my stud dog has lost interest in mating, he jumps on the bitch then jumps off and often ties outside the bitch, has anyone ever had any similar experiences other than this he is fit and healthy

Is it just this bitch.  She could have an imperforate hymen or a condition that causes excesive swelling within the vagina so making it hard or impissible to mate.  It could also be that she isn't ready yet.

You could have your dates wrong and as brainless said she might not be ready