Conception problems in the bitch can occur at different stages of the reproductive cycle and have varied causes ranging from behavioural to endocrinological. The most important help to the clinician is to establish the history of the animal, including methods used to monitor ovulation, quality of mating and any subsequent observations the breeder might have made. This will make it easier to direct diagnostics to the right area, resulting in higher success rates and lower costs.
This talk will outline the most common causes for conception problems rather than give a complete overview.
Failure to Show Oestrus at Normal Times
Never Shown Any Oestrus
Females should have started cycling by the time they are 24 months old. In some working dogs this may be a little later if maturation time coincides with intense use and weight loss. Puberty is induced through a combination of age, weight and small amounts of excess body fat. It is important to assess the bitch for any visual clues such as vulva-anal distance (intersexed), stunted growth (hypothyroid) or poor nutritional status.
Have dogs ever shown any interest? If there are periods of heightened attention it will be easiest to see the bitch as soon as this occurs and monitor oestradiol and progesterone. If there are no males or no episodes of any change, an ovarian stimulation test should be performed. Make sure the animal has been in continuous ownership and there is no question of an ovariohysterectomy having been performed. In the author's experience late onset of oestrus in bitches is not detrimental to their later fertility.
Long Inter-Oestrus Periods
Inter-oestrus periods of more than 12 months are considered abnormal. This also makes it very difficult for the breeder, as every season has to be 'used' regardless of suitability of time. The long periods of anoestrus in the bitch are controlled by prolactin, and oestrus can usually be induced with prolactin antagonists such as cabergoline (Galastop). Length of treatment depends on how deep the bitch is in anoestrus, and can take from 2-6 weeks. Only around 80% of bitches will respond and the treatment can be quite costly, depending on the size of animal. However, once pro-oestrus has started it is a normal season with normal fertility.
Short Inter-Oestrus Periods
Short inter-oestrus periods are usually defined as 4 months or less between seasons. These bitches tend to be less fertile as the endometrium does not have enough time to recover. The long-term effect is the frequent exposure to long phases of progesterone after each season, causing cystic endometrial hyperplasia, which in turn reduces fertility.
Inter-oestrus intervals can be extended through the use of progestogens although one should avoid the use of depot preparations in breeding animals as these can suppress oestrus for an unpredictable time.
Failure to Ovulate
Failure to ovulate during the first season is quite common. This is usually followed by a short inter-oestrus period and a normal season. Breeders refer to it as 'split heat'. The first season will not be fertile, as ovulation does not take place.
In older animals seasons can sometimes last for many weeks, and progesterone levels never rise above 2-6 nmol/l. The author found drugs licensed to induce ovulation in dogs did not work. This may be due to the great variation in the time of ovulation (5-28 days from the start of pro-oestrus) and using them too late. The bitch will eventually stop bleeding and the inter-oestrus period is shortened. Many animals will have a normal season after this episode. If the bleeding stops and starts within days follicular cysts may be present. If the animal is not intended for breeding, ovariohysterectomy can be performed as long as progesterone levels are low.
Failure to Conceive Despite Normal Oestrus
Wrong Time of Mating
The wrong time of mating is the most common reason for failure of conception. Breeders have a passion for any equipment or technique that will avoid a visit to the vet, including measurements of electrical resistance in the vagina (Draminski) to the newest fashion of saliva analyses under the microscope. The best way to monitor ovulation is progesterone testing with either in-house enzyme-linked immunosorbent assay (ELISA) kits or laboratory-based results. The canine oddity of ovulating immature oocytes that take 2 days to be ready for fertilisation should be kept in mind. Ovulation can occur any time from 5 to 28 days into the season, although 80% of bitches will ovulate between day 12 and day 15. Sperm survives for up to 7 days in the female reproductive tract.
Failure to Mate 'Properly'
When trying to find causes for an unsuccessful mating it is important to discuss the mating itself. A tie will improve the chances of conception, although so called 'slip matings' can often result in puppies. When a mating has not been achieved the possibility of lack of libido or incompatibility should be discussed. If the dog was very keen and intromission could not be achieved the bitch should be checked for a possible stricture or persistent hymen.
Inexperienced owners in combination with inexperienced dogs can make it difficult to achieve a successful mating.
Brucella canis is the only known venereal disease in the dog and is not present in the UK.
Herpes caninum, although proven to be the cause of neonatal losses, is more difficult to identify as a cause for abortions. It can be transmitted through any dog-to-dog contact and is very difficult to test for. If there is any question about its involvement the vaccination that is now available should be used.
A compromised endometrium or a cervix that remains patent during pregnancy will allow organisms such as Escherichia coli, streptococci and Campylobacter to ascend and invade from the vagina into the uterus and can cause resorptions or abortions. In the author's experience this is not very common. Premating swabs will not give any useful information, as most cultured bacteria are commensals and not pathogens.
Many of the diseases we routinely vaccinate for (distemper, parvovirus, leptospirosis, canine adenovirus) can cause resorption or abortions.
Resorption may occur in the first 35 days of pregnancy. It is more common for a few embryos/ foetuses to be absorbed rather than a whole litter. Resorption should only be taken into consideration if a pregnancy had previously been confirmed through ultrasound examination or relaxin testing. Around 30-35 days post mating there are changes in the bitch that make it more obvious whether they are pregnant or not, and are often interpreted by breeders as resorption.
Age of the Bitch
Pregnancy is most easily achieved in young adulthood. In bitches the quality of the endometrium deteriorates with every season that they are not pregnant and so the combination of the number of pregnancies and age should be taken into consideration. A bitch that is 5 years old and has never had a litter is less likely to conceive than a bitch of the same age with two litters. In working dogs or show animals the 'right time' can easily be missed due to other commitments. The same applies to the male dog and the combined age of the animals should be kept as low as possible. In case of an older bitch a young proven dog should be used.
Hypoluteinism as a cause of resorptions in some breeds such as the German Shepherd Dog and Old English Sheepdog has been reported. It is important to measure progesterone levels before supplementing.
Dogs are generally very fertile when proper monitoring of ovulation takes place and both the bitch and the dog are reasonably young and healthy. The veterinary surgeon can help breeders by basing their decisions on sound results and professional advice, rather than dubious sales pitches and old wives' tales. It is important to insist on the necessary costs, such as progesterone testing, and avoid the unnecessary costs, such as routine swabs, to build up a relationship with breeders. There is no grey area in conception: either the bitch is pregnant or not and the success of the effort and time spent will be measured on the outcome alone.