No pregnancy after tie

Question
Just wondering how often it happens that there is no pregnancy after two ties two days in a row. Our Chocolate Lab bred with a lab cross. They had two successful ties, a little short, but definitely tied. The female did not have a pregnancy. Is this common that the breeding doesn't "take" so to speak?  My Choco Lab has successfully sired a little of 9 about six months ago....Should we be concerned about studding him again?

Answer
She may have just been in the wrong stage of her heat cycle. Some females will still stand even if they're not ovulating. Well, it is kind of common. It could be so many different things, bad timing, the bitch may have had a slight infection , or the male could have had an infection. As a stud dog owner, I would recommend taking your boy to the vet for a check up. Just to make sure nothing is amiss with him. If he just sired a litter not too long ago, then I wouldn't think that anything would be wrong with his sperm count. However, he could've picked up an infection from the last female that he was bred to. It may have absolutely nothing to do with him, it may be the female that he was recently bred to. Or, it could just be bad timing. To protect yourself and your dog, I'd take him in for a quick check up. There's just so many different things that could've happened, it's hard to tell across the internet. Have your boy checked. If nothing shows up with him, you may want to talk the bitch owners into having their dog checked out. If nothing shows up on her, they may want to try progesterone testing with her next heat cycle.