Tortoise Weight Formula- tBMI

Status
Not open for further replies.

Baoh

Well-Known Member
10 Year Member!
Joined
Nov 18, 2007
Messages
1,827
Location (City and/or State)
Florida
Madkins007 said:
OK, so enough of this banter. Bottom line- is the idea of a tool like this beneficial to some degree, when properly explained, and is it explained properly? What can we do to make something useful from all this?

Okey dokey.

Yes (to some degree), yes (when explained in proper context), and I would just call these average good ranges for overall weight for some species. I would not say it says anything about hydration or anything else other than overall weight of some animals as a "rule of thumb" based on limited, but well intended, data.

I would not use it, personally, and would not want a person to live and die by it, but it can provide a sense of "goodness" for the heft of an average animal when they do not have a large enough history to have formed much perspective. For such people, I think it may help guide them.
 

Madkins007

Well-Known Member
Moderator
10 Year Member!
Joined
Feb 15, 2008
Messages
5,393
Location (City and/or State)
Nebraska
Dang. Sorry, but I am going to go back on my 'enough of this banter' gag. I am really enjoying this discussion and your insights, even being well outside my skill area.

I'm reluctant to dismiss the idea that it can help, even if to a limited extent, signal dehydration. That was one of the driving purposes behind her research- trying to determine a relationship between mass and dehydration so people have something more useful than 'feels heavy' to go buy.

I was thinking about your points and realized one thing that may be an interesting detail- human growth/mass/composition is not physically constrained by much- we are basically a loose leather bag filled with lots of wet gunk. A tortoise is constrained by the slow-growing shell. Also, mammal metabolism is 2-4 times faster than reptilian, so changes happen much faster. I wonder if these two points limit how variable the tissue composition can be.

Many of your examples involve people who lay on the outskirts of the 'normal range' -but remain healthy- because of special circumstances, such as the athlete who spends lots of time pushing the envelope of how much they can lift or how fast they can run, etc. Tortoises do not work out beyond exploring their range. Perhaps we do not have as many examples of 'healthy but abnormal' in this situation as we would in humans.
 

Zamric

Well-Known Member
5 Year Member
Joined
Oct 29, 2011
Messages
3,290
Location (City and/or State)
The Crystal Unicorn
I think being able to determin proper weight-vs- shell size is a very important in determining hydration. the shell doesn't expand and contract to give a visual sign of physical delima. Some signs like foaming eyes can hint to dehydration problems but weight could be the best determining factor. If a gallon of water weighs 8.5 lbs, then a dehydrated adult tort could gain over 5 lbs with a couple of soaks and drinks. These guys are like prehistoric sponges but hold water better. we just have to have an accurate starting point!
 

GeoTerraTestudo

Active Member
5 Year Member
Joined
May 7, 2011
Messages
3,311
Location (City and/or State)
Broomfield, Colorado
Great thread, Mark. And yes, I do take monthly weight and SCL measurements for my pair of steppe tortoises, and compute their tBMI. The Donoghue equation computes the minimum healthy weight for brumation (which is affected by hydration, fat, and bone density), but not the maximum. Because steppe tortoises have short, round, flattened shells, the Donoghue equation appears to be overestimating their condition. To get them to a visibly healthy weight, it seems like they have to be at a tBMI of at least 150%. I don't suppose you know of a correction factor for this and other "unusualy shaped" tortoise species, do you?
 

Madkins007

Well-Known Member
Moderator
10 Year Member!
Joined
Feb 15, 2008
Messages
5,393
Location (City and/or State)
Nebraska
That I don't Geo. However, I wonder if you are thinking of the Jackson Ratio (WTgr/SCLcm^3, where a result of about 0.21 is optimal for Mediterranean torts to brumate)? Donoghue's formula was developed to help vets determine which individual tortoises undergoing treatment needed hydration support.

Based on the original article, Dr. Donoghue used the formula successfully on 76 individuals over 11 species, ranging from pancakes to Eastern box, so I suspect that it holds for most.

Can you toss me some weights and SCLs so I can play with the numbers myself?
 

qcpunk

New Member
5 Year Member
Joined
Oct 2, 2011
Messages
33
Location (City and/or State)
Queen Creek, AZ
What an interesting thread everyone!! I just read over everything and think this is a great discussion!

I believe the next step would be to draw from our fellow members to see if we can either validate, dismiss, or correct the theories.

My Sulcata hatched around mid August 2011, so is nearly a year old. Its length is 12cm(4.7") with a weight of 385 grams.

Based on the calculations, the tWT is 330.048 grams, and this calculates to aprox 1.16 BMI.

My hope is that if other members post thier data, we may be able to draw some conculsions based on data trending.

Cheers everyone!! :D
 

GeoTerraTestudo

Active Member
5 Year Member
Joined
May 7, 2011
Messages
3,311
Location (City and/or State)
Broomfield, Colorado
Madkins007 said:
That I don't Geo. However, I wonder if you are thinking of the Jackson Ratio (WTgr/SCLcm^3, where a result of about 0.21 is optimal for Mediterranean torts to brumate)? Donoghue's formula was developed to help vets determine which individual tortoises undergoing treatment needed hydration support.

Based on the original article, Dr. Donoghue used the formula successfully on 76 individuals over 11 species, ranging from pancakes to Eastern box, so I suspect that it holds for most.

Can you toss me some weights and SCLs so I can play with the numbers myself?

Ah, the Jackson Ratio. I was not aware of that. Thanks! I will use it in autumn or winter when evaluating whether to let Mork and Mindy brumate or not.

Re: tBMI in Russian tortoises
Sure, Mark, and thank you! Here are the data I've been collecting on Mork and Mindy since I got them last spring.

Mork (male):
Date CL (cm) Mass (g) Min weight (g) Percent
05/22/2011 10.4 360 215 168%
06/19/2011 10.4 325 215 151%
11/01/2011 10.6 330 227 145%
03/25/2012 10.6 347 227 153%
04/21/2012 10.6 375 227 165%
05/12/2012 10.7 376 234 161%
05/19/2012 11.1 393 259 152%
06/16/2012 11.1 367 260 141%
07/07/2012 11.1 352 260 135%

Mindy (female):
Date CL (cm) Mass (g) Min weight (g) Percent
05/22/2011 9.5 325 164 198%
06/19/2011 10.4 310 215 144%
11/01/2011 10.4 335 215 156%
03/25/2012 10.4 427 215 199%
04/21/2012 11.0 484 254 190%
05/12/2012 11.2 540 268 201%
05/19/2012 12.1 548 339 162%
06/16/2012 12.4 523 365 143%
07/07/2012 12.4 516 365 141%
 

GeoTerraTestudo

Active Member
5 Year Member
Joined
May 7, 2011
Messages
3,311
Location (City and/or State)
Broomfield, Colorado
I just computed the Jackson Ratio for my steppe tortoise pair, and they are both well over 0.21. You said this was the optimal number for Mediterranean tortoises to brumate safely. Does that mean being a little over it is better, or is it better to be well over it?
 

mctlong

Well-Known Member
Moderator
5 Year Member
Joined
Oct 17, 2009
Messages
2,658
Location (City and/or State)
SF Valley, SoCal
I feel so old! I took math before everyone was using computers to write out formulas, so it took me awhile to figure out what "^" means. I'm pretty sure I got it now, exponent, right?

Okay, so the formula seemed to fit my RT okay, he got a tBMI of 1.16. That seems reasonable. It doesn't appear to work for sully hatchlings, either that or my hatchling (4.6cm, 36g) is morbidly obese with a tBMI of 1.9 :D
 

Madkins007

Well-Known Member
Moderator
10 Year Member!
Joined
Feb 15, 2008
Messages
5,393
Location (City and/or State)
Nebraska
tBMI does not work for hatchlings, which I thought we had made clear, but I could be mistaken

Geo- Thanks, I'll crunch the numbers... sometime. (in the middle of some other stuff right now.)

Jackson ratio- I really don't know- I don't know much about it, but here is a link to an article that may help- http://www.tortoisetrust.org/articles/jackson.html

qcpunk- the Donoghue formula is based on the work of a renowned expert in reptile nutrition, and the tBMI is just a different way to present her formula (not necessarily easier but perhaps more graphically). I am not sure there needs to be a lot more verification unless it can be done under at least somewhat controlled conditions.
 
Status
Not open for further replies.
TortoiseSupply.com

New Posts

Top