Lightning, which is electrical energy measured in the millions of volts, can strike livestock dead in less than a second.
But even exposure to a few stray volts can significantly affect an animal’s behaviour.
Stray voltage is the electrical voltage measured between two points when they are touched at the same time to complete a circuit. Although a person is unlikely to sense this low level voltage, animals readily perceive it as it flows through their bodies.
Exposure to stray voltage can cause cows to avoid areas or objects. This can hurt production, especially if metal feeders or waterers are involved. A dairy cow may refuse to walk into the milking parlour when she senses this minute electrical energy. If an improperly grounded milking machine generates stray voltage on a cow’s udder, it may fail to let the milk down.
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Stray voltage can arise from a variety of sources including poorly installed electric fences, wiring systems that do not meet standards, ground faults or shorts, undersized wiring, loose or corroded connections, moisture, or wiring damaged by animals.
A crude way of testing for stray voltage is to put one hand on a piece of metal equipment and the other hand on a wet concrete surface. If you feel a tingling sensation, you are picking up stray voltage. This will not work if you are wearing rubber boots that insulate you from the ground.
Stray voltage can also be measured with a meter. Readings between waterers or other metal objects and surrounding ground should be taken at several sites.
Stray voltage can sometimes be detected just by observing cattle closely. Do they look like they are trying to avoid particular metal objects? Do they refuse to drink from certain waterers or eat from specific feed bunks?
Though animals are more sensitive than people to stray voltage, there is also a difference between species – pigs are more perceptive to this electrical force than cattle.
A meagre flow of 0.5 volts is detected by less than one in 50 cattle. At two volts, most cattle showed some subtle behaviour changes. In one study, four out of 30 animals tested refused to drink from a metal waterer when the voltage was greater than five volts. Because the majority of the group still drank from the waterer, the avoidance behaviour in the remainder of the herd could easily have been missed if the animals had not been under close observation.
If a stray voltage problem is identified, an electrician should be called in to examine and repair the system. Stray voltage caused by 240-volt systems is usually the responsibility of the utility company.
A lightning discharge involves exposure to electrical energy just like stray voltage. However, it can have catastrophic consequences. Luckily, lightning strikes occur only in certain seasons and are isolated events.
On pasture, lightning typically strikes tall trees with large, spreading root systems. If the ground is wet, has tile drains or standing water, the discharge can electrify the entire field not just the tree.
An animal hit by lightning usually dies from cardiac arrest. The current passing through its heart causes fibrillation, which is an unco-ordinated muscle activity that fails to pump blood. Lightning can also halt respiration. In either case, death is instantaneous.
If lightning is suspected in a death, there should be evidence of a strike close to where the animal died. Trees may be burnt, fence posts split, or the wire on the fence welded. The dead animal may have burn marks on its legs.
Jeff Grognet is a veterinarian and writer practising in Qualicum Beach, B.C.
