We've all known the problem... Here is my experience and observations after treating half my flock, many of them more than once, for bumblefoot.

I had a flock of 19 chickens - 15 Hyline Browns (AKA Red Sex-Links), and 4 Barred Rocks.
Soon after we moved to the Eastern Shore (of Maryland), I started noticing bumblefoot in my chickens. Two of them had the standard swelled-up foot. The first one was easy, although confusing at first. Pic below:
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AND:
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When I asked where in the world the scab might be, this was suggested by another BYC member:
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Upon washing it deeper, though, I realized that neither of those spots were the scab. I couldn't find a different area, either.
Thus, I left the wound be until I had more info. (Which ended up taking around a month.)
At the end of the month, the wound had progressed. At the tip of the bump (the part on the top of the foot, not the bottom), a red area appeared, and then it turned into a yellowy area. It reminded me of a pimple in many regards - at first no outlet, then a red area, then yellow. (OK, I know, digusting! But, after all, you are reading about BUMBLEFOOT!)



PLEASE NOTE: I AM UNABLE TO COMPLETE ARTICLE AT THIS MOMENT, AND WAS UNABLE TO FIGURE OUT HOW TO REMOVE IT FROM THE ARTICLE LIST SO I COULD CONTINUE EDITING IT AT A LATER TIME. I will try to figure out how to do it. Please be patient. Thanks.