my horse walking with hoof abscess pain

My poor horse Red came up lame on Wednesday and is still hurting today (Friday). Is this a hoof abscess? If so, I wish it would rupture and drain so he is not in so much pain. The equine vet put a poultice on it but so far, he is no better. I just took all the wrapping off: that's what the blue stuff is left on his hoof. Poor Red! UPDATE May5th 2011: no abscess ever burst--the lameness lasted about a month and gradually went away. maybe it was knee or shoulder pain? Still a mystery. Anyone else ever seen this extreme lameness that was NOT an abscess?