By Tony Buffington, DVM, PhD
The Fear Free movement aims to minimize the fear pets feel in our care, whether it happens in veterinary practices, shelters, or homes. Sometimes we need to restrain or immobilize animals for care, so we need to understand the effects of restraint from the animal’s point of view.
Some might be surprised to learn that the effects of restraint and immobilization of animals have been studied for hundreds, probably thousands of years. Animals become immobile naturally for a few different reasons. For example, immobility is a natural part of animal defense responses in the presence of a perceived threat. This “defense cascade” begins with arousal (orientation toward the threat). If not disrupted it continues through freezing and flight or fight to tonic immobility (TI) in the presence of an inescapable threat (Table 1). This response is well known in nature and can be triggered by our restraint efforts, however well intentioned.
In addition to the defense cascade, we see other kinds of immobility in some animals, including the immobility of ambush predators when hunting, the immobility of their prey when being hunted, and dorsal immobility (Table 1). Dorsal immobility results from application of pressure to the skin, usually the nape of the neck or along the back, and occurs in young animals when carried by their mother, in queens when held by tomcats during sex, and when clips are applied to some animals (“clipnosis”).
Although dorsal immobility is qualitatively different from TI–it is not part of the defense cascade–any method of restraint can activate the defense cascade in a given animal. The challenge for Fear Free practitioners is to understand the defense cascade, recognize where in the cascade each animal is at any given instant, and know how to respond appropriately in the animal’s best interest.
While we are relatively familiar with the freeze, flight, and fight portions of the defense cascade, TI may be less familiar. Clinically, animals in TI stop moving (it is sometimes called faking death), their heart and respiration rates and temperature decline, they may defecate, and they may develop life-threatening arrhythmias.
Tonic immobility seems to occur less commonly in predator species (e.g., cats and dogs, although I did observe fatal tonic immobility in a cat once, and it can certainly occur in human beings1) than in prey species (such as rabbits, rodents, guinea pigs, and some birds), but the risk, while small, can be fatal for the animal, and has the potential to occur in any animal subjected to any given form of restraint, be it manual, “burrito,” “clipnosis,” a thundershirt, or other means.
How do we treat TI? By constant vigilance for its occurrence when we restrain animals (particularly prey species). If the animal suddenly goes limp, it may have relaxed, or it may have fallen into tonic immobility. If the response is accompanied by decreased heart and respiration rate or defecation, and especially if an arrhythmia is heard, the animal should be immediately released from the restraint, moved to a safe, quiet place, and observed carefully until returning to more normal behavior.
Animals who experience TI are likely to avoid the place where it occurred, just as animals do after flight or fight. After such an occurrence, the pet may need variable combinations of desensitization and counterconditioning, chemical restraint and home care to return their perception of safety and trust in caregivers.
This article was reviewed/edited by board-certified veterinary behaviorist Dr. Kenneth Martin and/or veterinary technician specialist in behavior Debbie Martin, LVT.