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Madkins007

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I am writing an article on building strong bones and shells in tortoises, and would very much like some feedback from the community. The target audience would be beginning and intermediate keepers of most species of tortoises.

The original article uses some formatting commands that did not translate to this format, so forgive any 'artifacts' because of that.

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Building Strong Skeletons and Shells:
The importance of calcium, vitamin D, UVB, and other elements

By Mark Adkins

All vertebrate animals have bones made mainly of calcium, and keeping their skeleton and our tortoises's shell healthy is an important part of a keeper's job. If we fail in some part, our tortoises can suffer from soft shell, pyramiding, metabolic bone disease, deformities, improper growth and development, organ problems, and even death. Thankfully, if we provide the basics, they will do the rest!

Healthy bones are built about the same way for tortoises as for humans. The basic formula is:
- 2 parts of calcium
- 1 part of phosphorous
- Vitamin D
- Trace elements like iron, magnesium, and other nutrients
- Heat, and
- Water

Calcium is a critical element in strong bones. Most animals, including tortoises, get calcium from eating calcium-rich plants or from other animal's bones and tissues. Generally, the darker green and 'grittier' a plant is, the more calcium it contains. On the other hand, the fruits that forest tortoises like so much are generally very low in calcium, except for figs, papaya, and cactus fruit. Most nutritional databases and labels include the amounts of calcium in a food item to help us in our planning.

Calcium gives bones their basic structure, but it is also critical in building tissues, the workings of many organs and so on, so too little calcium will affect the tortoise in many, many ways besides just the skeleton. Too much calcium, on the other hand, is usually washed from the system harmlessly as long as the animal has adequate vitamin D and water. Too much calcium and too little vitamin D and water can create bladder stones and other problems.

Phosphorous is needed because calcium alone makes for brittle bones. Phosphorous gives bone a little flexibility and strengthens them. We want to offer a ratio of about 2 parts calcium for every part of phosphorous in the diet. This is called the 'Calcium:phosphorous Ratio', abbreviated as 'Ca: P'. A good Ca: P would be 2:1. We almost never need to add phosphorous since most grocery store foods have it in abundance.

Supplemental Calcium can help us ensure that our tortoises are getting a 2:1 ratio over time. Not every bite of food has to have a 2:1 ratio, but the trend over a week or so should aim for that goal. Since a lot of grocery store foods are low in calcium, we either need to use high calcium foods or supplemental calcium. The best is 'calcium carbonate' powder. While these calcium particles are rather large and not absorbed as well as some other forms, it still works for our needs, and is cheap and safe. You can get it at most pet stores or drug and health food stores. One cheap source of pure calcium carbonate is the NOW! brand calcium supplement sold at many health food stores. Cuttlebone sold for pets is another, more edible, form of calcium carbonate that some tortoises love and others ignore.

There are several other forms of supplemental calcium, but most of them have some negative elements. Egg shells, for example, are sharp, gritty, and can contain heavy metals and other undesirable elements. Bonemeal has phosphorous in it. Calcium from coral is just an expensive form of calcium carbonate. 'Calcium ciltrate' is a smaller particle and easier to absorb, but it is less 'rich' so it takes more to accomplish the same goals and costs more.

How often? Most keepers prefer to offer high calcium foods and just use the supplement lightly one to three times a week. I usually add a small pinch to any meal I believe to be below the 2:1 ratio. Remember- use it lightly and make sure there is enough vitamin D and water. If your tortoise is dehydrated, take care of that first.

Vitamin D is required by all vertebrates so the body can actually use the calcium. There are two main forms of vitamin D:
- Vitamin D2 is obtained from plants, fungi, and invertebrates (worms, insects, etc.). D2 is not as biologically useful as the other main form is- it takes more of it to do the same job, and it does not last or work for as long. Many forest-dwelling chelonians eat a lot of fungi and invertebrates, so they may get some of their vitamin D needs this way in the wild, but most of the worms and mushrooms we can buy are not as rich in D2 as wild sources are.
- Vitamin D3 is a more powerful, more useful form of D that is found in the oil of fatty fish, or in eggs, organ meats, and to a smaller extent, in other red meats. It is also added to many foods, like pellets and kibbles. The most useful form of D3 is made in the skin when it is exposed to a specific type of ultra-violet light called 'UVB' for even a few minutes a day.

Research on the effectiveness of D2 and dietary D3 is inconclusive so far- and few studies have been done on tortoises- but the studies suggest that even if they work, they do not work as well as the D3 made in the skin. We are also not sure about the needs of hatchling tortoises, which spend so much of their time hiding. They may get all they need from their diet or even the yolk sac, and too much UVB is probably bad for their eyes, but offering some low level UVB for at least a while each day while making sure they can hide away from it seems like a safe and smart option.

UVB Light is a part of sunlight and can be provided by some specialty light bulbs. Ultraviolet light is broken down into several parts.
- UVA are the waves closest to regular violet and are the most common. This is what plain 'UV bulbs' and black light bulbs produce. UVA helps promote basking and other natural behaviors but does not help with calcium.
- Next is UVB, which besides making D3 also helps kill germs, promote natural behaviors, can hurt eyes, and causes sunburn. This mix of good and bad effects is why we don't want to overdo things.
- There is also UVC which does not generally pass through the atmosphere but is artificially made as a sterilizing agent.

Too much of any UV light can cause skin, eye, and DNA damage as well as fading fabric, aging plastic, and so on. We always want to make sure that we are using the right type and strength of light for our purposes, and that we always provide shade and hiding places. We also need to remember the rest of the 'healthy bone formula' since UVB will not solve everything on its own.

We don't generally worry about too much or little UVB outdoors since natural UVB is self-regulating to make sure the animal does not get too much vitamin D3, but the animals still need to be able to get to shade when they want it to avoid other concerns.

Less than 10% of the UVB rays can pass through most glass or plastics, so sunlight through a window is really not enough. (Annoyingly enough, UVA does pass through glass.) For tortoises kept indoors, there are a wide variety of UVB lamps. It is best to do research so you can get the best lamp for your situation- how much UVB do your tortoises need (or would get in the wild), how big is your habitat, do you need supplemental heat or not, etc. Sites like http://www.uvguide.uk.com can help. Be sure to follow the manufacturer's instructions for mounting and replacing the bulb to help minimize the negative effects of UVB. A couple other options would be to take their tortoises outside for short periods on sunny days in the winter (like holding them in their warm hands, or in a cooler with a heat source), or to use UV-transparent plastics like Plexiglas UV-T or Acrylite OP-1 or OP-4 in your windows and enclosures.

Vitamin D Supplements should generally be avoided if possible since they a.) possibly do not help, and b.) are 'fat soluble' vitamins (along with A and E) where excess gets stored in the fatty tissues and can actually poison the animal. Vitamin D overdose looks a lot like a sunburn- redness, soft tissue peeling, etc. While we do not know the specific amounts of D our tortoises need, it is not very much. On the other hand, if your tortoise has no access to UVB light, you may need to consider this option. First try to offer foods with both D2 and D3, and only offer supplemental D3 if needed. Then the problem is to make sure each tortoise gets a little and none gets too much. UVB light is usually better.

Trace Elements like iron, magnesium, and so forth help round out the calcium cycle. Animals should get these through their diets. A little multi-vitamin/mineral supplement once a week or less can help ensure that they are getting what they need if you cannot offer a varied, balanced diet.


Heat is critical for tortoises to digest foods and use all nutrients correctly. Heat basically activates the entire process- no heat, no calcium utilization cycle. While different species have different needs, it is always best to offer a variety of temps and settings so they can choose what they want. Make sure the floor of the indoor habitat is not too cool, especially where they sleep.

Water helps the calcium reach throughout the body, and makes it easier to flush out any excess so it does not build up in the tissues. Water also helps prevent pyramiding, in which the skeletal structure of the raised areas of the shell look more like sponge than bone.

Many pet tortoises are at least a little dehydrated for many reasons, including just the stress of captivity. A dehydrated tortoise will feel light for its size, and as things get worse, the eyes will get teary, the skin will appear dry and flaky, the eyes will start to 'sink', and it will eventually die. One way to tell if your tortoise is dehydrated early is to use the 'Donahue Formula'. Your tortoises length in centimeters to the third power, times 0.191 gives the minimum weight in grams we should see. (Written another way, it is "length in cm^3 x 0.191 = weight in gr".

Providing water for tortoises is sometimes tricky- wild tortoises often maintain their hydration in ways that can be difficult to duplicate in captivity. Depending on the species, we can try:
- Drinking water. In general, a tortoise wants to reach down and submerge most of its head to drink so keep that in mind as you plan your drinking dish- but also remember that many species are clumsy in water. Offer plenty of fresh water daily, even if all it does is to use the dish as a toilet. Try to offer a water dish big and deep enough that the tortoise can soak in it if it wants- soaks also help with hydration.
- Humid hide. A small, semi-enclosed, dark, warm space can be kept very humid and simulate a natural burrow. There are many ways to do this but a simple option is to cut a hole in the side of a plastic box or tub with a lid and put some fluffy material in there. Park the box in a warm part of the habitat. Sew a big handful of sphagnum moss in a cloth bag, soak it in warm water, and hang it in the box- resoak it as needed.
- Overall humidity. Indoor habitats are often too dry (dry wintertime indoor air, forced air heating, heat lamps, etc.). Most species, including humans, feel better at about 50% relative humidity. Forest species like high humidity- in the 90% range or more (although that can cause its own problems, like mold).
- Microhabitats. Even tortoises that do not tolerate much humidity can appreciate a nap in the humid shade of a plant. Offering live plants, humid or damp areas, and so forth lets the tortoise choose what it needs. Misters, vaporizers, or drippers can be used to make humid spots. (Note: most misting or vaporizing systems cool the air- make sure you are not chilling your animals.)
- Rain. Mimicking a warm rain stimulates many species to come out, drink, and soak in puddles. This is not always possible, but can be fun when it is.
- Moist food. Most grocery store produce is a lot drier than you think, and looses even more in the fridge. Soaking greens in cold water helps a lot, and many foods can be served lightly misted. Don't forget that the stalks hold a lot of water. Fruit-loving forest tortoises can get quite a bit of moisture from some of the wetter fruits, and most tortoises enjoy water-rich cactus pads.
- Frequent soaks. If none of the other techniques are helping, you can also soak your tortoise in warm, shallow water for up to about 30 minutes at a time as needed. 'Forced' soaks can be stressful, so don't overdo them.

This sounds like a lot of work, but in reality, once you get things going well, everything pretty much takes care of itself. Offer a diet that gives the tortoise the nutrients it needs, offer it some natural or UVB lighting, keep it properly warm and well-hydrated, and everything should work out fine for your tortoise for years to come.

Sources:
- Wikipedia articles on: calcium, ultraviolet light, vitamin D, and humidity.
- "The Redfoot Manual" by Mike Pingleton (www.pingleton.com). Donahue formula and general information.
- Many discussions at www.tortoiseforum.org and on the Yahoo! Redfoots Group.
- www.UVGuide.uk.com
- "Reptile Medicine and Surgery" edited by Dr. Douglas Mader

Note: My main goal here is to help new and intermediate keepers better understand the issues involved with healthy bones. My main background and interests are in the Red-foot and forest tortoises, but I tried to make the article useful for all tortoise keepers.

Mark Adkins (c) 2009

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There ya go. Any feedback is welcome.
 
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Maggie Cummings

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I agree with the rest, your article is well thought out and will be very helpful...
 

Madkins007

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Maggie- I was thinking of you on the whole bladder stone/hydration issue. Did I hit it properly in your opinion?
 

bettinge

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Great article Mark!

I found something "Very debatable" written by what I believe to be a well regarded author on Tortoises. I don't really agree with it, and I think most on this forum wont agree with it either.

On page 138 of "Hermanns Tortoise" by Holger Vetter, he suggests NOT supplementing food with calcium of any kind, but rather always make calcium available via cuttlebone, etc. Let the tortoise regulate their intake! He goes on to say about supplementing "this forces the calcium on them, and nobody is really certain about what might be a proper dosage. It could therefore be that in the end you cause more damage than good"!

What are your thoughts? Could one day adding calcium to food be viewed the same as we now view people not offering water to torts in years past. It was well documented (years ago)that tortoises did not need water. Its well documented today that food should be suplemented with calcium powder! Is it reasonable to question forced calcium supplements, or should we accept it as fact?

You do say that too much calcium is safe with adequate vitamin D and water. Also, why would we think a tortoise would know what they need, humans can't even do that. Many, if not most humans are calcium deficient, maybe from our poor diets!
 

Redfoot NERD

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bettinge said:
Great article Mark!

I found something "Very debatable" written by what I believe to be a well regarded author on Tortoises. I don't really agree with it, and I think most on this forum wont agree with it either.

On page 138 of "Hermanns Tortoise" by Holger Vetter, he suggests NOT supplementing food with calcium of any kind, but rather always make calcium available via cuttlebone, etc. Let the tortoise regulate their intake! He goes on to say about supplementing "this forces the calcium on them, and nobody is really certain about what might be a proper dosage. It could therefore be that in the end you cause more damage than good"!

What are your thoughts? Could one day adding calcium to food be viewed the same as we now view people not offering water to torts in years past. It was well documented (years ago)that tortoises did not need water. Its well documented today that food should be suplemented with calcium powder! Is it reasonable to question forced calcium supplements, or should we accept it as fact?

You do say that too much calcium is safe with adequate vitamin D and water. Also, why would we think a tortoise would know what they need, humans can't even do that. Many, if not most humans are calcium deficient, maybe from our poor diets!

Could it be.. tortoises are much smarter than humans???
 

Stephanie Logan

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Thanks for a very insightful and well-oreganized article. I wonder if "calcium ciltrate" is supposed to be "calcium citrate", or maybe I have just been mispronouncing it all this time!

You article is especially appreciated by me, because I am the one with a severely pyramided tortoise, who got that way from poor diet, little exercise, inadequate water, no humidity at all, and very little calcium! I am doing my best to ensure any remaining gowth in Taco's shell is healthy growth!
 

bettinge

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Also, why would we think a tortoise would know what they need, humans can't even do that. Many, if not most humans are calcium deficient, maybe from our poor diets!

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Could it be.. tortoises are much smarter than humans???
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I think you may be right!
 

Madkins007

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bettinge said:
Great article Mark!

I found something "Very debatable" written by what I believe to be a well regarded author on Tortoises. I don't really agree with it, and I think most on this forum wont agree with it either.

On page 138 of "Hermanns Tortoise" by Holger Vetter, he suggests NOT supplementing food with calcium of any kind, but rather always make calcium available via cuttlebone, etc. Let the tortoise regulate their intake! He goes on to say about supplementing "this forces the calcium on them, and nobody is really certain about what might be a proper dosage. It could therefore be that in the end you cause more damage than good"!

What are your thoughts? Could one day adding calcium to food be viewed the same as we now view people not offering water to torts in years past. It was well documented (years ago)that tortoises did not need water. Its well documented today that food should be suplemented with calcium powder! Is it reasonable to question forced calcium supplements, or should we accept it as fact?

You do say that too much calcium is safe with adequate vitamin D and water. Also, why would we think a tortoise would know what they need, humans can't even do that. Many, if not most humans are calcium deficient, maybe from our poor diets!

I'm not anywhere close to being able to answer this with authority, but Dr. Mader and other authors seem to believe that excess calcium is excreted out, as it is in humans, as long as the animal is properly hydrated. I DO know that one big problem most keepers have is that the foods we have access too do not have the same nutritional levels, or as much calcium, as wild foods have.

If we COULD offer a diet that was routinely about 2:1 Ca: P, then this would be a non-issue. Since we can't, I am not sure what harm there is in LIGHT supplementation of an animal in good health otherwise.


As for the "Also, why would we think a tortoise would know what they need, humans can't even do that." comment- that is not quite right. Humans, tortoises, and many other animals often have cravings that are driven by dietary needs. Some animals seek out banks of certain types of soil for trace elements, humans crave certain foods that their bodies feel they need, etc.

Certainly, I think humans have screwed up our ability to sense what we need with all of the non-foods, processed foods, and quasi-foods we eat, but I think the basic drive is still there to some degree.

Stephanie Logan said:
Thanks for a very insightful and well-oreganized article. I wonder if "calcium ciltrate" is supposed to be "calcium citrate", or maybe I have just been mispronouncing it all this time!

You article is especially appreciated by me, because I am the one with a severely pyramided tortoise, who got that way from poor diet, little exercise, inadequate water, no humidity at all, and very little calcium! I am doing my best to ensure any remaining gowth in Taco's shell is healthy growth!

Thanks for catching the typo.

I bet Taco will turn out fine!
 
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