WALNUT – Contact with the horse’s body by the bark, the hull of the nut, or the wood will cause laminitis (founder) in the horse. The most common contact occurs from people using walnut shavings or sawdust as bedding. The shavings of walnut are dark in color and would be most often found in shavings from furniture factories.
MONENSIN – This substance is commercially known as Coban or Rumensin. This substance is a feed supplement commonly used for cattle and poultry. It is lethal in its pure form at the level of 1—2 mg/Kg of horse. Poultry feed with 100 g/ton or cattle feed premixes at 300 g/ton are lethal to the horse. Signs of poisoning include anorexia, profuse sweating, colic, stiffness, posterior paralysis, tachycardia, dyspnea (shortness of breath), hyperpnea (increased respiration rate), and uneasiness. Sublethal doses cause poor performance, unthrifty appearance, and often heart failure.
UREA – Another substance used as a feed supplement for ruminant animals. Urea has little feed value to the horse, but the horse can tolerate cattle feeds containing some urea without death. However, if the horse would ingest pure urea it would cause death.
MYCOTOXINS and MOLDS – Mycotoxins have become a problem with all animals, including horses. Currently it appears that three toxins are the major difficulty – aflatoxin, fusarium, and zeralone. Feed manufacturers currently test most commercial feed grains for aflatoxin. Using home or locally grown feed that has been improperly harvested or stored may cause problems. Under no conditions should feed with apparent mold be fed. Mold can be destroyed, but there is no practical method of removing the toxin. Mold toxins will cause liver damage, damage to the nervous system, and death. Molds grow rapidly with moisture over 16% and temperatures of 65º or higher. Sweet feeds can be a problem because of moisture and readily fermentable carbohydrate.
BLISTER BEETLES – This beetle has received much publicity due to several deaths caused by horses ingesting them. The blister beetle infests alfalfa fields that are in bloom. The beetles contain the irritant cantharidin, and if the beetle gets baled into the hay and then is ingested by the horse, excessive irritation to the digestive tract and death can occur. This beetle is about one inch in length, pure black or black with gray edges on the wings, or black with a red head or gray with a red head, or yellow brown with dark stripes, or gray. They have distinctive heads and long cylindrical bodies.
Blister beetles are not a common problem in hay raised in Ohio, but if hay is purchased from the west and southwest, it should be inspected to be sure it is free of the beetle. If the hay is only mowed, the beetles can leave during the drying process, but hay that is crushed as it is mowed will contain the dead and dangerous beetles. It would take about 50 dead beetles to be lethal to a horse.