WHY COOL HORSES' LEGS AFTER WORK
Studies have shown that core temperature in the flexor tendons of horses can increase to up to 45^ C (38^C is normal) after galloping.
Although laboratory studies show that tendon cells are far more resistant to high temperatures than skin cells, repeated bouts of temperature elevations eventually lead to tendon breakdown.
Tendon tissue blood flow is poor, and cooling the legs both removes the heat elevation, and stimulates blood flow to the area which helps repair any damage.
Horses which jump can also bang their legs, causing bruising and inflamation.
Thus regular cooling of horses' legs serves both to cool the tendons, and to fight general inflammation in the lower limbs.
WHY USE COLD RUNNING WATER
Cold running water provides consistent effective cooling, which is not achieved by other means.
Clay based products act as carriers for volatile substances which evaporate, taking heat with them. But the clay acts as an insulator, counteracting the cooling action. Putting bandages on top exacerbates this, and also prevents the evaporation.
"Arguably, the main benefit of using clay is the necessity to wash it off with a cold hosepipe." Kieren O'Brien MRCVS
Other cooling agents are mostly alcohol based. Alcohol evaporates rapidly at low temperatures, cooling the surface it is associated with, but the effect is short lived and inconsistent.
Experiments have proved that cold water is more effective at cooling tendons than ice.
Cool water boots start cold, and rapidly increase in temperature as they absorb heat from the leg.