Ditto. I’ve heard it was a huge problem for health, sanitation, and just the pure stink of it all! Example…

In late nineteenth century, New York contained somewhere between 150,000 and 200,000 horses. All transport, whether of goods or people, was drawn by horses, from fancy carriages pulled by the finest breeds, to cabs and horse trolleys and countless carts, drays, and wains…

Each horse produced up to 30 pounds of manure per day and a quart of urine. All of this ended up in stables or along the streets. That added up to millions of pounds each day and over 100,000 tons per year (not to mention around 10 million gallons of urine).

By the end of the 19th century, vacant lots around New York City housed manure piles that reached 40 or 60 feet high. It was estimated that in a few decades, every street would have manure piled up to third story levels.

Streets covered by horse manure attracted huge numbers of flies. One estimate claimed that horse manure was the daily hatching ground for three billion disease spreading flies in the United States.

It goes on about the problems of all the horses that were dying in the streets and their carcasses abandoned.