The death of a dog named Machine on a Delta Air Lines flight prompted an investigation, followed by reinforcement of the airline’s animal transport policies.

Like many travelers, Machine, a bulldog, ran into unexpected problems during a connection in Atlanta.

According to an incident report in the U.S. Department of Transportation’s Air Travel Consumer Report, Machine’s flight from Columbia, S.C., to Atlanta on July 12 was delayed, causing the dog to miss a connecting flight to Dallas-Fort Worth. Machine was transported in a container to a different gate to catch the next flight to Dallas-Fort Worth.

The gate for that flight then changed from B16 to A20. Machine was moved again and the curtain on the container was lifted for ventilation while Machine waited for the flight, the report said.

But when a ramp agent loaded Machine onto the aircraft, he noticed the dog wasn’t moving, according to the report. Machine had died.

“Protecting the animals that fly with Delta is of utmost importance,” Delta spokesman Kent Landers said. “Unfortunately in this incident we relied upon documentation from a vet that didn’t appropriately reflect the dog’s breed.”

The dog’s body was taken to a cargo facility and a veterinary hospital. There, a necropsy found that Machine likely died of struggling resulting in cyanosis — discoloration because of deficient oxygenation of the blood — and collapse. Brachycephalic breeds, which have short or broad heads, are “prone to respiratory compromise due to over exertion” when confined to small places, the necropsy report said.

According to Delta, Machine’s health certificate did not say the dog was a brachycephalic breed, and the certificate indicated the dog could withstand temperatures up to 100 degrees.

An immediate investigation was conducted, according to the incident report. Delta said it redistributed communications to all of its stations on its policy that snub-nosed breeds can’t be transported when the ambient temperature is above 70 degrees, and ground handling agents were advised not to use containers to transport or hold animals while in transit.