When it comes to handling rabbits, there’s a huge controversy surrounding one main action: Cradling rabbits on their back.
Some think this induces a major stress response, while others view it as a part of routine handling.
But, what do the experts have to say about it?
Tonic Immobility: What is it?
Tonic Immobility (TI) is a reversible, innate behavior characterized by temporary inhibition of motor functions (also typically referred to as akinesis, thanatosis, apparent death, and paralysis).
Symptoms of TI include stillness, unnatural body position, lack of reaction to external stimuli, tachycardia/bradycardia, decrease in respiratory rate and body temperature, and changes in EEG.
While rabbits are one of the most commonly thought-of species with the potential to experience TI, the condition is also noted in guinea pigs, mice, crustaceans, chickens, turtles, and sharks, among other animal species.
The Latest Study (2021)
In “Effect of tonic immobility induction on selected physiological parameters in Oryctolagus cuniculus f. Domesticus rabbit” (Wilczyńska et al), a group of researchers wanted to determine how gently-induced tonic immobility would affect a rabbit’s nervous system.
The study was simple.
The researchers gathered two groups of companion rabbits at a veterinary clinic – one as a control and the other to lay in the dorsal position in an attempt to induce tonic immobility.
Upon entering the clinic, each group of rabbits had their glucose and cortisol levels tested via blood from the marginal vein in the ear and had their respiratory rate, heart rate, and pupil size noted.
Then, they underwent a detailed clinical evaluation in their respective positions (upright for the control group, and dorsal for the study group) for approximately 5 minutes, before being blood tested and having their vitals assessed a second time.
After a waiting period of 15 minutes, their blood was taken again and data was collected for a third time.
The Results? – Not What You’d Think!
Over the course of the exams, the control group experienced an average increased respiratory rate (+17%), pupil size (+11%), blood glucose concentration (+10%), and blood serum cortisol concentration (+78% across the entire group) and a decrease in heart rate (-9%).
The study group, however, experienced an increase in zero testing factors (on average), while they decreased in heart rate (-12%), pupil size (-9%), and blood glucose concentration (-7%). Their blood serum cortisol concentration decreased in 6 rabbits (-20%) and increased in the remaining 4 (+53%).
What Does That Mean?
When both groups were compared, the rabbits evaluated in a normal position showed data indicating higher levels of stress, versus the study group that had been held on their back!
“The main stress marker, serum cortisol concentration, increased in all control group rabbits and only in 4 study group animals. This indicates that corticoliberin (CRH) and adrenocorticotropin (ACTH) are not produced during TI, which means that lying on the back is not a stress factor for most rabbits,” the study describes.
They also noted an increase in blood glucose concentration in the control group, which is consistent with rabbits experiencing presumed stress-induced hyperglycemia.
“Similarly, the glucose concentration in the control group increased between the first and third measurements, whereas a general decrease in serum concentration was observed in the study group rabbits. In rabbits, as in other animal species, hyperglycaemia can be caused by stress. In a study by Harcourt-Brown, 58% of rabbits showing signs of hyperglycaemia also had elevated levels of this sugar. Although there are no reports of the exact mechanism by which hyperglycaemia develops, many authors confirm its occurrence in animals exposed to pain or situations that may cause stress, such as transport and some research procedures.”
In other words, the rabbits examined in the normal standing position had harsher indicators across multiple data points, each with a high correlation to stress.
So, is laying rabbits on their back as harmful as many claim it to be?
The evidence says no! In fact, it even points to properly-maneuvered dorsal restraint as a beneficial handling method for minimizing stress!
“Our observations allowed us to conclude that those of the rabbits admitted to the veterinary clinic which underwent clinical examination in a standard position were more stressed than the animals under TI. Tonic immobility induced by inversion of the animal on its back is a safe method of rabbit restraint, greatly facilitating clinical examination and other diagnostic procedures for veterinarians and minimizing the risk of injury due to improper taming methods.”
Rest assured that, when taking proper care of your rabbits, cradling them on their back is both easier for you – and them!
*As a side note, it’s important to understand that the techniques of the original 1975 and 1977 studies by Michael Woodruff, Daniel Hatton, et al. are not the same techniques used to induce TI today. Whereas rabbits were previously slammed down into wooden troughs with hands around their neck to cause systemic fear response, today’s TI induction technique is simply gentle inversion into the dorsal position. Therefore, the previous studies are not reliable indicators of stress levels in non-abusive settings.
Citations
Wilczyńska, Anna & Ziętek, Jerzy & TEODOROWSKI, OLIWIER & WINIARCZYK, STANISŁAW & Adaszek, Lukasz. (2021). Effect of tonic immobility induction on selected physiological parameters in Oryctolagus cuniculus f. Domesticus rabbits. Medycyna Weterynaryjna. 77. 295-299. 10.21521/mw.6541.
Woodruff, Michael. (1977). Limbic Modulation of Contact Defensive Immobility (“Animal Hypnosis”). The Psychological Record. 1. 161-175. 10.1007/BF03394439.
Hatton, Daniel & Woodruff, Michael & Meyer, Merle. (1975). Cholinergic modulation of tonic immobility in the rabbit (Oryctolagus cuniculus). Journal of comparative and physiological psychology. 89. 1053-60. 10.1037/h0077191.
Hayyy Farms 
Very informative. Thanks Hayley.
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