I don't know if this is by design or not but I have a cow missing two hooves and a frail back who is pregnant, resulting in a perma-downed state (I only noticed all of this when she collapsed for the third time when early stage pregnant, so hold your horses PETA). Her milk fullness is 100% but apparently she can't be milked. This in itself wouldn't be a problem if it wouldn't cause a cycle through all of my pawns with animal-tending of just standing there one by one trying to initiate a milking job (says so in the error log) and not really doing anything else unless I manually assign something.