Dr. Temple Grandin
Dr. Temple Grandin
(photo: Rosalie Winard)

KANSAS CITY, Mo. – The Humane Slaughter Act requires that animals be rendered insensible to pain by a single blow or gunshot or an electrical, chemical or other method that is rapid and effective. The requirement is that the animal is not able to feel pain after stunning. Recent research using electroencephalography (EEG) brain waves indicates there are definite indicators when an animal is fully sensible and able to feel pain and other indicators that it is unconscious and brain dead.

A review of the literature of studies conducted in slaughter plants supports the concept of a transition zone between consciousness and unconsciousness (Terlouw et al., 2016ab). This is especially true when animals are bled without stunning (Verhoeven et al., 2016a). EEG studies show that a corneal reflex in response to touching the surface of the eyeball can occur in unconscious animals (Verhoeven et al., 2016c). To clarify assessment of unconsciousness and consciousness it is recommended to separate the signs of a definitely conscious animal from signs of unconsciousness or death. Any one of the following six indicators is a sign that the animal is definitely conscious (Terlouw et al., 2016b):

• Standing posture
• Head or body righting reflex
• Voluntary vocalization
• Spontaneous blinking (no touching). Do not confuse with nystagmus (vibrating eye).
• Eye pursuit
• Response to threat or menace test (no touching). Hand waved in front of the eye. Do not confuse with nystagmus.

To ensure an animal is unconscious and brain dead, before carcass disposal or invasive dressing procedures at a slaughter plant, all three of the following indicators must be absent: (Only when all three of these indicators are absent is the animal definitely unconscious.)

• Absence of corneal reflex (touch the eyeball surface)
• Absence of eyelash reflex (response to touch)
• Absence of rhythmic breathing (Terlouw et al., 2016b)

The animal is in the “transition zone” between consciousness and unconscious if one or more of the following signs is present:

• Eyelash reflex (response of eyelash to touch)
• Rhythmic breathing (Terlouw et al., 2016ab)
• Corneal reflex

If any of these indicators are apparent, re-stun the animal immediately. Rapid re-stunning will prevent return to consciousness and prevent a violation of the Humane Slaughter Act.

On large animals, such as cattle, the corneal reflex can be assessed by using a finger to touch the eyeball. On small animals, such as pigs or sheep, do not use a finger to assess the corneal reflex. Poking with a finger may push the eyelid shut and cause it to get glued shut with mucous. When the mucous loosens, the eye may suddenly pop open and be misinterpreted as a blink. Use the tip of a pen or other small blunt object to touch the surface of the eye of pigs, sheep, and other small animals. Spontaneous blinking or response to the menace reflex must have the full cycle of opening and closing of the eye. It should look like natural blinking of a live animal in the lairage.