In recent years authorities have tightened restrictions on the disposal of equine carcasses euthanized with the barbiturate pentobarbital. Concerns include groundwater contamination, soil contamination, pet food contamination at rendering facilities, and poisoning of scavenging wildlife or domestic animals. Consequently, veterinarians need alternative options for euthanizing horses.

J.R. Lund, DVM, MS, Dipl. ACVPM, ACVR, diagnostic animal radiologist at the University of Wisconsin School of Veterinary Medicine, in Madison, and a team recently assessed the safety and efficacy of gunshot euthanasia. She presented their findings at the 2020 American Association of Equine Practitioners’ Convention, held virtually.

The Study

The American Veterinary Medical Association lists gunshot as one of its acceptable euthanasia methods, so long as the veterinarian uses proper anatomic site, firearm caliber, and bullet type.

“While gunshot euthanasia has been used for countless years, there is currently limited published research” on its use, said Lund. “The aim of our study was to evaluate with computed tomography (CT scan) the characteristics of brain tissue disruption and skull damage in cadaver heads of adult horses caused by six firearm-ammunition combinations applied at a novel anatomic aiming point.”

Her team used 53 cadaver heads randomly sorted into different firearm, ammunition, and position groups. The firearm-ammunition combinations they evaluated included:

1. Semi-automatic 9mm pistol with 147-grain jacketed hollow point ammunition;
2. Semi-automatic .45-caliber ACP with 45-caliber 230-grain jacketed hollow point ammunition;
3. Semi-automatic .223-caliber carbine with .223-caliber 55-grain jacketed hollow point ammunition;
4. 12-gauge shotgun with a 1-ounce slug;
5. .22-caliber long rifle pistol with .22-caliber 40-grain plated lead solid core ammunition; and
6. .22-caliber long rifle pistol with .22-caliber 40-grain plated lead hollow point ammunition.

“As law enforcement may be in a position to euthanize horses by gunshot, we felt it was important to include firearms that were commonly available to them (1-4) along with firearms that are more commonly owned by the public (5-6),” said Lund.

She explained that they chose a reliable and palpable aiming point where the two temporalis muscles at the front of the horse’s forehead form an inverted V.

“Having a palpable landmark was helpful, while also ensuring that we were high enough to avoid entering the sinuses,” Lund said. “We did review some anatomic references and determined that an approximate entry angle of 70 degrees would be appropriate.”

They performed gunshots in simulated standing and lateral recumbency (lying on one’s side) positions, then took CT scans of the cadaver heads to assess and score damage to the cerebrum, cerebellum, brainstem, and spinal cord.

Lund said the .22 long rifle pistol with hollow point ammunition tended to score the lowest (causing the least amount of damage) while the .223 and the shotgun had the highest scores (most damage). She said the shotgun, in particular, caused a tremendous amount of damage.

While this makes it “devastatingly effective,” it does risk overpenetrating the skull, “which can put an increased risk on the personnel in the vicinity during a gunshot euthanasia using this combination,” said Lund. “I do think this is a concern worth noting.”

The other firearm damage scores did not differ significantly, and all were effective. Lund said her team’s personal preference when performing gunshot euthanasia is the 9mm.

“The 9mm pistol is a handgun and is easier to maneuver compared to long-barreled firearms such as the shotgun,” she explained. “A handgun can also be holstered before and after euthanasia, thereby allowing the firearm operator the opportunity to secure the firearm quickly and safely.”

Take-Home Message

Lund said a firearm operator’s familiarity with the firearm-ammunition combination and identification of the correct anatomic aiming point are critical for a successful gunshot euthanasia outcome with the least potential risk to the animal handler, the firearm operator, and the anyone standing nearby.

“Our results indicated that the examined firearm-ammunition combinations, when applied to the novel aiming point, appeared to be a reasonable alternative for equine field euthanasia,” she said, when pentobarbital is not an option.