Having Trouble Walking after Breeding

We have a 9 yr old shitzu that is in heat. Yesterday our 10 month old Austrailian Shepherd got to her. When we found them they were still tied up. Since then our shitzu has been having some trouble controling her back legs. Sometimes she cant keep them under her and they just spread out to the sides. She does not seem to be in any pain at all. She will allow us to touch her anywhere on her legs and hips and we can move and rotate them any direction and she does not seem bothered at all. She is acting normal in all other ways. Any ideas on what could be causing this?

[Aleda M Cheng, D.V.M., C.V.A]

An Australian Shepherd is quite a bit larger than a shitzu!  Your Shitzu would have had to support some of the Shepherd's weight during the mating which may have put a strain on her back and/or hind legs.  Additionally, the "tieing up" due to his larger size could have stretched some of the nerves that innervate her back legs, back, and urinary bladder.  The problem may resolve after several weeks but, she should really be seen by a vet to avoid the potential of long lasting problems.  

There is also a chance that your Shitzu could have become pregnant and should be monitored for this.