Race horses are trained to switch leads either by a shift in the jockey's body weight or by a tap of the jockey whip. This is done to help reduce fatigue and increase efficiency. In this country, horses run to the left through a turn, and for increased efficiency, you want a horse to be on the left lead going through the turn. They may run on the right lead on the straightaways; however, as a horse moves through the pack and may need to move to the left or right, it certainly will be more efficient to be on the correct lead. They may be bumped or crowded and forced off the desired lead and need to be placed back on the desired lead. This applies to races of longer length. Horses racing shorter distances where a turn is not involved may run the entire race on the same lead.