Photo by Mike Crosby for the National Zoo

Sad news from the National Zoo—a howler monkey born in March died over the weekend:

The Smithsonian’s National Zoo euthanized a young black howler monkey, Loki, Sunday, Oct. 7, because she was ill from complications of metabolic bone disease. This disease is a vitamin D, calcium and phosphorus imbalance. It is most often caused by lack of sunlight (ultraviolet light), lack of dietary intake of vitamin D and/or the body’s inability to properly metabolize these compounds.

For five days, Loki was treated in the hospital with injectable vitamins, iron, calcium and exposed to direct sunlight while receiving around-the-clock nursing care. A blood transfusion was provided from the father as well. Despite the combined efforts of keepers, nutritionists, technicians and veterinarians, the monkey grew weaker. The consensus decision was made to humanely euthanize Loki on Sunday morning.

Loki was the name given to the howler monkey—the first born at the zoo—by a majority of voters on Facebook earlier this year.