Horses are big animals - but they also vary in size a lot. The figure of 1000 pounds is generally cited as the weight of an average, medium-sized horse.
Draft horses generally weigh between 1,500 and 2,200 pounds, but horses of over 3,000 pounds have been recorded. Meanwhile, miniature horses might weigh as little as 100 pounds and the smallest horse weighs 57 (however, as a dwarf, she should definitely be considered an outlier).
Ponies, of course, weigh less. Either way, except for the freakish minis, they really are big animals and need to be handled accordingly.
This smallish draft horse probably weighs about 1,800 pounds.