UPDATED/EDITED 1-5-2012
Susan Donoghue, DVM wrote an article about tortoise weights in 1997- "Nutritional status of tortoises using morphometrics to assess body condition".Vivarium magazine, Volume 8 Number 2, in which she offers is the helpful formula "SCLcm^3 x 0.191 = tWTgr", where SCLcm is 'Straight-line carapace length in centimeters' and tWTgr is 'Target weight in grams'. (See the end of the article for advice on getting a good SCL).
The data is based on 76 tortoises and box turtles representing 11 species, and works fairly well even for young tortoises.
We are going to make this formula more 'user friendly' by using it to calculate the tortoise's Body Mass Index, the BMI that all dieters are familiar with. Because this is tailored for torts, we are going to call it the tBMI.
tBMI= cWTcm/tWTgr (or SCLcm^3 x 0.191)[/b]
EXAMPLE:
A tortoise with a straight-line carapace length (SCL) of 12.3 centimeters and a cWTgr (current weight in grams) of 349.
- The tWTgr is 355.425597 (12.3^3x0.191)
- 349/355.4= 0.982
- tBMI= 0.982
(Note- Google do all the work for you if you type in "[current weight in grams]/([SCL in centimeters]^3x0.191)=". The answer you get will be the tBMI.)
RESULTS:
You can determine if your tortoise is normal, dehydrated, or obese based on these results. Note- the figures used below are extrapolated from several sources and should be used as guidelines only!
- 0.66 or lower: There is less than a 2.5% chance that this tortoise is healthy at this weight. It is probably very dehydrated and/or underfed and should be seen by a vet.
- 0.66 to 0.83: There is only about a 15% chance that this tortoise is healthy at this weight. It is probably dehydrated and/or underfed and needs appropriate care.
- 0.83 to 1.00: This is a normal range, but statistically a little underweight, which may signal mild dehydration and/or being underfed. Review and correct cares and diet as appropriate.
- 1.00 to 1.16: This is a normal range, but statistically a little overweight, which may signal mild overfeeding. Review and correct cares and diet as appropriate.
-1.16 to 1.33: There is only about a 15% chance that this tortoise is healthy at this weight. It is probably at least somewhat obese and needs appropriate care.
1.33 or over: There is less than a 2.5% chance that this tortoise is healthy at this weight. It is probably obese and needs appropriate care.
RESOURCES:
- http://www.tortoiselibrary.com/ for articles on hydration/dehydration, a bibliography, and more
- BARTHEL, Tom “The Hydration Equation†Reptiles, July 2007
- DONOGHUE, Susan,1997. "Nutritional status of tortoises using morphometrics to assess body condition".Vivarium magazine, Volume 8 Number 2
- MADER, Douglas R., DVM, ed. "Reptile Medicine and Surgery". Saunders Elsevier, 2nd Edition 2006.
APPENDIX: Getting a good SCL reading.
The easiest way to get a good SCL without tools like calipers is to...
1. Place a metric ruler on the floor, '0' against the wall.
2. Set the tortoise on the ruler, head towards the wall, and position it so the shell touches the wall.
3. Place a block, box, etc. behind the tortoise, on the ruler, and move it so it touches the back of the tortoise's shell.
4. Move the tortoise and read the ruler at the block.
(Note- if the ruler has a space beside the '0' mark, you should either cut the ruler down so '0' is on the end, or remember to subtract the size of the gap from the final measurement... or cut the end off so '0' in on the end!)
Susan Donoghue, DVM wrote an article about tortoise weights in 1997- "Nutritional status of tortoises using morphometrics to assess body condition".Vivarium magazine, Volume 8 Number 2, in which she offers is the helpful formula "SCLcm^3 x 0.191 = tWTgr", where SCLcm is 'Straight-line carapace length in centimeters' and tWTgr is 'Target weight in grams'. (See the end of the article for advice on getting a good SCL).
The data is based on 76 tortoises and box turtles representing 11 species, and works fairly well even for young tortoises.
We are going to make this formula more 'user friendly' by using it to calculate the tortoise's Body Mass Index, the BMI that all dieters are familiar with. Because this is tailored for torts, we are going to call it the tBMI.
tBMI= cWTcm/tWTgr (or SCLcm^3 x 0.191)[/b]
EXAMPLE:
A tortoise with a straight-line carapace length (SCL) of 12.3 centimeters and a cWTgr (current weight in grams) of 349.
- The tWTgr is 355.425597 (12.3^3x0.191)
- 349/355.4= 0.982
- tBMI= 0.982
(Note- Google do all the work for you if you type in "[current weight in grams]/([SCL in centimeters]^3x0.191)=". The answer you get will be the tBMI.)
RESULTS:
You can determine if your tortoise is normal, dehydrated, or obese based on these results. Note- the figures used below are extrapolated from several sources and should be used as guidelines only!
- 0.66 or lower: There is less than a 2.5% chance that this tortoise is healthy at this weight. It is probably very dehydrated and/or underfed and should be seen by a vet.
- 0.66 to 0.83: There is only about a 15% chance that this tortoise is healthy at this weight. It is probably dehydrated and/or underfed and needs appropriate care.
- 0.83 to 1.00: This is a normal range, but statistically a little underweight, which may signal mild dehydration and/or being underfed. Review and correct cares and diet as appropriate.
- 1.00 to 1.16: This is a normal range, but statistically a little overweight, which may signal mild overfeeding. Review and correct cares and diet as appropriate.
-1.16 to 1.33: There is only about a 15% chance that this tortoise is healthy at this weight. It is probably at least somewhat obese and needs appropriate care.
1.33 or over: There is less than a 2.5% chance that this tortoise is healthy at this weight. It is probably obese and needs appropriate care.
RESOURCES:
- http://www.tortoiselibrary.com/ for articles on hydration/dehydration, a bibliography, and more
- BARTHEL, Tom “The Hydration Equation†Reptiles, July 2007
- DONOGHUE, Susan,1997. "Nutritional status of tortoises using morphometrics to assess body condition".Vivarium magazine, Volume 8 Number 2
- MADER, Douglas R., DVM, ed. "Reptile Medicine and Surgery". Saunders Elsevier, 2nd Edition 2006.
APPENDIX: Getting a good SCL reading.
The easiest way to get a good SCL without tools like calipers is to...
1. Place a metric ruler on the floor, '0' against the wall.
2. Set the tortoise on the ruler, head towards the wall, and position it so the shell touches the wall.
3. Place a block, box, etc. behind the tortoise, on the ruler, and move it so it touches the back of the tortoise's shell.
4. Move the tortoise and read the ruler at the block.
(Note- if the ruler has a space beside the '0' mark, you should either cut the ruler down so '0' is on the end, or remember to subtract the size of the gap from the final measurement... or cut the end off so '0' in on the end!)