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WASHINGTON, D.C. (WUSA) - Loki, a young black howler monkey, was euthanized Sunday after suffering complications from metabolic bone disease, the National Zoo has announced.

Loki, born in March, had been treated with injectible vitamins, iron, calcium, and was exposed to direct sunlightwhile receiving around-the-clock nursing care. The disease is a vitamin D, calcium and phosphorus imbalance,most often caused by lack of sunlight (ultraviolet light), lack ofdietary intake of vitamin D and/or the body's inability to properlymetabolize these compounds.

A blood transfusion wasprovided to Loki from her father, Pele, as well. Despite the combined efforts ofkeepers, nutritionists, technicians and veterinarians, Loki continued to grow weaker and on Sunday morning, the consensus decision was made to humanely euthanize Loki.

The skylights in the Zoo's Small Mammal House are made of UV-transmissible glass, which allows the UV to penetrate the animal enclosures, providing sunlight. This is important for young animals especially as they wean. Loki had been in the weaning process, as she was raised entirely by her dam, Chula, and was just beginning to eat solid foods. Because the amount of UV light penetration can vary depending on many factors, staff regularly use light meters to measure the intensity of the UV light.

Zoo experts are now examining the accuracy of the light meters used and the staff is also implementing immediate changes, including rotating animals to outdoor enclosures for direct sunlight exposure, and evaluating diets for at-risk animals.

Loki was born on March 22 to first-time parents Chula and Pele. Two pairs of howler monkeys are on exhibit at the Zoo.