Protesters brought the fight to ban horse drawn-carriages to a Manhattan stable Friday.
The group was calling attention to a horse that they said was mistreated.
An Associated Press report says the driver altered a hoof brand to make a sick horse named Caesar appear to be a much younger, healthier horse.
The city is investigating a driver who works out of the stable, but protesters aren't satisfied.
"And we want to know, where is Caesar?" said Edina Birnkrant of Friends of Animals. "This 22-year-old horse in ill health that he lied and worked when he shouldn't have been working, and now he's disappeared."
The Department of Health said the horse has been sold to a farm in Pennsylvania.
The driver could not be reached.
Referring to the city health and consumer affairs departments, a spokeswoman for the carriage industry said, in part, "...We have a robust regulatory system in place with the DOH and DCA, which will determine what violations occurred (if any) and what punishment is deemed necessary."
Mayor Bill de Blasio wants to ban the horses and replace them with motorized vehicles.