No, horses developed from an herbivorous ancestor. They were never carnivores as they have no canine teeth. Nevertheless, there are some reports from the history of meat eating horses.
During the years of active exploring new continents, sled dogs were a common way to travel to the South pole. However, some explorers were also using horses. These horses were given meat and fat to eat as there was no grass there to feed them and hay would have taken too much space to carry to the expedition.
The American gelding known as "Freight Train" was reported to have been hunting, killing and consuming small birds in the 50's. He also attacked people a number of times.
Another gruesome report is about the Russian officer, that was killed and eaten by a French mare Lisette during the Napoleonic Campaign.
Nowadays, in Iceland horses are given salted fish as a protein and mineral/salt supplement. This is known as 'torshátur' and is commonly used in the winter months when the pasture is covered with snow and the horses have to spend most of their time indoors.