TWU Local 100 said the carriage horse's cause of death was determined following a necropsy at Cornell University Collage of Veterinary Medicine.

Lady, a 15-year-old horse that had just been brought to New York City from Pennsylvania in June, suffered an aortic rupture likely caused by a small tumor in her adrenal gland, the union said.

On Tuesday, a carriage horse in Manhattan collapsed and died on the way to its stable, according to a local union. Authorities learned of the incident around 2:30 p.m. after receiving a 911 call requesting assistance at the corner of West 51st Street and 11th Avenue in midtown.