TORTOISE: PREPARING FOR HIBERNATION
Introduction
The key to maintaining any exotic pet in captivity is to imitate his/her natural
environment as closely as possible. This does not mean providing a captive situation
which looks from our perspective like the wild one, but rather one to which
the animal's anatomy and physiology is adapted. Mediterranean tortoises are
in a difficult situation; they can normally survive in a cool summer and can
be fed on vegetable matter but without careful maintenance over the winter they
can die. This means preparing them for hibernation, assessing whether they are
fit to hibernate, giving them appropriate hibernation conditions, monitoring
them during hibernation and then being prepared to treat them for post-hibernational
problems.
Mediterranean tortoises hibernate in their normal southern Mediterranean climate,
but only for a limited time. In cool countries the cold is often too long for
hibernation to be uneventful. Also, the summer is not always warm enough to
allow a good nutritional and metabolic plane to be reached. For these reasons
every tortoise should be given a veterinary examination before hibernation is
started. If a tortoise shows any clinical abnormalities it is foolish not to
undertake as full an assessment as possible and this may mean taking a blood
sample or an X-ray.
The time to act
The autumn equinox is a watershed in deciding whether to commit a tortoise
to hibernation. By this time he should have been checked, weighed and prepared
for hibernation or taken into a warm environment for over wintering. He should
not have eaten within two to four weeks of hibernation, since undigested food
in the intestine ferments and causes considerable problems. He should, however,
be encouraged to drink since dehydration can be a significant problem during
hibernation.
Simple weighing and measuring
One of the critical, yet very easy, steps that should be performed when considering
whether to hibernate a tortoise is to weigh and measure the animal. In the 1970's
Dr Oliphant Jackson devised a simple graph showing what the optimum weight should
be at any given length of shell for Mediterranean tortoises. The weight of the
tortoise divided by the shell length, the Jackson ratio, is now well known and
your veterinary surgeon will have a graph. This graph will indicate whether
your tortoise has put on enough weight over the summer to be able to hibernate.
Clinical evaluation
Your veterinary surgeon will want to look in your tortoise's mouth and ensure
there is no infection, no discharge from the nose or any other orifice and feel
the hindlimb musculature and the abdomen where the limb exits through the shell.
This is to ensure that there is sufficient body mass which is a little difficult,
given that the shell hides so much of the body. A tortoises loses about 1% of
his bodyweight per month of hibernation so one below the optimum Jackson ratio
will lose too much, especially where hibernation occurs for up to six months.
Thus, an underweight tortoise should not be allowed to hibernate. An overweight
animal is unlikely to have excess muscle or fat gain but to have retained fluid,
perhaps because of liver or kidney abnormality. Clearly this and any ill tortoise
should be fully investigated and over wintered indoors, not hibernated.
Preparing the hibernating animal
A tortoise whose hibernation is deemed safe should be prevented from feeding
for, as we said above, from two to four weeks but allowed to drink as much as
he requires. In the falling temperatures of autumn a reduction in feeding is,
anyway, to be expected. The optimal temperature in which to keep a tortoise
is 5°C, while below 2°C are dangerous because of freeze-related disease. Above
10°C precipitates activity and anyway encourages over metabolism, with weightloss
of over 1% per month.
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