MSU Extension Pork

As the most common and acceptable methods (AVMA and AASV) of euthanasia used on swine farms for grower pigs and breeding stock are firearms (rifles and shotguns) the following discussion on firearms is in alignment with this issue of the Pork Quarterly’s focus on farm safety. Co-author, Steven Howard, is a third-generation gunsmith and recognized firearms expert in 14 state and federal courts.

Overview: A basic knowledge of firearms and the ammunition is necessary to interpret both euthanasia and human safety. The following discussion will be limited to these methodologies. In the subsequent issues of Pork Quarterly, we will compare use of firearms and captive bolt for humane swine euthanasia.

1. Firearms:

Rifles: Have spiraled grooves (rifling) cut the length of the inside of the barrel. The purpose of rifling is to cause a rotational spine to the bullet on the longitudinal axis stabilizing a bullet’s flight. The caliber of a weapon, is determined by the diameter of the gun’s bore such as .22 (inches). Rifles are shot from the handler’s shoulder and used for longer distances and precision. Projectiles (ammunition) reach speeds of 762 to 1160 m/s¹. It is considered that rifles are the best tool for their low cost, efficiencies and ability to humanely euthanize even a larger pig.

Shotgun: Is a firearm with a smooth or rifled barrel and are fired from the shoulder dispersing shots (pellets, buck shot and slugs) at shorter distances.  Velocities range from 366-396 m/s, with pellets a slower velocity than slugs. Slugs are used commonly for deer and bear hunting in highly populated areas as with the intention to reduce long range shooting accidents.

2. Ammunition:

Ammunition cartridge is comprised a cartridge case, a primer, propellant and bullet (projectile). Rifle bullets consist of either a metal jacket or led. There are full metal jacket bullets, half metal jackets, and partial metal jackets. Full metal jackets are typically used for high velocity firearms, used in the military or while hunting wild game and should not be used in on-farm situations were pigs can be restrained and euthanized individually.

Shotgun cartridge (shells) are composed of a cartridge case of plastic or cardboard, a primer in the base, gunpowder, and the wadding and shot enclosed in the casing. Shell sizes are based on length and gauge. The gauge refers to the caliber size referring to the number of lead balls that can make up a pound. Because shotguns throw out either a very large single slug, or many smaller balls they are not a particularly useful or safe tool to use in a farm euthanasia environment. Each projectile has the possibility of ricochet and causing the secondary casualty.

Firing a firearm:

Pulling the trigger, the firing pin is released and the pin strikes the primer, crushing and igniting it. The metal cartridge case expands and isolates the chamber of the weapon against a backward escape of gases when fired. The primer (center fire or rim fire) is ignited and produces an intense flame through a flash hole. The flame flows though the flash hole and ignites the powder in the cartridge producing a large quantity of gas and heat. This heat and pressure expels the projectile (bullet) through the barrel. As the bullet emerges it is accompanied by a jet of flame and gas.

A General Rule: One gram of propellant produces 1 liter of gas under high temperature and pressure¹.

Ballistics is the science of projectile travel and is expressed in a common formula describing the influences of mass of the bullet and muzzle velocity on the amount of Kinetic Energy (KE) that can be delivered to a target or tissues by a projectile. If mass of the bullet is doubled then KE on the target is doubled. However, if muzzle velocity is doubled, then KE is quadrupled. Velocity is determined by the type of firearm, distance traveled and type or changes of media in the path²

Kinetic energy (foot pound) = ½ Mass * Velocity.

Four Rules of Firearm Safety (taught in all police academies). ⁸

1. Always treat every firearm as if it is loaded.
2. Always keep muzzle pointed in a safe direction.
3. Keep your finger outside the trigger guard until you are ready to shoot.
4. Always be sure of your target and what is in front and behind it.

 3.  How tissue damage occurs:

Tissue damage can occur in three ways: 1. laceration or crushing; 2. cavitation and 3. shock waves. Laceration, affected by the characteristic of the ammunition, forms a wound cavity, where the crush and stretch forces act on the tissues. Thicker tissue such as brain and cortical bone (skull) offer great resistance, increasing the energy transfer or KE from the projectile to the tissue. In addition, cortical bone tends to fracture and fragment ideally causing more disruption of the brain. Secondary fractures of the skull occur due to the gas produced from the weapon which enters the cranial cavity and expands intracranial pressure. Therefore, euthanasia of the pig occurs when the correct amount of energy is used for the size of the animal, the additional fragmentation of bone on the brain and the disruption from the brain stem due to the shock waves.

4. The science of Ricochet:

Jed Clampett hustles the pool hustler at the “billy-ard" table saying “this is just like ricochet shootin”.

Although bullets and shotgun pellets lose energy after string a surface, they retain sufficient energy after ricochet to inflict serious or fatal injuries³. A national database for entry of these types of accidents on humans does not exist. There is both anecdotal evidence from other veterinarians or through conversations with farmers and forensic investigation have described individual cases to emphasize a point. 

Also, solid point bullets can begin to penetrate but, depending on energy transfer and bullet quality, part of the bullet shears off and follows a separate trajectory⁵.  In other situations, the bullet may fragment on impact causing fragments to spray out in a fan. Further, the surface itself might fragment, sending secondary projectiles injuries. 

The shape of the bullet determines whether it will ricochet. Round noses bullets are more likely to ricochet than flat-nosed bullets and full metal jacket bullets are as likely as lead or lead alloy bullets. At short distances, hollow point or low-velocity bullets (ie shotgun) are less likely to ricochet, when compared to flat-nosed, lead or high-velocity bullets³.  In addition, the soft-point ammunition deforms or mushrooms when entering the skull and destroys brain tissue more effectively. However, if a hollow-point bullet ricochets, it might fail to expand and penetrate more deeply than the direct shots. If animals are required to be shot from a distance, a high-velocity bullet should be used¹.

Interestingly, projectiles at low velocity are also more likely to ricochet than high velocity projectiles. As mentioned earlier (KE = 1/2 * velocity) the kinetic energy determines the penetration of the bullet to the target. Research⁴ have demonstrated a “billiard ball” effect when the leading pellets in the shot decelerate at the point of impact, as the pellets in the rear overtake the lead pellets and collide with them causing the shot string to scatter. When shotgun pellets ricochet, the pellets will spread out horizontally. For shotguns, the steeper the angle of incidence, the wider the spread of shot. Consider when the average height person aims the muzzle down toward the skull of a pig, the angle of incidence is near 45-60 degrees. With many barns having open curtain siding, this information further confirms that small children, pets and people should not be in the barn area within at least 60 yards when a rifle or shotgun is fired.

Wounds: When bullets ricochet, they may tumble and strike an unintended target in an unstable condition. This effect can cause larger and more irregular wound shape and tend to penetrate rather than perforate⁶.

 Advantages of firearms:

• Experienced operators can achieve a humane pig euthanasia, safely.
• Firearms and ammunition are readily available.
• High velocity ammunition of a small caliber is humanely effective.⁷

Disadvantages of firearms:

• Potentially the most dangerous of humane euthanasia of swine.
• The potential for ricochet.

Humane Swine Euthanasia using Firearms:

Humanely swine euthanasia can be completed from close range using a .22 caliber rifle with long-rifle mushroom shells such as a hollow point or a soft-shell lead.

The procedure should be performed outdoors whenever possible and in a location away from public access. The trajectory of a ricochet bullet is impossible to predict. People, other than the shooter, should be cleared from the area. Assistants should stand behind the shooter.

To improve euthanasia - the distance from the muzzle to the skull target should be 2-6 inches.

The barrel of the firearm should never be placed directly against the animal’s skull.

As a properly euthanized animal will undergoes tonic/clonic actions, improve shooter safety by restraining the pig using a rope snare secured to a solid object.

• Contributors: The authors thank by Nancy Bradley-Siemens, DVM, Clinical Assistant Professor, Midwestern University, AZ and D. James McGuire for their contributions and content review.