Why is it important?
Also known as a misalliance or mismating. Even with the very best of intentions, sometimes it happens - a randy dog manages to catch your bitch when she's in season and before you can stop them, he's had his wicked way with her. Fifty years ago, the only solution was to wait it out and hope no puppies emerged (and if they did, that you could find homes for them), but nowadays there are a lot more options.
Can I keep the puppies?
Before you make a decision, you need to think long and hard about what you want to do. While raising a litter of puppies can be very rewarding, it is also very expensive, very hard work, and with thousands of unwanted dogs in rescue centres, you need to be certain you can find "forever homes" for all of them. If you don;t know who the father is, there's also the minor issue that the pups won't be eligible for any pedigree books, which will affect their financial value.
What are the chances that my bitch is in pup after a single mating?
Pretty good, we're sorry to say. In dogs, a bitch will not allow herself to be mated unless she's in oestrus and therefore probably fertile. No matter how enthusiastic the dog is, if she's not ready he doesn't get a chance. So, she will be in the fertile phase of her cycle. If the dog ties (his penis becomes trapped inside the bitch after mating), the probability is fairly high that some puppies will result. However, untied matings may also be fertile - most dogs won't ejaculate fully until they've tied, but it only takes a handful of sperm to give you a litter!
When can you test for pregnancy?
There are several different tests available for pregnancy in bitches:
(1) Abdominal palpation
In this test, the vet will carefully feel the abdomen and try to locate the bulges in the uterus that contain the developing puppies. This is most reliable between 4 and 5 weeks after the mating, but is very tricky in larger bitches and any who are overweight. Nowadays, we wouldn't routinely recommend this method, because it's not terribly reliable - it's very easy to miss a small puppy, or find a big lump of faeces and think it is a pup!
(2) Relaxin Blood Test
This is a blood test for the hormone relaxin which is produced by the developing placenta. It is a pretty reliable way to determine whether the bitch is genuinely pregnant, or just has a false pregnancy. In some pregnant bitches, the test will give a positive result at 22 days after mating - however, a negative result this early may simply mean the puppies aren't developed enough yet, so it should be repeated 10-14 days later. It also doesn't tell you whether the puppies are alive or not.
(3) Ultrasound scan
This is the method we prefer to use - it is accurate from about 3 ½ weeks after mating, and can tell you how healthy the puppies are. It cannot, however, tell you how many there are - you'll need to wait until the puppies' skeletons form (in the last 3 weeks) and then get an X-ray to count noses to know that.
Spay her. If you don't intend to breed from your bitch again, your vets can spay her even if she is in pup - although it is a more difficult and risky procedure, because the blood supply to the uterus is much bigger. It is not something we would routinely recommend, but there may be some situations when it is appropriate.
Use medical treatment to cause her to reabsorb or abort the litter. This is usually the treatment of choice. Vets generally use a drug called aglepristone, which blocks the action of progesterone (the "pregnancy hormone"), causing the bitch to reabsorb the embryos (if given early enough in pregnancy). It takes the form of two injections 24 hours apart, given any time from 10 to 45 days after mating, and is effective in over 90% of cases. Occasionally, one or two of the puppies survive, so it is always useful to get a scan done 10 days afterwards, just to make sure.
If you think your bitch might have been "caught" - give your vet a ring and ask for advice!