A baby howler monkey was euthanized at the National Zoo on Sunday night due to complications of metabolic bone disease, the zoo said Tuesday.
The baby, named Loki, had been born March 22 to first-time parents Chula and Pete. Chula was "an exceptional mother," zoo spokesperson Pamela Baker-Masson told NBC Washington.
Keepers noticed Loki was sick on Tuesday, and made their diagnosis after bloodwork and other tests.
Metabolic bone disease is an imbalance of Vitamin D, calcium and phosphorus, most often caused by "lack of sunlight, a lack of dietary intake of vitamin D and/or the body’s inability to properly metabolize these compounds," the zoo said in a release.
The skylights in the Small Mammal House are made of glass that allows UV rays to penetrate the enclosures, the zoo said, but baby howler monkeys can be vulnerable as they begin to wean.
Loki was treated with injectible vitamins, iron and calcium, and was exposed to direct sunlight. She also received a blood transfusion from her, but vets decided to euthanize her Sunday evening due to complications.
"It happens especially at this point in their lives as they're weaning from their mothers and starting to eat solid foods," said Baker-Masson, who said the baby was thriving until then.
The zoo had previously called Loki the first surviving baby howler monkey in the zoo's history. Her parents bred naturally, and Loki was the first baby howler monkey at the National Zoo in years, Baker-Masson said.
Howler monkeys are considered mature at two years.
Initially, Loki was identified as male as keepers remain hands-off and let the mother care for her. She was "bright, alert, and increas[ing her] activity and independence day by day," keepers said shortly after her birth.
"Staff are implementing immediate husbandry changes, where appropriate, such as rotating animals to outdoor enclosures to allow direct sunlight exposure and evaluating diets for at-risk animals," the zoo said in Tuesday's release.