Although horses were traditionally shot when badly injured, it is becoming more common for vets to inject a barbiturate overdose. However, in some situations it can be dangerous to attempt an injection. If the horse is in shock, its circulation may be too impaired to transport the drug to the brain and heart, and the veins may be difficult to locate. The veterinarian may need to use a .22-caliber pistol to euthanize the animal. If the gun is properly positioned, death should be instantaneous.