The cause of death of a carriage horse that collapsed and died in Hell's Kitchen Tuesday has been determined, the union representing carriage horse operators said Friday.  Lady, a 15-year-old horse that had just been brought to New York City from Pennsylvania in June,

The horse, named Lady, crumpled to the ground in Hell's Kitchen after she had only done two rides Tuesday afternoon — stoking renewed outrage from animal rights activists.

The 15-year-old Standardbred cross horse died due to a small tumor in her adrenal gland that likely caused an aortic rupture, a necropsy found, a TWU representative said.