Research has been shown that spraying cold tap water over a horse's body, except its head, resulted in a more rapid decrease in heart rate. Rectal and pulmonary artery temperatures also declined faster with active cooling. There was no indication of negative physical or biochemical effects of the more active, rapid cooling of the bodies of hot horses. It also reduces the oxygen needs for intense performance. Horses not warmed-up before performance produce more lactic acid which is associated with fatigue.
Transportation is stressful on horses.
Horses may lose 3 percent of their body weight during transportation in hot, humid conditions, since they may not drink, even when water is available. However, they will recover this weight loss if properly watered after transportation. Performance can be less than desirable soon after a long, hot ride in a trailer or van due to water and electrolyte balance. Transport horses early, late or at night when it is cooler in summer. Trailers and vans should be properly vented.