[Lady of Yorkies]

I have a male that I haven't used until a few months ago. He is one of my puppies that I never sold. I haven't used him because his father is my breeder. He is over 2 years old now and has a most wonderous coat. I wanted to breed him to see if his coat could be passed on. I chose a female who also has a nice coat. I never saw them tie but I had them in the cage together the whole time so they could have tied when I wasn't watching. No puppies were born. The female didn't get pregnant.

Is it possible that he doesn't know how to do it? I saw them trying to tie but like I said, they didn't tie in front of me. Sylvia