I would wrap both back legs. My hubby is a vet, while he does not do equine anymore, many say he was the best leg man around and he always wraps. He taught me the same. Swelling is bad for a horses legs, the hoof does not expand with the leg causing constricted blood flow, and if you need to see the vet tomorrow for some reason it is much better to have no swelling.
Wash and medicate the wound, put a telfa pad over the cut and wrap. Change bandage tomorrow and wrap again.
I would always err on the side of caution.
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