Metabolic Bone Disease

The
term ‘Metabolic Bone Disease
(or ‘Disorder’) is not an actual disease,
but a catch-term for a wide variety of things that can soften or deform
a tortoise’s shell and skeleton. Some MBD’s are due to disease
processes, like ‘Fibrous osteodystrophy’, ‘Hypertropic osteopathy’,
‘Paget’s Disease’, etc. Most
MBD’s are due to problems with diet and
basic cares. The most common is ‘Nutritional
Secondary
Hyperparathyroidism

or NSHP. Common names for this condition are
‘rubber jaw’ in lizards, or ‘soft shell’ in turtles and tortoises. The
root cause is usually a combination of too little calcium, too much
phosphorous, or too little vitamin D, but can also be aggravated by
poor temps, poor hydration, etc. Pyramiding is usually a form or
symptom of NSHP as well. [Mader]

Prevention

Since
NSHP
is almost entirely due to problems in basic husbandry (mostly diet, but
also cares, housing, etc.), it can be prevented
by providing the tortoise with the right diet and husbandry, appropriate
to the species. We
may need to supplement
key elements
– especially calcium, vitamin D,
fiber, iron, etc., or work to augment the temps, lighting, humidity,
and so forth.

Tortoises
are very flexible when hatched, and need a diet and cares designed to
promote shell and skeleton development from the very beginning. If the
shell does not ‘firm up’ in a timely fashion, various forms of NSHP and
pyramiding (see right) will develop.

Symptoms
NSHP
shows
up in tortoises as a softened, leathery, or rubbery shell*, but
by the time the shell shows obvious problems, there may be problems in
the bones. Things like pyramided or raised scutes, deformed jaws, weak
and/or deformed limbs,
splayed walking, dragging limbs, paralysis, and cloacal prolapses are
signs
something is wrong.  (* Note: Some turtles and tortoises
are supposed to have soft, leathery, or rubbery shells such as the
Pancake Tortoise and Soft-shell Turtles.)

IMPORTANT- Very young
tortoises
are a bit soft or flexible so they can fit in the egg and so the shell
can move as they grow. This often worries keepers, but there is a
difference between a young shell and a soft shell. Young tortoise
shells are springy, like they are made of a stiff plastic- the plastron
may feel a bit springy for some time. Soft shells, however, feel more
‘leathery’ and do not resist being compressed as much. If the shell
just gets softer instead of firming up, you should take action.

Treatment
As
long as the tortoise is still eating, the shell is not too soft, and
there are no other worrisome symptoms, the tortoise can probably be
treated at home. Do not, however, suddenly start dumping lots of
calcium in the poor animal or flooding it with UVB lighting. Try…

  1. Double
    check
    your housing, lighting, diet, and so forth. It is often helpful
    to ask for a second opinion from an experienced keeper. Try the various pages on this site or those listed in the Helpful Links.
  2. Find
    a way to offer unfiltered sunlight or UVB lighting.
  3. Increase high calcium foods, like
    collard or turnip greens, grape or mulberry leaves, cactus pads, etc.
  4. Add
    a little fine calcium powder
    to meals that are ‘iffy’ in calcium. Calcium tastes bitter, so do not
    use much!
  5. Offer soaks if it is
    dehydrated or not eating.


If the shell is very soft; the
tortoise is not
eating; is showing other symptoms; or is not responding to your cares,
you should see a vet. The vet should do blood and other tests, an
x-ray, and take a complete history to try to determine if the problem
is NSHP or another bone problem. The vet would then determine a course
of treatment based on the findings. NSHP is usually treated with
vitamin D3 injections and supplemental calcium orally, then follow-ups
over two weeks. More severe cases may also need dietary support and
other treatment. It is important to follow the vets suggestions as
carefully as possible for the best chance at recovery.


Outcome
Treated
properly, the tortoise should recover fully, although some shell
or skeletal deformity will remain, and there may be residual muscle or
nerve problems. The earlier it is caught, the better the chances for a
complete recovery.


Untreated NSHP can be fatal, so make sure the
tortoise gets the right cares.

Pyramiding
When
scutes grow in a conical or piled-up fashion with the bone deforming
behind the scutes, we call it ‘pyramiding’. Some tortoises, such as Star
Tortoises, pyramid naturally, and some tortoises, such as some
Testudo
species, seem a little more resistant to the problem. As common as the
condition is in captive tortoises like Sulcata, Leopards, and
Red-foots, there is very little hard research on it. See also Mike Pingleton’s article on pyramiding, reprinted in the Library.


Causes:
Pyramiding
has been blamed in the past on excess protein in the diet, but since the
shell underneath is
also
pyramided, it is clearly a form of MBD, so the causes are the same as
that. Experiments have shown that keeping a
growing tortoise’s shell misted throughout the day helps prevent
pyramiding [Fife,
Weisner, etc.], but a counter-argument is that this causes thinner
scutes and does not address the shell issues beneath the scutes-
pyramided shell and spongy bones with a lower than usual density.
[Highfield
2010]


The most likely root cause is a disruption of the natural diet and cycles. Wild tortoises generally go through seasonal changes that affect what kind and how much food is available, and the shell grows in response which gives all the different kinds of tissues the chance to ‘catch up’.

Prevention:
This would
be the same as the prevention of MBD as well as trying to offer naturalistic climate and diets.


Signals:
The
first
signals of pyramiding may be thick growth rings or a deepening
grove between the scutes instead of the normal smooth growth.
Additional new growth will add more height to the previous layers if
things are not corrected and grooves or valleys will start to develop
between scutes. While pyramiding usually happens early, it can start to
develop later in some species (like Red-foots) if conditions allow.


Treatment:
There
is no way to eliminate pyramids once they start. Treatment focuses on
preventing further pyramiding by doing those things that prevent
pyramiding. If things are corrected, new growth will be reasonably
flat- although it may take years to see a significant difference. 


Outcome:
Pyramiding
by
itself is mostly a cosmetic issue and should not, by itself, be
considered a sign of failure. Pyramided tortoises live as long and
successful a life as those without pyramids.
However– because it represents a
flaw in our cares or understandings, we want to continue to learn more
about it and work to prevent it.

Resources

Edited 8-15-2012 (C) Mark Adkins

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