander poisoning in 30 horses at the clinic there. Fifty percent of the horses died, with three dying as they arrived at the clinic or shortly thereafter. Clearly, a serious toxin.
Signs seen with horses with oleander poisoning include colic, possibly with diarrhea as well, and kidney damage. The crucial problem however is changes to heart rhythms. Cardiac symptoms were the most common cause of death. The horses who did survive had extended hospital stays with intensive care given.
The scariest part was that many of the horse owners were either unaware of any oleander on their property or felt there was no way the horse could have possibly eaten any oleander. Some of the horses had been moved to new grazing areas and three of the horses had escaped and been loose for a period of time.
BOTTOM LINE. If you live in an area where oleander can thrive outdoors, check your property thoroughly. Twenty leaves of oleander are enough to kill a horse. Before moving your horse to a new pasture, walk it completely to rule out any oleander?or any other toxic plants. We recommend you become familiar with the Cornell Poisonous Plants database at http://www.ansci.cornell.edu/plants/. Toxic plants from all over are covered there, not just native New York plants. You can also visit http://plants.usda.gov/java/ and look up plants. They generally have excellent photos, too.
Deb M. Eldredge, DVM, Contributing Veterinary Editor