Mating of dogs to produce a healthy litter doesn’t always go to plan. The problem can be from the bitch or the dog’s side but here we are going to discuss the bitch. The scenario can be split into two as there can be firstly a lack of conception and secondly a failure to progress after a successful conception or a smaller litter than expected.

Fertility rates in naturally mated bitches run at around 80% and are dependant on the bitch being mated at the correct time with the most common reason for failure being miss-timing of mating. The bitch’s fertilization period is 2-5 days post ovulation (after the eggs are shed) and unfortunately not all will show appropriate behaviour at the time of greatest fertility and so are not mated appropriately. Sperm may be fertile for up to 7 days inside the female tract after mating although 3-5 days is the average. One study relating signs of pro-oestrus (the first signs of vulval swelling and coloured discharge) and the day of ovulation varied from day 5 to day 30. The peak is around day 12 hence that is the day most people would aim for when mating a bitch. However one can be too late or far too early with some bitches and each cycle may be different in some bitches. This means that testing for ovulation date is important in those bitches who persistently fail to conceive, those that have limited access to the dog or those where the first day of pro-oestrus is unknown.

Other reasons for failure include using an infertile dog, tubal abnormalities (the fallopian tubes which carry the eggs down to the uterus can be blocked), malformed internal development (rare) and infections. Any swab done of a bitch to look for infection must be from the cervix (exit from the uterus) and not the vagina as most bitches carry organisms in the vagina, which are so-called commensals (present normally) and true infections preventing conception are rare. Whilst a bitch is in season the cervix is open to allow sperm to enter and unfortunately, bacteria can enter. Giving antibiotics to a bitch out of season will not make any impact on any infections in the uterus. There are a lot of papers discussing the use of antibiotics in early seasons to try and improve conception rates and most conclude it makes no difference. In most cases, the body will just mop up these bacteria and no problems can occur. More on this later.

However in some cases a full-blown infection can occur resulting in a pyometra. This is a word most breeders dread as it can often result in an emergency hysterectomy and the bitch is lost for breeding. There are medical treatments available but they are risky and success is not guaranteed. The drug used for misalliance aglepristone can be used for the treatment of pyometra although it is not licensed for this. It causes the cervix to relax and expel the uterine contents and may allow a normal pregnancy to occur in the future. The bitch’s owner should monitor her carefully and be aware that neutering may still be necessary if the treatment fails.

The next thing to consider is pregnancy failure. This can occur through resorption or abortion (used here to mean miscarriage and loss of the puppies and not induced by man as the term is used in humans). Early embryonic death can occur when there is a genetic abnormality although the rate and timing when this occurs is not known. If too many eggs are fertilized some may fail to develop due to lack of space in the uterus. The bitch body will break down the unwanted tissue and reabsorb it. Resorption occurs before day 35 and can be confirmed using ultrasound scanning. The earliest that most veterinary surgeons would suggest scanning is day 25-28 but if the ovulation date is known a scan at day 21 can reveal very early signs in some bitches. Since the implantation date is not usually known it is better to be late rather than early to save a false negative result. Spontaneous resorption of 1-2 embryos occurs in up to 10% of embryos. Reasons are not always clear and if a healthy litter results then no investigations would be carried out. However it may be that a whole litter are resorbed or a bitch is confirmed pregnant with multiple foetuses seen by scan and a low litter size results, then an investigation is needed.

Possible causes of resorption are infectious agents and external factors such as stress and drugs. Certain drugs can cause pregnancy failure, steroids such as cortisone and some sedatives may decrease pregnancy viability. Stress is very difficult to quantify as when the body is stressed cortisone is released naturally but it needs a level well above the normal range to cause pregnancy failure. It is unusual to have a high enough level in one burst to cause this. If the bitch was subjected to repeated stressors-pain, environmental change such as re-homing and so on it is possible the additive effect might cause failure and resorption. In a wild state, dogs are said to respond to alpha dominance with a submissive bitch being less likely to conceive as only the alpha will breed. Anecdotally this may occur in a household with a very dominant bitch present.

Lack of progesterone (one of the main pregnancy hormones) is rare although often discussed. Occasionally a pregnancy develops in the body of the uterus (the bitches uterus comprises two horns joined at a “body” which leads to the cervix). Such a pregnancy is not usually viable and after 25-30 days haemorrhage may occur. This can result in the expulsion of the foetus which may allow infection to get into the uterus as the cervix opens. Ultrasound scans will help monitor the other pups for viability.

There are many infectious agents which can cause the failure of pregnancy- the stage of exposure will determine whether resorption or abortion occurs. Some may result in a mixed litter of normal and abnormal puppies.

Bacterial infections include Brucella canis which is currently not found in the UK and this should be considered when importing from other than the UK. Many breeders abroad insist on a clear certificate before allowing visiting bitches and wouldn’t use an untested stud dog. Once affected a dog could never be used for breeding and treatment does not give a good response in dogs or bitches. Other bacteria are numerous and include Escherichia coli, β haemolytic Streptococci, Staphylococcus aureus, and if suspected any aborted foetuses should be taken to the vet for checking (stomach contents can be used for culturing them). Broad-spectrum antibiotics should be used to clear the bitch until the cause is found.

Viral infections are more difficult to treat as antibiotics are ineffective. The major problem is the Canine Herpes Virus (CHV) which produces only a mild cough in adults and is part of the “Kennel cough syndrome” which is so commonly seen in the dog population. One can bring this infection home from anywhere and wouldn’t realise it was any different from the more common Bordatella bronchispetica unless it affects a pregnant bitch. The problems associated with CHV depend on what stage the bitch has reached. Early in pregnancy infection results in foetal death and mummification (foetuses dry up internally) and they are usually expelled. Mid pregnancy infection results in abortion. Late pregnancy results in stillbirths, premature birth and pups which don’t thrive. Puppies can be also affected during birth as the bitch may develop genital nodules which excrete the virus in the fluid. In adults, the disease is self-limiting and no treatment is required but in puppies it is fatal. Bitches that have been affected may produce normal litters later on although there is obviously a risk in keeping such a bitch in case she is a source of infection to others. Males with genital nodules should not be used for breeding.

The other main viral infections which can occur are canine distemper virus, canine parvovirus and canine adenovirus. These are all present in the routine vaccination programmes applied to pups and adults so should not be a problem in breeding bitches. Three yearly vaccination with these main components is now advocated (although as an aside Leptospirosis and Parainfluenza vaccination is still advocated annually until there is knowledge to the contrary). Blood testing for immunity for the former three can be used as a helpful tool for those people concerned about vaccinating, to ensure the bitch has a solid immunity before mating. It is interesting to note that the Guide Dogs recommend vaccinating their breeding bitches at the oestrus cycle when they are not mated. This ensures they don’t have too high an immunity at whelping as a very high level would be passed to puppies. This maternal level can persist in pups and interfere with vaccination regimes. Thus a balance can be achieved between useful immunity and too much.

There is another class of infections are known as protozoal. These include Toxoplasma gondii and Neospora caninum. T. gondii is an uncommon cause of abortion in the bitch but may also cause premature birth, stillbirth and neonatal death. There are also reports of T. gondii causing developmental defects in children whose mothers were exposed during pregnancy, particularly around the head and eyes. The public health consequence of this disease should be considered as it can be transmitted to people and can also cause debility in normal adults and miscarriage (natural abortion) in humans. The disease can be found in stale (over 24 hours old) cat faeces and is shed by sick cats too. The other main potential source is sheep particularly foetal membranes and it is wise to keep pregnant bitches away from fields of sheep around lambing time since membrane and placentas from the sheep may be scattered by vermin and predators. Neospora is another infection that is still considered rare, usually producing neurological signs in the puppies which result in paralysis rather than abortion. However, it is an area currently being closely studied as it does result in abortion in cattle. The only other species known to be affected is the dog at the moment and infection may cross the placenta resulting in infected puppies at birth. Thus pregnant bitches should not be allowed near calving cows as a sensible precaution.

The preceding discussion is not exhaustive but gives a resume of possible reasons for conception and pregnancy failure and some lines to consider if this happens.

Useful books are

• British Small Animal Veterinary Association: Manual of Small Animal Reproduction and Neonatology
• Allen’s Fertility and Obstetrics in the Dog-by Gary C.W. England (a very interesting person to hear talk if you get the chance as he was heavily involved in the Guide Dog breeding programme)