Lightning strikes

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Lightning Strikes

Horses are at risk of getting struck by lightning when they are outside in the pasture during thunderstorms. Hundreds of livestock are killed annually by lightning worldwide, with many incidents never reported. The degree of risk is dependent on:
  • The lightning flash or stroke density of the geographical area
  • Topographical landscape
  • Characteristics and distribution of trees (height, size, species, location relative to other trees, ground root system)
  • Habits of animals during storms
Geographical Area
Horses living in regions with high flash or stroke densities are more likely to get struck by lightning then those that aren't.
In the United States, these areas predominately include the southeast (especially Florida), Gulf States, the Mississippi and Ohio River Valleys, the Front Range of the Rocky Mountains, and some other mountains in the Desert Southwest.

Layout of the Pasture
Lightning is caused by an imbalance of positive and negative charges in the atmosphere. During a storm, negative charges are generated along the bottoms of clouds. Positive charges are generated on buildings, trees, or any objects that protrude upwards from ground level. As both these charges increase, once they reach high enough levels, it causes a streamer of negative charges to move erratically in the direction of the earth. At the same time, a short leader of positive charges may move a short distance upwards into the air. Once the two charges meet, the negatively charged streamer from the clouds completes its grounding path as the positive charges move upwards along the same path, and into the clouds. Any trees, buildings, or other objects that are tall and isolated, tend to generate more positive charges. Therefore, pastures that are hilly, contain isolated tall trees, buildings or other objects, are more at risk of getting struck by lightning.

The taller and more isolated the tree, the more it's at risk of getting struck by lightning. Also, certain trees are more susceptible to lightning strikes than others. These trees should be identified and either protected or removed from pastures where horses are turned out into.

Susceptibility of non-protected temperate zone trees to lightning strikes
Tree genusCommon NameSusceptibility to lightning strikes
LiriodendronTulip poplarVery High
RobiniaBlack locustHigh

Source: T Smiley, 2011

Animal Habits during Thunderstorms
The most common ways horses die from lightning strikes are not actually through a direct hit (direct strikes), but through indirect hits, which include:
  • Ground current: Ground current strikes occur when lightning hits the ground, causing the current (often 20,000+ amperes worth) to spread out along soil surface, including any obstacles (such as horses) that may be in the vicinity.
    Lightning Strike Radius
    For a horse standing on the ground affected by the current, it can travel up a hind legs, through their entire body and down the front legs. Along the way, it can potentially stop the horse's heart or arrest it's breathing. The greater the space between where the current enters the horse's body and where it leaves, the greater the potential for serious damage.
  • Side flash: Side flash occurs because lightning follows the path with the least resistance to electrical current to the ground. If a horse is standing underneath a tree that is struck by lightning, the lightning is more likely to jump from the tree to the horse. So one lightning strike to a tree or a strike to the ground can jump back and forth among all the animals nearby.
  • Contact strike: Occurs when a horse is touching an object that is in the pathway of the lightning current, such as if it hits a water trough or electric fence.
Summary of Reported Horse Deaths Caused by Lightning Strikes
3MIside flash; in pasture underneath treeAug-13unknown
12ALBarn was stroke by lightning and caught fireJan-14unknown
2WIwhile riding - side flash or groundJul-13unknown!baVYSC
2COside flash; in pasture underneath treeSep-13unknown
1PAside flash; in pasture underneath treeSep-13unknown
3canadaside flash; in pasture underneath treeSep-13unknown
2MOside flash; in pasture underneath treeJul-13unknown
2ALBarn was stroke by lightning and caught fireSep-13unknown
3canadaside flash; in pasture underneath treeSep-13unknown
1WYside flash; in pasture underneath treeSep-13unknown
1FLBarn was stroke by lightning and caught fireApr-13unknown
35GABarn was stroke by lightning and caught fireJun-13unknown
1MSgirl ridingJul-144:30pm
4MSpasture underneath treeJul-15unknown
3NCpasture underneath treeJun-15afternoon
0NChit barn and caused fireJun-156:00 PM
2MOdirect hitJul-1512pm
3PAstanding underneath a tree while out in pastureJun-15unknown
1Southwest FloridaStanding underneath a large oak treeAug-16early evening
1MIMan and a horse were killed horseback riding outside a barnApr-16unknown
2OHWoman was bringing in horsesAug-16unknown
1FLRace horse Brillant Speed was found dead in his paddock after a thunderstorm hitJul-16unknown
1AZHorseback riding, while heading home as storm was moving in; the horse was killed but than man survived.May-16unknown
1Mills River, NCLightning struck a large tree about 50 feet away from the horse trailer. The bolt traveled across the ground to the horses, killing one and injurying several others that were in a horse trailer hooked up to a truck.Jul-162:00 PM
1GALightning hit a tree that horses' were standing nearbyAug-16unknown
0MDLightning struck a horse barn that caught fireJul-165:00 PM
2UKHorses were out in the pasture and found dead in the fieldJul-163:00 AM
2Iowaman and horse he was riding were killed by lightning strikeMay-15evening


Found dead in the pasture after a storm
Abnormal behavior
Appears to be blind
Mouth twitching
Bleeding from the nose
Unable to stand


  • History
  • Clinical signs
  • Physical exam
  • Necropsy



Supportive care


  • Removal of isolated trees from pastures
  • Protection of isolated trees or horse shelters with a lightning protection system installed by a professional who knows what they are doing
  • Bring horses into barns protected with a lightning protection system when the weather forecast calls for thunderstorms
  • Any electrical fences installed should be grounded and its electrical continuity should be broken by insulation material in brakes in the wires at particular calculated intervals per manufacturers recommendation.



Scientific Research

General Overviews

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Risk Factors

  • Living in areas with a high lighting strike density (ie, Southeastern United States)
  • Lack of shelter in pasture
  • Isolated trees