Welcome to YorkieTalk. I have always had my females spayed, but that is because I worried about pyrometra and mammary tumors. The more I have read because of YT, I think I would explore tubal ligation more if it was possible in the future. I strongly believe that it is best to wait until after the first heat after reading a lot about this subject.
http://www.caninesports.com/uploads/...tions_2013.pdf