What are you trying to achieve when cooling horses legs? Decreasing temperatures such that they could have an anti-inflammatory effect internally OR bring down leg temperatures to the normal temperature (37-38°C) which a horse is designed to do of its own accord?
A study was completed to look at heat removed after 30 mins from a phantom leg. A phantom leg was used so each test was repeatable as many variables exist when using a live subject. Cryochaps removed significantly more heat than water cooling boots or clay, see graph below:

Marlin, D.J. (April 09, 2019) Evaluation of the COOLING EFFICACY OF DIFFERENT EQUINE LEG COOLING METHODS Comparative Exercise Physiology.
#CRYOCHAPS #NoLegNoHorse #MakeLegsLastLonger