We have 4 OSB approx 18 weeks old.  On Friday one of them has gone lame on her back right leg,  she won't put any weight on it.  I have had a close look, felt the leg etc but nothing obvious.  She stays in the arc most of the time but does come out for feed/water and all else so no loss of appetite.  I am calling the vet tomorrow but if anyone has any suggestions on what it might be that would be great,  I am thinking muscle strain maybe.  The pigs are in a large area that (at the moment) is not too muddy.