A disposable ice cooling reservoir and an ice boot assembly with the reservoir that is useful for treatment of lameness and stress is described. The reservoir is a bag with closed bottom that is equipped with a one-way fluid valve midway up the bag, and a reinforced rim with fasteners for attaching the reservoir to a separate harness. The bag is available separately, but in use is combined with an orthotic insert, and ankle bootlet and a sole plate. To assemble, the orthotic insert is put into the bottom of the ankle bootlet, which is put into the bottom of the reservoir bag. This partial assembly is then fitted into the sole plate, and reversibly fastened thereto, such as with barbed rivets through the sole plate and the base of the ankle bootlet.