
I had just one who, after a couple of good matings, went into a more blood-coloured discharge to the end of her season. None of mine had done this before, mated or not - they just gradually had less and less discharge, which wasn't blood-coloured, until 21 + days when it was all over. She had an uneventful pregnancy and 9 super puppies at the end of it.
If you are worried about your girl, have your vet take a look. Any strange discharge early in a pregnancy would worry me.
ps We did have one AI'd over in Canada (actually in the States) after the stud dog would have nothing to do with her and having travelled from Toronto to just outside Philly, I didn't want to come home with 'nothing'. Her pregnancy was uneventful too. Some breeders back here want a bitch to be on Synulox just before being mated (and on through the course) but my vet always said why? If she's healthy at the time of mating, she should be fine. Some stud owners just prefer to have this done however, especially if they have a popular stud dog, I suppose.