Edit2: Also fish, especially in Nordic countries, where they are given barrels of salted fish as a diet supplement. And rodents, when they get into their feed (frequent source of all kinds of nasty parasites, including some encysted in rodent flesh).
And horses being ridden on polar or mountainous trips were also given meat (salted meat, salted fish, raw seal blubber, etc.), which they were able to subsist on for the duration of the trip.
Also historically many cultures also laced/supplemented horse feed with meat (and blood/fat/etc.) out of some... belief that it will make the horse stronger or more aggressive. Think some Arab countries still give their horses the occasional sheep stew sometimes, and Bhutan still has a thing with giving royal horses (small quantities of) yak meat and tiger fat for some magical mojo or whatnot.
Edit3: Oh and there was also this crazy mare named Lisette belonging to a French officer during the Napoleonic Wars who had a thing for tearing off the faces and fingers of Russian soldiers and eating them. Oh and literally disemboweling one of her grooms, though no eating was involved.
