[identity profile] steer.livejournal.com 2012-02-20 04:45 pm (UTC)(link)
Well, working horses were routinely slaughtered when they became too old to work anyway. Had a quick look around and according to online sources the average streetcar horse had a life expectancy of only two years anyway so I guess "natural" wastage would just take care of it. "In 1880, New York carted away nearly 15,000 dead equines from its streets, a rate of 41 per day."