Horses and mules have had a rough go of it in the labor market, to say nothing of hinnies. American farms employed 26,493,000 equines in 1915. One hundred years later, the number of such animals on the payroll had collapsed to 700,000. (To be fair, the data aren’t great.) Farmers needed horses until tractors and trucks did their work better, so farmers hired millions of them instead. (Again, not great data. The government inexplicably stopped keeping a tally of farm trucks in 2013, though it still counts the number of tractors.)