How would 250 million horses pissing and shitting everywhere, plus needing to be stabled, fed, and used on a daily basis be better? I'd need to see more analys

How would 250 million horses pissing and shitting everywhere, plus needing to be stabled, fed, and used on a daily basis be better? I'd need to see more analysis before I believe that what worked 100 years ago would scale up to what would be needed today without serious problems, environmental and otherwise.