Metabolic Bone Disease in Orangutans

What is it?

Metabolic bone disease is a condition that affects bone strength. It develops when the balance between calcium, phosphorus, and vitamin D becomes disrupted over an extended period. In Bornean orangutans, this disease is primarily observed in captivity, particularly in growing juveniles or in individuals fed an unbalanced diet. The bones gradually become more fragile, less dense, and are more prone to deformation or fracture than normal.\n\nThis disease typically progresses slowly, which makes it difficult to detect in its early stages. It requires specialized veterinary care, as it affects a protected and vulnerable animal.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Causes and risk factors

The primary cause is prolonged dietary imbalance, particularly a lack of calcium, excess phosphorus, or vitamin D deficiency. This vitamin is essential as it allows the body to absorb calcium properly from food. In captive orangutans, inadequate exposure to appropriate light can worsen the problem, since vitamin D is partly synthesized by the skin under the influence of certain light wavelengths.\n\nA diet too high in certain fruits or too low in calcium-containing products can also contribute to the imbalance. The condition typically develops gradually over several months, rather than appearing suddenly.

Growing juveniles are more vulnerable, as their calcium and vitamin D requirements are higher. Animals living in enclosures with limited access to appropriate light are also at greater risk. Feeding not supervised by an animal nutrition specialist, or a monotonous diet, increases the likelihood of imbalance. Pregnant or nursing females may have elevated nutritional needs which, if not met, favor the development of the disease.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

Treatment

Management is based primarily on a gradual correction of the diet, under specialist supervision, with appropriate calcium and vitamin D intake. Controlled exposure to appropriate lighting can be introduced. In some cases, targeted nutritional supplements are used. If fracture or severe deformity is present, orthopaedic surgery may be considered. Rest and environmental adjustment to limit intense physical exertion form part of the management while bones are healing.

Prevention

Possible complications

Without treatment, the disease may progress to spontaneous fractures, permanent deformities of the limbs or spine, and lasting loss of mobility. In young animals, delayed bone growth may have long-term effects on posture and locomotion.

When to see a veterinarian

Prognosis

The prognosis depends largely on how early treatment is started. When detected early, the disease typically responds well to dietary correction and the outlook is favourable. If diagnosis is delayed, with deformities or multiple fractures already present, lasting damage may result and permanently affect the animal's quality of life and mobility.

Frequently asked questions

References

WOAH — Organisation mondiale de la santé animale (ex-OIE)

AAFP — American Association of Feline Practitioners

Content reviewed by the TunisieVet editorial team · Updated 29 August 2026