About Pyramiding

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What is 'pyramiding'?

Pyramiding, or Pyramidal Growth Syndrome (PGS) is when the scutes on a tortoise's carapace form into little hills. Some species of tortoise, like the Indian star tortoise (Astrochelys elegans) or the geometric tortoises (Psammobates species) do this naturally and automatically, but most species of tortoise only show this in captivity.

If you look at a pyramided shell in cross-section, you see that the bone itself is making the bump and the fingernail-thin scute is just following it. The bone looks spongy and is full of holes instead of the normal tight layers it should be. Something is causing the bone to grow the wrong way. Because the bone is not growing in a healthy way, pyramiding is generally considered an MBD, a metabolic bone disease (MBD is a category of diseases and conditions, not a disease itself.)

It is not as serious of an MBD as things like 'Nutritional Secondary Hyperparthyroidism' (NSHP, aka 'soft shell', 'rubber jaw disease', etc.), and tortoises with PGS seem to live a perfectly normal life in all respects.

For a long time, people blamed too much protein in the tortoise's diet for the deformity, then some studies were done that showed that protein had little effect, but that high humidity could at least prevent it. This led to many people aggressively spraying the tortoises and habitats or finding other ways to massively boost the humidity. One theory about humidity was that tortoises spent a lot of time in humid burrows, so this was a reasonable action. Field studies done with Testudo species showed that this was really not the case, at least in tortoises from drier ecosystems. Unless there had been a heavy rain, the burrows were not much more humid than the dry air on the surface. Humidity may prevent PGS in captivity, but it was not what prevented it in the wild.

The key to understanding PGS seems to be in recognizing how tortoises live and grow in the wild. Most wild tortoises experience two main seasons when they are active- wet and dry. In the dry season, growth slows down and the tortoise spends much of the day foraging for small amounts of food that are generally high in calcium and fiber, but low in moisture, carbohydrates, and other nutrients. This diet, combined with the vitamin D3 from the sunlight, fuels slow, dense bone growth, shown by very tight and thin growth rings.

In the wet season, there is more food and more variety available- flowers, fruits, leaves, fungi, and more. More carbohydrates, more moisture, more of everything, often combined with less actual work to find it. This abundance, combined with 'building block' nutrients built-up over the dry season, fuels faster growth indicated by wider rings, about the same way that trees do it.

These two seasons work together to ensure that the bone will grow in nice, tight, interlocking and rock-solid layers, and the scutes will grow smoothly over it all.

In captivity, however, we do not offer clear seasons and associated diets. Most of our tortoises get about the same diet all year long, and it tends to be rather 'rich' in that it is usually high in moisture, carbs, calcium, etc.- especially when we supplement it. Our environments are harder to generalize, but we rarely match the seasons they would experience in the wild. In Nebraska, for example, our summer is sort of similar to the dry season for the South American red-footed tortoise (Chelonoidis carbonaria), then we move them into a house in the winter that is almost always low in humidity, so they get the dry season all winter, too.

Other things that can affect this are lights that are too bright or warm, lack of UVB lighting, enclosures and care programs that do not allow enough exercise, sleeping options that do not allow good rest, etc. Overall, we generally just do not offer conditions that encourage smooth, unified growth between bones, muscles, nerves, and scutes, so we get problems.

Preventing pyramiding

Many people think of tortoises as being easy pets to care for, like hamsters. In reality, for most people, keeping a tortoise means you need to learn to provide and manage the right temperatures, humidity, lighting, diet, available space, hides, and more. All of this takes time, research, practice, and money. One of the real values of a forum like this one is that others can share their ideas to accomplish these things!

1. Establish the right habitat. Make sure to offer enough space, then invest in making sure it is properly heated, humidified, and lit for its specie's needs. Use a substrate that supports their environmental needs and hides and shelters that allow restful, secure sleep. Make sure the air is always fresh, and that mold and mildew is discouraged.

Most of us messed this up when we were just starting, especially if we were using outdated information. It is also harder to keep some species in some parts of the world than it is in others- it takes a lot more work to offer a good warm/humid red-footed tortoise habitat in Canada than it does in Florida.

Humidity really is a key issue in many ways. Ambient humidity in most tortoise environments is about 40-50%, while it is often as low as 5% in a typical home in the northern US or Canada. The trick is to figure out where our local climates are inappropriate and find the best ways to correct it.

2. Offer the right diet. It is easy to feed a tortoise as if it was a mammal and overfeed it, especially with rich foods. There are lots of discussions about diet, amounts, supplements, etc. and it can get very confusing. A very basic solution is to think of the diet as two parts-
-- Part A is stuff like grasses, hays, edible plant leaves, flowers, cabbage, greens, stalks, and other things that are low in moisture and calories but high in fiber (and, whenever possible, calcium). Offer these foods fairly freely and most days.
-- Part B is the stuff that is higher in calories, moisture, etc. and will vary by species. This would include any forms of meat, fruits, most veggies, lettuces, and processed tortoise chows. These should be limited to either a very small serving a day, or offered as small servings every few days or even weekly.

Your tortoise will eat as much food as you offer since in the wild it has never needed to learn any sort of moderation, so it is up to us to limit their intake, while also making sure that their guts are full and they have something to look forward to every day.

3. Watch your tortoise. If the scutes start to show thickening or raising, re-evaluate your cares or ask for help. The earlier we catch it, the earlier we can try to correct it. Once pyramiding has happened, you cannot undo it, but you can keep it from getting worse and over time it will become less noticeable.

Helpful links and articles

- ADKINS, Mark. "Building Strong Bones and Shells", and "Metabolic Bone Disease", among others. The Tortoise Library.com [This is my website]
- FIFE, Richard. “Pyramiding in Tortoises” Reptiles Magazine website.
- HIGHFIELD, Andy C. "The Causes of Pyramiding Deformity in Tortoises." Tortoise Trust, 2010.
- PINGLETON, Mike. "Understanding Pyramidal Growth Syndrome (PGS) in Redfoot Tortoises". World Chelonian Trust Newsletter, Vol. 3, No. 1
- WEISNER, C. S. and Iben, C. "Influence of Environmental Humidity and Dietary Protein on the Pramidal Growth of Carapaces of African Spurred Tortoises, Geochelone sulcata." Journal of Animal Phys. and Nut., 87-2003.

Some forum threads on this topic include:
- The End of Pyramiding, by Tom
- Pyramiding in Tortoises with MBD, by emysemys

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