Trancing a rabbit (See How do I trance my rabbit?) is used as a method for controlling the pet while doing some grooming to scent glands and toenails. I have received some questions about possible, long term cumulative negative effects, and I am looking for answers that document long term negative impacts to the rabbit.
Trancing is, for those unaware, the use of the natural fear state of prey animals to go into a near death-like state in order to convince predators that they are dead and should stop being attacked. This is called tonic immobility or TI for short. The immediate side-effects of coming out of TI include things like increased respiration, heart rate, and plasma corticosterone (a steroid found in many animals).
So, if you consider that that basic situation is that the rabbit has been put into a state of extreme fear and that the response after release is to escape and hide which, after all, is the purpose of TI in the first place, then the significant impact would be to its trust in humans and its willingness to engage in their surroundings. The impact would only get worse the more frequently the rabbit is tranced and when tranced for long periods of time.
In effect, the long term negative is to make the rabbit generally regular feel fear and anxiety in an environment that they can't get out of. The health impacts of that can include:
- Sudden death as a result of increased arterial hypertension, hypotension, and heart failure from increased adrenaline in the system. Basically, the rabbit might not actually trance at some point, they might actually die. Essentially scared to death.
- Exertional myopathy which is basically a muscle disease that can become acute through repeated stress and fear. There's a lot of potential problems that can result as a consequence of that as the linked abstract discusses.
- Immediate injury as a result of escaping from the situation post trance. The rabbit is in fear, its reactions will not be normal.
In general, I would resort to trancing in only absolute necessity and avoid using it in a regular fashion if it all possible.
So since I first read this question and the answer by John I have been trying to find some good research on this. A veterinarian friend of mine did have quite a bit of research on rabbit stress hormones and mortality, but there is not a great deal of research on this. It is assumed by some (as noted in the answer by John) that trancing is the same process that causes TI. And others disagree. You can count me in the disagree camp but I had no hard evidence just observation.
So I approached some of my friends, a veterinarian, a graduate student in endocrinology, and several breeders about the possibility of doing a study to answer this question. So we(Ok the Vet and the Student mostly) put together a plan on how to do a preliminary analysis to see if we could come up with a procedure that would be reproducible and testable.
What we came up with was testing several different rabbits and measuring levels of Cortisol. The details are a bit monotonous so I will summarize it here. We checked each rabbit about 30 minutes before trancing for control, then compared the levels with those immediately after trancing.
Our first test involved 24 rabbits in 4 different breeds The results showed that 12%(3) of the rabbits showed a significant increase in cortisol levels after trancing while 30%(8) showed slightly lower levels. With the remaining rabbits showing levels that were not substantially different from their control levels.
The second test involved 24 different rabbits but the same 4 breeds The results showed that 16%(4) of the rabbits showed a significant increase in cortisol levels after trancing while 38%(9) showed lower levels. With the remaining rabbits showing levels that were not substantially different from their control levels.
In the end over 200 different rabbits in 12 breeds were tested The the aggregate results showed that 13% of the rabbits showed a significant increase in cortisol levels after trancing while 34% showed lower levels.
However none of the rabbits approached the level of increase seen in necropsies that had been performed of rabbits that had suffered traumatic deaths, or that were believed to have been scared to death. The working theory right now is that the increases seen are comparable with just the stress shown by the rabbits from being picked up. And that the trancing did not add stress to the rabbits and may have even lowered it.
These results by themselves do not prove anything though. However it was enough information that is currently being used in an application for a grant to perform a full study which would explore more controls. She is hoping that the grant will be approved in time to start the study in the summer of 2015.
The indications of what we see here is that there can be no cumulative negative effects if there are no negative effects from the the act in the first place. It also indicates that while being similar to TI it may be a different process that is invoking a similar physical response.