Of those, 14 deaths were on United flights, with further nine creatures injured. Across the year, United carried 97,156 animals, meaning there were 2.37 incidents for every 10,000 animals transported during the period.
That was the highest rate seen any US airline, according to the data.
In a statement sent to the BBC, United said: “We were saddened to hear this news. The safety and well-being of all the animals that travel with us is of the utmost importance to United Airlines and our PetSafe team.
“We have been in contact with our customer and have offered assistance. We are reviewing this matter.”
The Sun newspaper reported that Simon was the son of the world’s largest rabbit – a 1.3m-long continental giant rabbit called Darius.
Owner Annette Edwards told the paper: “Simon had a vet’s check-up three hours before the flight and was fit as a fiddle.
“Something very strange has happened and I want to know what. I’ve sent rabbits all around the world and nothing like this has happened before.”
In late March, United was heavily criticised on social media after two girls were reportedly barred from flying for wearing leggings on a flight from Denver to Minneapolis
United said the girls were travelling on a special pass, for employees and their guests, which has a dress code