Hypothesis 1:  Trauma
The foal is lame in the right rear fetlock region.  The owner thinks that the mare may 
have stepped on the foal.  If this is the case, there may be varying states of tissue or bone 
damage inflicted by this type of injury.  There may be a fracture of the bone in this area 
of the hind limb. This could cause the lameness and swelling that the foal is experiencing.  
Or, if the trauma inflicted wasnÕt as severe, there may only be soft tissue swelling and 
bruising.  This too can also account for the lameness and swelling if this type of injury is 
severe enough.  Radiographs, and possibly ultrasound, need to be done in order to rule 
out fracture or soft tissue swelling due to trauma.