What is the Jackson Ratio?
The Jackson Ratio is a method of calculating whether or not a tortoise is at a healthy weight for its size. There is an optimum weight size ratio for tortoises. It can also be used to assess the tortoise suitability for hibernation.
The Jackson Ratio was created by Dr Oliphant Jackson, MRCVS, in 1976. He created the ratio and formula by recording the weights and measurements of a large number of sick and healthy Mediterranean tortoise. Both Testudo graeca commonly named Spur Thighed Tortoise and the Testudo hermanni or Hermann’s Tortoise where assessed as part of the data collection. From this Dr Jackson used this data to create the Jackson Ratio, which is now commonly used to assess a tortoises health.
It is very important to remember that the Jackson Ratio can only be used for the assessment of Testudo graeca and Testudo hermanni, which are tortoises they consider to be of average body morphology. Any tortoise that is not of average body morphology is not suitable to be judged by the Jackson Ratio and alternative methods should be sought.