Abstract: The welfare of horses in training for racing and competition can be compromised by errors of management of many processes. Lameness is usually identified, as the major problem facing horse trainers and high lameness rates in racehorses is a major welfare concern. Recent epidemiological studies have shed light on important environmental risk factors for lameness and catastrophic incidents during training and racing. Another important threat to the welfare of the athletic horse is failure of appropriate preparation of the horse for competition, resulting in earlier fatigue during a race. Fatigue during racing causes sub-optimal performance, increases the likelihood of injury and, in prolonged exercise contributes to exhaustion and even death. Failure to allow appropriate recovery periods after episodes of training and competition also contributes to a state of chronic fatigue. Trainers recognise that affected horses (or “stale” horses) often have mood disturbances and are reluctant to exercise. Continued excessive training and inadequate recovery (termed, over-training) can result in weight loss and poor performance that is not reversed by short-term recovery periods. In events involving prolonged exercise, the performance and welfare of the horse are compromised by inappropriate fluid balance before and during exercise. Failure to properly prepare and maintain fluid balance of endurance horses results in a severe threat to welfare. Pronounced dehydration and hyperthermia can result in exhaustion and death.