Horses are more susceptible to injury and death from shock because of their physical makeup Horses and electricity do not mix Horses are more susceptible to injury and death from shock because of their physical makeup

THERE ARE many situations where electricity benefits horses. Equine fractures are healed more quickly using electrical bone stimulation. Scarring and bleeding are reduced through the use of electrocautery during surgery. Arrhythmias and other heart abnormalities sometimes are corrected through the use of electroshock or defibrillation.

TENS (Transcutaneous Electro Nerve Stimulator) units provide controlled electrical stimulus that can help horses in rehabilitation programs regain the use of damaged muscles, ligaments, and tendons. Even though electricity can be a helpful servant in these and other ways, more often than not, horses and electricity do not mix.

Not only are farms high-risk locations for electrical-related injuries to humans and livestock, but horses also are more highly sensitive to electrical damage. To understand why, we need to look at the physics of electricity and how it causes tissue damage.

How shock injuries occur

Several factors determine the nature and extent of electrical injury in humans and horses. The type of current being used is the first important piece of information. High-voltage direct current (DC) injuries are not common in horses because there are few sources of this type of electricity in their environment.

Batteries and generators are the principal types of DC that a horse might encounter. This type of electrical contact results in a strong and extremely rapid muscle spasm, often throwing the victim forcefully away from the current and resulting in blunt-force injury. Occasionally, short-circuited batteries in trailers or some electric fences can produce this type of injury, but the shock causes the horse rapidly and forcefully to back away from the source, and the injury usually is not severe.

Alternating current (AC) is the standard type of electricity found in power cords, electrical plugs, and most standard wiring in houses and barns. AC is three times more dangerous than DC of the same strength or voltage because muscle contracture occurs when a person or animal contacts AC even at low levels. This contracture then preserves the contact between the victim and the current, which leads to a longer duration of contact and greater electrical injury.

Since horses commonly chew on wiring or step on electrical cords, this contracture makes them unable to release a wire from their teeth or to move off a "live" power cord.

The amount of electricity needed to produce muscle contracture in humans is low. An electrical source producing one to two mA (milliamperes) of electricity will cause a tingling sensation, but a 200-pound human physically cannot let go of a wire carrying nine mA. Since this mA threshold depends on the size of the victim, one would think that horses could tolerate more voltage, but other factors contribute to making them even more sensitive.

Resistance is the tendency of a material to resist the flow of electrical current. Higher resistance tends to slow the passage of electricity through the body and increases the chance that the electrical energy will be changed to thermal energy, which causes the tissue to heat up and become damaged. Tissues in the body that are good conductors of electricity and consequently lower in resistance--nerves and blood vessels--tend to be less affected by low-level electrical contact. Dry skin and muscles are moderately resistant; tendons, ligaments, and bones are the most resistant.

Horses proportionally have more of the types of tissues that resist electricity. Their heavy muscles, thick tendons and ligaments, and large, bony skeleton make them especially sensitive even to low levels of current. Another factor that determines the severity of an electrical injury is the duration of the shock or contact with the current. Because horses are composed of a majority of tissues that slow down or resist the passage of electricity, they tend to be vulnerable to injuries caused by longer duration of contact, as well. Higher resistance and longer duration of exposure combine to be severely detrimental to the horse.

Mary Ann Cooper, M.D., of the University of Illinois at Chicago-based Lightning Injury Research Program, described why four-legged animals such as horses and cows are much more sensitive to electricity than are two-legged animals.

"The most disastrous individual electrical injury occurs when the person or animal becomes part of the electrical arch, since the temperature along the arch in a lightning strike can reach 2,500¡," she wrote.

Because a horse's front feet are a relatively long distance from its back feet in terms of the travel of electrical current, the horse's body usually becomes part of the arch of the current's path during a shock or lightning strike. Horses walking in an area with stray electrical ground voltage or horses exposed to "step voltage" (current spreading rapidly through the ground) are especially sensitive. Electricity enters one part of the body and travels through the body to exit at another.

The longer the distance between parts of the body, the greater the arch and the higher the temperature in the tissues. This high temperature causes massive tissue destruction throughout the body. Most deaths caused by electricity in horses occur before this tissue destruction comes into play, however, since most deaths are caused by short-circuiting of the body's electrical systems such as the heart, the respiratory center, or the nervous system. Cardiac arrest, respiratory arrest, and nerve instability are the rapid consequences of substantial electrical injury in the horse.

Another reason horses are more likely than humans to be injured fatally from electrical shock is what happens following the incident. Humans are much more likely to receive quick medical attention, whereas horses often are out at pasture during a storm without many people observing them. Injuries in barns, such as chewing through cords or wires, often are unobserved.

Rapid attention and cardiopulmonary resuscitation (CPR) often is successful in humans following electrical injury. This factor may be the most important reason why most horses struck by lightning die, while 70% of humans survive. CPR in the horse is difficult at best, and because many electrical injuries are unobserved, there is often no chance even to try.

Electrical safety

The problems with a horse's innate sensitivity to electrical current, its increased resistance that leads to a longer duration of contact, and its tendency to become part of the electrical arch make it imperative to practice electrical safety constantly around horses. Here are some tips for making your horse's (and your) environment safer:

• All wiring in barns should be in metal or heavy plastic conduit;
• Periodic inspections by a certified electrician should be done to ensure that worn or frayed wires are replaced, cracked conduit is repaired, and no short circuits or stray electrical impulses exist;
• Care should be taken not to overload circuits. It is common in the summer to see many fans plugged into one or more electrical outlet strips all running off of one circuit. This hazardous practice is repeated in the winter with lamps and other heating devices. Short circuits can occur and lead to direct shock injury or to step voltage as the electricity travels along a metal support, through wet floor surfaces, or elsewhere within the barn;
• Keep cords and wires away from areas where horses can chew on them. Stall boredom leads many horses, just like inquisitive children, into trouble;
• Inspect trailers and electric fence chargers for short circuits and faulty wiring;
• Look closely at all the electrical equipment you use that potentially can come into contact with your horse: clippers, vacuums, mechanical hot walkers, and water bucket heaters. The same is true for veterinarians. Ultrasound machines and power dental equipment should be inspected routinely and thoroughly; and
• Use extreme caution when walking horses around extension and power cords. Cords on asphalt or concrete are potentially deadly. A horse that steps on a cord on a hard ground surface easily can cut into the wires and instantly be electrocuted. Horses with shoes are even more likely to cut extension cords, so always keep these items off the ground or, if that is not possible, run cords through sections of PVC pipe or between two boards to keep horses from stepping directly on them.

Lightning

Lightning injuries are a special category because they are harder to predict or prevent but tend to be more dramatic and sensational. Human lightning deaths vary from 50 to 300 per year, depending on weather patterns, with four to five times as many nonfatal injuries yearly. Many equine lightning deaths are not reported, so exact statistics are not available. But, since more horses than humans routinely are exposed to the elements and horses are more electrically sensitive than humans, the actual numbers are probably higher.

Horses tend to seek shelter during storms by grouping together and standing under trees, which puts them even more at risk. Horses standing near water troughs, along fence lines, and in low-lying areas containing standing water also are at increased risk for step-voltage lightning injury.

While it is often impossible to protect pasture horses from passing storms and lightning, well-placed run-in sheds in areas that do not collect standing water may help. Horses at pasture that do not require shoes should go barefoot since this may lessen their risk, as well.

Electricity does so much to make our lives easier that we tend to take it for granted and forget that it just as easily can hurt. Horses have many reasons to be especially sensitive to electrical injury, so prevention and barn safety are always necessary since there are no second chances.