Reducing Your Horses’ Risk of Rapid and Unexplained Death

Learning to recognize potential risk and eliminating that risk is a proactive way to hopefully prevent a sad and avoidable death.

Choosing to live a life working with draft horses, as opposed to just dreaming about it, takes more than an active imagination. Photos by Vicki Schmidt.

Editor’s note: This article was originally published in the October 2010 issue.

There is no denying that working drafts, or any lifestyle that accommodates horses and livestock, is hard work. However, hard work (and its associated aches and pains) does not compare to the emotional pain when a beloved draft experiences a rapid or unexpected death.

There are a few natural occurrences, such as a lightning strike, that will kill a horse instantly. While not overly common, horses are also subject to brain hemorrhage, strokes and heart attacks. Along with these events are several environmental causes that will kill a horse within a few hours or a day.

Rapid and unexpected death on the farm is most common from ingesting or inhaling naturally occurring toxins associated with plants and molds or from bacteria such as botulism, which can also enter through a wound. Tetanus, another naturally occurring wound-entering bacteria, may harbor in a horse for weeks, but once symptoms are exhibited the chances of survival are slim, and the days to death are painful. Reducing the chance your horse will encounter these life-ending risks in the course of an average day begins with a critical look at your farms ancillary vegetation, as well as your routine feeding habits.


While the list of potential plants with toxins is long, few are consumed in quantities large enough to kill horses. However, some, such as fescue and nutsedge, can harbor fungus that causes abortions and unthrifty conditions. The three most common and toxic plants seen the northeastern United States include nightshade, ornamental yew and the fast growing and very common native red maple.

Ornamental yew

This plant is exceptionally toxic to horses, as well as cattle, sheep and goats. Horses are particularly attracted to yew and will quickly migrate to it if they escape from their fencing and into dooryards displaying this non-native landscaping plant. Sadly, death is often sudden and rarely does a horse survive more than three hours after ingestion. Many times, horses are found next to the yew bush or evidence of clippings.

Red maple

The toxins in native and ornamental red maple are only created in the wilted stage of the green leaf. Fresh leaves are safe, but access to their grazing is not advised due to the risk of broken branches creating browse in the wilted stage. Horses are borderline browsers and will often view broken tree branches, wind-blown twigs or storm residue as an inviting change of diet. It only takes a few wilted red maple leaves to kill an adult horse. Symptoms occur within a few days of ingestion, with death following a few days later. There is no known antidote and pastured horses are often found extremely sick, lying down and unable to rise.


This plant is found in ground along fringe type areas such as low woods, roadsides and fencerows. It is wide-ranged and is well- established from Nova Scotia to Minnesota, through the Midwest, and as far south as Texas and Florida. There are over 1,500 known varieties of nightshade, with bittersweet nightshade being the most common to New England. True to its name, this variety of nightshade is very bitter and though horses can develop a preference for bitter browse, many times horses will avoid it. If your horse is fond of dandelions, make mental note; this indicates your horse does not mind bitter snacks. Bittersweet nightshade has flowers that are small and deep purple or bluish purple. The flower stalk rises between the leaf nodes or opposite the leaves. The small round fruits turn red when mature and stay on the vines through most of the winter.

Molds and fungus

Molds and fungus are an issue to keep on the forefront when looking to reduce risk from your feeding program. Molds form under favorable conditions that include oxygen, high moisture, warm temperatures and low sunlight. Feeding hay in a manner that accumulates uneaten hay at the bottom of the pile creates an ideal environment for these toxins. Additionally, with on-farm or purchased feeds, contamination can occur in any stage of processing:

in the field, during transport or in storage. Aflatoxins and mycotoxins are byproducts of molds and fungus and are responsible for most of the more deadly aspects of this type of poisoning. Remember, too, that in the absence of any visible mold, aflatoxin and mycotoxins can still exist at levels that can easily and suddenly kill a horse.

Bacteria are another less obvious evil lurking to harm our horses. The two most common are botulism and tetanus. Fortunately, vaccines and best on-farm management practices can help to virtually eliminate death by either of these.


Horses have extreme sensitivity to botulism bacteria, and for this reason, it is often termed “the most perfect killer.” While rare, it affects horses of all ages and has a high mortality rate. Botulism is the most potent toxin known to mankind and a minute amount will easily kill a horse. It attacks swiftly and within 48 hours, horses are rarely able to rise. Horses contract botulism most commonly by ingesting contaminated feed—usually hay, silage or grain—that has been improperly made or stored. Small animals that are baled in hay, especially round bales, are well-known to contribute to botulism contamination.


While more common in other parts of the world, tetanus in horses is now rare in the U.S. due to an effective vaccine. Wounds are the entry point, and horses usually show clinical signs in 10 to 14 days, though the bacteria can harbor in the horse for up to six months. Tetanus is hard to detect and once it binds to a nerve, it cannot be removed. Muscle spasms from tetanus can break bones and suffocation from the spasms is often the cause of death. Antitoxins are available, but expensive, and only work on the toxins that are in the blood.

A few other tidbits of information concerning farm toxins and causes of rapid and unexplained death in horses:

  • Botulism is most often with farms that feed round bales or haylage.
  • Hayfields fertilized with poultry manure may pose more risk for botulism.
  • Test your forage for pH (acidity). Botulism bacteria are extremely pH-sensitive. Acidic levels below 4.5 are probably safe to feed.
  • Clean all wounds and encourage draining of deep ones to fend off tetanus and vaccinate annually.
  • Keep rusty items, farm equipment and other dangerous items out of your horses’ environment.
  • If feeding haylage or silage products vaccinate for Botulism, especially broodmares.

Rarely is a farm 100 percent safe from hazards and dangers that can cause irreversible harm to your horse. Learning to recognize potential risk and eliminating that risk is a proactive way to hopefully prevent a sad and avoidable death. Spend time researching online or engage the services of your local extension and farm service agencies to help learn how to recognize and eliminate toxin-producing hazards from your farm.