A New York carriage horse that died en route to work last month was already ill, a post mortem has shown.

The horse, used for taking tourists around Central Park, collapsed and died at around on Sunday 23 October, causing public outcry.

“While the cause of death is still open and is likely to be inconclusive, pending a microscopic analysis of the tissues, the gross necropsy [post mortem] report indicates that he was not a healthy horse,” said a spokesman for the American Society for the Prevention of Cruelty to Animals (ASPCA).

The draft horse, named Charlie and thought to be around 15 years old, was taken to Cornell University College of Veterinary Medicine for examination.

Charlie had been working as a carriage horse for only a few weeks and not much is known about his past.

“We have observed some horses returning to New York City after furloughs [time off] on a farm in worse condition than when they left,” said Dr Pamela Corey, director of equine veterinary services for the ASPCA’s humane law enforcement department.

“We are very concerned that Charlie was forced to work in spite of painful maladies, and these particular health issues can be difficult to diagnose because draft horses are by nature a stoic breed, not displaying signs of pain until they are very severe.”