Ian Wood explains
Do horses know when they have won?
Horses do not understand “winning” in the same way that humans do. They have no concept of race results, prize money or competition in the abstract sense.
However, they do respond to what follows a race. After a particularly good performance, a horse may experience encouragement from the jockey, attention from handlers and a more positive atmosphere. Over time, some horses may associate this with a favourable experience.
Certain horses also appear more competitive in the closing stages of a race, while others respond less willingly. Ultimately, their performance is driven by instinct, training, physical ability, temperament and their response to pressure—not by an understanding of winning itself.