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 British 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. The cold in this country 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 (or if he or she does not it is in the British Small Animal Veterinary Association's Exotic Pets Manual which should be on the book shelf!) 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 5ºC, while below 2ºC are dangerous because of freeze-related disease. Above 10°C precipitates activity and anyway encourages over metabolism, with weightloss of over 1% per month.
Managing hibernation
This is covered in more detail in a leaflet concerning hibernation itself but here it should be said that more and more tortoise owners are artificially extending the autumn, both in terms of light and temperature so that the tortoise is not hibernated until perhaps mid-December.
Ark Veterinary Centre