I bred my 4 year old bitch 8 weeks ago. I bred her to the same dog she had a litter to about a year and a half ago and she produced 8 healthy pups with no problems. This time round she was mateed to the same dog and they tied several times over the correct days and when she was receptive to him and standing still moving her tail to the side etc.
She has shown no sign of being in pup, her teats are not down and she has not gained any weight despite extra feeding. What do you think is most likely to be the cause? the bitch not releasing any eggs or the dogs sperm not being fertile? Or maybe a combination of both?
I did everything by the book but it looks like she is barren this time round, both dogs are healthy and in good condition not overweight or underweight and the stud dog has not been over used. Any ideas what went wrong this time?

some bitches will stand and appear receptive for 10 days in a season, yet they are still only fertile for a couple of days.  So you may not have got the right days.  Also, just because a bitch ovulates on day 12 for example one season doesn't mean she will do it on every season.  She may not have ovulated this time until 4 or 5 days after the mating.  The easiest bitches to know when to mate are those that only stand for 2 or 3 days in a season.

I would guess that neither she nor the stud dog are infertile.  It is more likely that you got the wrong day.  However, it may be worth getting the stud dog owner to either have his dog swabbed for an infection or put on a course of antibiotics that cover the most likely infections.  And of course you should do the same with your bitch when she comes in season next time, before you try again.