The art of breeding dogs can certainly be challenging at times and there is more and more research into this area as a result. Breeding difficulties can be the result of many different issues and this article will explore some these including the time of mating, ovulation problems, infectious diseases and how ultrasound can be used to detect early changes.
In comparison to the last 10 to 20 years, veterinarians are now more frequently asked to help optimise reproduction in dogs. This is mainly due to the increased popularity of purebred dogs as well as for sentimental or financial reasons. However, breeders may be more concerned about different kinds of breeding problems that include, but not limited to, infertility (their bitches produce no pups after mating or artificial insemination), anoestrus, or a low prolificacy rate.
Many different issues can lead to low fertility, including hormonal problems, infectious diseases, and congenital or acquired defects of the genital tract. Unfortunately, few techniques exist which can be utilised in the investigation of the reproductive functions in bitches.
Interestingly, most bitches cannot be simply classified as fertile or infertile. Such a definite classification would be too simple, and many bitches may just be “hypo-fertile”. Several factors can act together causing the bitch to be infertile at a certain period of time. As in humans, the cause of infertility is rarely due exclusively to the male part or the female part.
In the bitch, things become even more difficult when we realise that apparent infertility can be due to very different problems that are often very difficult to distinguish. For example, lack of fertilisation (no union between eggs and sperm) and early embryonic death.
A study has shown that embryonic resorption is not uncommon in the bitch (England and Russo 2004). In this study, 20 pregnant labrador bitches were followed and 10.6% (14/132) of embryos resorbed before day 35. Therefore, when investigating a fertility problem, veterinarians must check precisely not just the ovulation period but also the early gestational phase.
1. Optimising the Time of Mating and Detecting Ovulation Problems
According to the vast majority of scientific publications, mistimed breeding represents by far the most common cause of infertility in the bitch. The incidence rate however, may vary between 40% and 80% of infertile bitches.
Although the following belief has been clearly proved erroneous in approximately 30% of bitches, many breeders are still convinced that a bitch will conceive when mated around the 12th day of the heat period. Actually, it has been clearly demonstrated that a bitch may ovulate as early as the 3rd or 4th day after the onset of pro-oestrus and as late as the 30th day of the heat period.
Nowadays, there are numerous techniques available that may be utilised to investigate the “optimal time for breeding”: vaginal cytology, endoscopic appearance of vaginal folds and progesterone assays are the most commonly used methods. Ovarian ultrasonography is especially useful for infertile bitches, as it represents the most accurate way to determine the precise date of ovulation. This method also helps quantify the number of growing follicules as well as which follicules undergo ovulation and as such, ultrasonography helps to evaluate the fertility potential of the bitch.
Other causes of infertility exist. As often ascertained in large animals (such as horses and cows), it is important that veterinarians first consider if infertile bitches show regular inter-oestrus intervals or irregular ovarian cycles. Anovulatory cycles are not common in the bitch. In such anovulatory cycles, serum progesterone levels never increase above 3.5 to 6 ng/ml.
Many infectious agents have been suspected to induce infertility in the bitch,, however, very few studies have been conducted in this field. It is generally thought that the incidence of infectious causes of canine infertility is greater in larger breeding kennels than in small family breeding kennels or in pet dogs.
Infectious diseases could promote infertility in various pathogenic ways. In the vagina, infection may have a spermicidal effect, interfere with sperm motility by causing ciliostasis, for example, or facilitate the penetration of infectious agents into the uterus during proestrus and oestrus.
Uterine infection leads to lymphogenic infiltration of the uterine wall, creating a hostile environment for the sperm and eggs, and can cause interference with the development of the zygote or even cause early embryonic death.
uring later stages of pregnancy, endometritis and/or placentitis, or placental infection may occur, leading to fetal resorption. Endometritis is a common cause of infertility in mares. In bitches, however, it is hard to diagnose. Bitches with cystic endometrial hyperplasia (CEH) are often infertile due to implantation failure after conception.
2. Optimising the Detection of Problems During Pregnancy.
It is important not to limit the investigation to the oestrous stage but also to monitor bitches during the entire pregnancy stage. Nowadays, ultrasonography provides a great tool, helping to diagnose early embryonic resorption, uterine problems and fetal developmental problems. It also helps to estimate the stage of pregnancy (foetal measurements or foetometry) and even to the sex of foetuses.
Bitches may also suffer from hypoluteoidism, which is the lack of progesterone secretion during the early stages of pregnancy and is crucial for embryonic retention. Some breeds are more predisposed to express hypoluteoidism, such as Rottweilers and German Shepherds. We have also identified this condition in many giant breeds of dog.
3. Optimising Parturition
Nowadays the date of parturition can be estimated quite precisely using hormonal and clinical tests. It is a way for breeders to ensure they are ready and available at the right time.
The use of ultrasound may help to diagnose early foetal hypoxia. In some of these cases, parturition may be induced or caesarean sections may be planned in advance.
Last but not least, the techniques of neonatal resuscitation are better known and may help breeders save neonatal puppies that would have died in the past.