Metabolic Bone Disease in Siamangs
Metabolic bone disease is a condition that affects bone strength. It is well documented in siamangs, small gibbons from Southeast Asia often kept in zoos or wildlife conservation centres. It results from a prolonged imbalance between calciu...
What is it?
Metabolic bone disease is a condition that affects bone strength. It is well documented in siamangs, small gibbons from Southeast Asia often kept in zoos or wildlife conservation centres. It results from a prolonged imbalance between calcium, phosphorus and vitamin D in the diet. The bones gradually become weaker, softer and more prone to fracture. The disease mainly affects young growing animals, but can also occur in adults.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
Early signs are often subtle: the animal moves less, appears stiff or hesitates to jump and climb, even though siamangs are normally very agile in trees.
Limping, cautious gait, reluctance to move around or bear weight on a limb may be observed.
The long bones can become slightly deformed, particularly in the legs, and joint swelling sometimes appears.
In advanced cases, fractures can occur from minor trauma, or even spontaneously.
A young affected animal may show poor growth and general lethargy.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
The main cause is chronic dietary imbalance: insufficient calcium intake, excess phosphorus relative to calcium, or lack of active vitamin D.
The body responds by drawing calcium from the bones to maintain a stable blood level, which gradually weakens them. This is called secondary nutritional hyperparathyroidism.
Lack of exposure to appropriate light (which allows vitamin D synthesis by the skin) can worsen the problem, particularly in animals kept indoors.
Young animals in their growth phase are most vulnerable, as their mineral needs are high.
A diet consisting mainly of fruit, lacking variety or without mineral supplementation, promotes calcium-phosphorus imbalance.
Indoor housing with little or no access to natural light or appropriate lighting increases the risk.
Pregnant or nursing females have increased needs and are therefore also more at risk.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian relies on the animal's feeding history, clinical examination, and especially on X-rays showing reduced bone density, thinning of the cortical bone, or deformities.
Blood tests assess calcium, phosphorus, and sometimes vitamin D levels, as well as parathyroid gland function.
In some cases, further imaging may be recommended to more precisely evaluate the extent of bone lesions.
Treatment
Management is based primarily on gradual dietary correction under veterinary supervision, with calcium and vitamin D supplementation adapted to the individual animal's case.
Rest and limited physical activity are recommended while the bones regain strength, to prevent fractures.
If fractures or significant deformities are present, specific orthopedic management may be necessary.
Pain relief treatment may be used during the recovery phase.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention relies on balanced, varied diet tailored to the siamang's specific needs, ideally established with a veterinarian or a primate nutritionist specialist.
The correct ratio of calcium to phosphorus must be maintained, with adequate vitamin D intake.
Access to natural light or appropriate UV lighting helps vitamin D synthesis in the skin of animals housed indoors.
Regular veterinary checkups allow early detection of any imbalance before clinical signs appear.
Possible complications
Without management, the disease may progress to multiple fractures, permanent bone deformities, and lasting loss of mobility.
Neurological complications are possible if deformities affect the spine and compress the spinal cord.
In severe and prolonged cases, the prognosis may be life-threatening, particularly in young animals.
When to see a veterinarian
The animal limps or avoids using a limb.
It shows unusual reluctance to climb, jump, or move about.
Deformity of a limb or joint swelling is visible.
A fracture is suspected following minor trauma or without apparent cause.
A young animal shows delayed growth or persistent lack of vitality.
Prognosis
The prognosis is favorable if the disease is detected early and diet is corrected promptly: bones can regain strength over time.
However, if the disease is advanced or if major fractures or deformities are already present, permanent impairment of mobility is possible.
Long-term monitoring is still recommended even after improvement.
Frequently asked questions
Is the siamang particularly sensitive to this disease?
Yes, this disorder is frequently reported in gibbons and siamangs kept in captivity, especially when their diet is not sufficiently varied or supplemented with calcium and vitamin D.
Is this disease contagious?
No, it is not an infectious disease. It results from a nutritional imbalance and is not transmitted between animals.
Can a gibbon with a condition be completely cured?
If the disease is managed early, bones can become solid again. However, deformities or fractures that are already established may leave permanent consequences.
How can you prevent this disease in a captive gibbon?
A balanced diet validated by a specialist, adequate intake of calcium and vitamin D, and access to natural light or appropriate lighting are the best preventive measures.
References
AVMA — American Veterinary Medical Association
WSAVA — World Small Animal Veterinary Association
Content reviewed by the TunisieVet editorial team · Updated 02 September 2026
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