Keepers say they do not fully understand why Zuri, 12, attacked the 10-year-old male

A lioness killed the father of her three cubs at the Indianapolis zoo, suffocating her longtime mate by locking her jaws on his neck.

Zoo officials were at a loss to explain the attack by Zuri, a 12-year-old female African lion, on her 10-year-old mate, Nyack.

The lions had been held together for eight years and had three cubs in 2015, the zoo said in a statement. Zookeepers had never before noticed any aggression between the pair.

Staff rushed to the lions’ enclosure after hearing an “unusual amount of roaring” and found Zuri in a fierce fight with the father of her cubs.

“She had Nyack by the neck,” said the zoo’s curator David Hagan. “Keepers came up and saw what was occurring and made an attempt to separate the two. But she continued to hang on to Nyack by the neck until he stopped moving.”

Zoo staff were devastated by the death and may never fully understand what happened, Hagan said. “They build strong bonds with the animals so any loss affects us all greatly. For a lot of us, it’s just like a family member,” he said.

Facebook Twitter Pinterest Zoo staff have been left devastated by the death of Nyack. Photograph: Reuters

An autopsy found Nyack died of suffocation from injuries to the neck. One of the couple’s offspring, a three-year-old female named Sukari, was in the outdoor lion pen at the time and was not hurt.

Nyack and Zuri’s two male cubs are kept in a separate part of the exhibit, having been separated earlier this year at the age when male lions reach young adulthood and typically leave the pride.

“We will conduct a thorough review to attempt to understand what may have led to this,” the zoo wrote on its Facebook page. “Zuri and the other three lions are all OK. Nyack was a magnificent lion and he will be greatly missed. We appreciate the support from our community as we cope with the loss.”

The lioness was on loan from San Diego zoo as part of the species survival plan managed by the Association of Zoos and Aquariums. There were no immediate plans to change how the lions are managed, the zoo said.

The zoo described Zuri on its website as an “attentive and protective mother”, usually found “keeping an eye on her three cubs”. She weighs about 325lbs, 25lbs less than her mate.

Nyack was described as a “very vocal and laid-back” lion with a large mane, a fan of spices and playing with boomer balls. “He can often be heard roaring on exhibit,” the zoo wrote.