Mating and fertility

© Therese Rodin


Background: The pheromones, the scents that among other things provide sexual signals, are built up by genes that are part of the immune system, which carry the individual’s “genetic ID code”. Therefore, a bitch can sense from a male’s scent how well he fits in with her genetic code. The dogs that are least related are best suited to each other. In addition to the ethical aspect, the bitch’s ability to choose the best partner is a crucial reason for the mating to take place naturally and without coercion from humans. It is beneficial for the genetic diversity to give the bitch the right to decline a male (Sundgren 2004; Selin 2017). As breeders, we then have to find another male that the bitch accepts.

A major problem in dog breeding up to today is the phenomenon of the “popular sire syndrome”. This means that single, popular males are used in breeding sometimes hundreds of times, with the result that hundreds of dogs within a breed are half siblings. Cassie Smith has done a survey of a so-called popular male in the English bulldog breeding in the UK and she has also looked at how many litters the English bulldogs got which became “best of breed” at Crufts 2010–2018.

The example of the “popular sire” born in 1980 shows that he had over 20,000 descendants 20 years after he was born. The image below with the Crufts winners shows six males and two bitches. The bitches received two litters respectively while the males received 106, 13, 66, 127 and 51 litters each. (A male was registered in Spain, and for him there was no data on the number of litters.)

Graphics: Cassie Smith
Graphics: Cassie Smith

The tendency to overuse popular males in breeding is also a problem in Pug breeding, where a few males are used as studs while the others are not used in breeding at all (see e.g. Calboli et al. 2008, Supplemental, 4). It is a problem that so few dogs are part of the effective breeding population; a few dogs are selected as “breeding dogs”, while the genes of the rest of the population are lost. Thus, this way of breeding, results in great loss of alleles, i.e. varieties of genes. Each dog carries a unique set of alleles and the fewer dogs that are used in breeding the greater the loss of alleles in a breed. It also leads faster to higher inbreeding rates because the breeding population is small and thus all dogs more quickly become related to each other (Selin 2017; Beuchat 2018).

We therefore need to ensure that as many Pugs as possible are used in breeding although at the same time we have quite large health problems within the breed. There are no perfect dogs. What we have to do is to set up breeding goals that are absolute requirements in the selection of breeding dogs and those requirements should include dogs that are “good enough” and not only the top dogs. Of course, the breeding goals must be in line with the country’s laws and regulations.

If the conformation of the dog breed is close to the “normal dog” and has a low inbreeding coefficient then only perhaps one or a couple of goals are needed. For the Pug, extensive work is required in terms of both conformation and inbreeding percentage. To succeed, however, we need to keep the goals as few as possible. We recommend that the following is the highest priority: BOAS, PDE, DM and genetic diversity. The Pugs that are used in breeding should have maximum BOAS I and carriers of the PDE marker and/or the DM gene should be paired with dogs that are free. Through the choice of a suitable donor breed, genetic diversity is created, which will create much greater opportunities for reaching the goal of BOAS-free Pugs. When the Pugs become BOAS-free, the skull will be less brachycephalic and eyes and teeth will improve by themselves. The donor breed will also contribute with a less compact body, which seems to lead to the disappearance of vertebral anomalies. Likewise, a leaner, lighter and less sturdy Pug will lead to a decrease of hips problems.

Goal: The Pug has a natural mating behavior, which shall last. The genetic diversity is to be increased by using more Pugs that are “good enough” in breeding. Especially more males need to be used.

Strategy: The bitch shall have the right to “say no”, i.e. decline a mating. The first time a bitch gets pregnant, it should be through natural mating. If it is considered very valuable to combine a bitch with a male that is abroad, the second or third mating can be done by insemination.

If the bitch is in shape and everything looks good, she can get up to five litters. Bitches that have a tendency to get loose connective tissue around the teats should get fewer litters to avoid having a lot of stretched skin under the stomach. There may also be other factors that lead to the decision that a bitch will not be bred with more than a couple of times. The important thing is to consider the bitch’s health and well-being. The litters should not come too close. The bitch should not have more than one litter per year. (Besides that, the country’s laws must be followed.)

In order to avoid a rapidly increasing inbreeding rate, bitches and males should be used in breeding in equal measure (Selin 2017; Beuchat 2018). We must get away from the so-called “popular sire syndrome”, where a few popular males are used as studs with the result that all their offspring are half siblings. It is reasonable that a male gets up to five litters, just like the bitches. In the wild, dogs live in pairs, which means that the natural is that a male gets about as many litters as a bitch, which is highlighted in the following quote:

“The individual male cannot during his lifetime produce more offspring than a single female can feed. Cooperative breeding is nature’s ingeniously simple way of avoiding what we in the breeding of domestic animals use to call the ‘popular sire syndrome’.” (Sundgren 2004, my translation from Swedish)

The country’s legislation must be followed with regard to breeding debut and further, the breeder must consider the dog’s, especially the bitch’s, psychological maturity. To recommend is that the bitch does not go to breeding before the age of two and preferably that she waits until she is three to four years of age. The latter because fertility is at its highest and puppy mortality at its lowest at that age (Lindholm et al. 2015: 195), and because you have had more time to follow the bitch both regarding health and mentality.

Sources and further reading:

Beuchat, Carol. 2018. “Managing genetics for the future”. Course at the Institute of Canine Biology.

Calboli, Federico C. F. et al. 2008. “Population Structure and Inbreeding From Pedigree Analysis of Purebred Dogs”. Genetics 179, 593–601.

Lindholm, Åsa et al. 2015. Hunduppfödning i teori och praktik. Svenska kennelklubben.

Selin, David. 2017. ” HUNDuppfödarkursen”. Course at Hundutbildningsgruppen.

Statens jordbruksverk. 2019. ”Statens jordbruksverks föreskrifter och allmänna råd om hållande av hund och katt”. (SJVFS 2019:28). Statens jordbruksverks författningssamling.

Sundgren, Per-Erik. 2004. ”Naturens skydd av ärftlig variation”. Kennel Chanco.  


Background: The fertility reflects the viability and genetic diversity of the breed. Low fertility is a sign that the breed is not viable and that it has low genetic diversity, i.e. it is too inbred. Fertility broadly encompasses the whole cycle, from mating, gestation, to whelping and even to the puppy’s viability. In a more limited sense, “fertility” refers to successful mating, i.e. mating which leads to offspring. Few puppies are a sign of low fertility. According to Lindholm et al. both bitches and males are most fertile at three to four years old. They write that the bitch at this age gets the most number of puppies and that the puppy mortality is at its lowest (Lindholm et al. 2015: 195).

The Swedish Pug club under the Swedish kennel club, Mopsorden, addresses the issue of caesarean section in their breeding strategy, in the section “Reproduction and whelping”. In a health survey from 2011 it emerged that of the respondents’ dogs, 132 had become pregnant (during the same year?) and of these, 37 were subjected to caesarean section (”Rasspecifik avelsstrategi för mops”, 2015). This means that 28% of the bitches got a caesarean section when whelping. A corresponding number can be found in an article in which kennel club-affiliated dogs in the British kennel club were examined for caesarean section. The study was a questionnaire study and the material stretched from 1995 to 2002. 151 breeds were included in the study. The response rate was 24%. 142 Pugs were included in the study, and they had a total of 223 litters. Of these litters, 61 had been released by caesarean section. This is equivalent to 27.3% of caesarean sections (Evans and Adams 2010).

Note that the Pug is not counted among the breeds that have the highest frequency of caesarean sections. In that study, 92.3% of Boston terriers, 81.3% of French bulldogs, and 86.1% of English bulldogs were reported to have had caesarean sections. There are also some other breeds that are not brachycephalic which had a reporting of a high proportion of caesarean sections, such as e.g. Scottish Terrier with 59.8% and Dandie Dinmont Terrier, with 41.4% (Evans and Adams 2010, Table 1).

The cause of a caesarean section can be several, and the main in dogs is generally uterine inertia (Lindholm et al. 2015: 234). Another reason is that the puppy is too large, which is a common cause among brachycephalic dogs since they often have a large skull (see e.g. Lindholm et al. 2015: 234, 242). Evans and Adams refer to a Swedish study of 40 puppies of Boston terriers where a connection was found between large skull in the puppies and difficulty in whelping (Evans and Adams 2010: 113). In another Swedish study, the Pug was counted among the breeds that had difficulty in whelping and to those at risk for caesarean section. The researchers of this study also point out that the breeds that had a high risk of difficulties in whelping averaged 4.4 puppies in one litter, while those with low risk averaged 5.4 puppies. The Pug bitches averaged 3.1 puppies per litter (Bergström et al. 2006: 788f. and Table 3).

Goal: Each bitch should have a decent number of puppies per litter, which is 4–7 or some more. Caesarean sections should be unusual in the breed.

Photo: Nina Rimann
Mopszucht vom Odenwald

Strategy: Bitches who get a low number of puppies but give birth naturally should be followed up and combined with another male next time. If the low number remains at the second litter, consider taking her out of breeding. Bitches with uterine inertia at the first litter should be followed up. If the uterine inertia remains at the next litter, the bitch should not be bred with anymore. Bitches that need a caesarean section should not be bred with anymore if it is assumed to depend on the bitch’s constitution. If this does not seem to be the case, but a caesarean section is also required at the next delivery, the bitch shall, not be used in breeding again. In Sweden this is regulated by the Swedish National Board of Agriculture:

25 § A bitch or a female cat who has been released twice with a caesarean section is not allowed to be used in breeding anymore. (SJVFS 2019: 28, my translation from Swedish)

The cause of caesarean section in Pugs is often that the puppy is too large, because of too few puppies in the litter, and/or that the puppy’s head is too big. By producing a less brachycephalic Pug, the skull shape will be more optimal for whelping. This is done partly by choosing less brachycephalic Pugs for breeding and partly by carrying out breeding with a donor breed. Through crossbreeding, genetic diversity increases and thus fertility, which will lead to more puppies in each litter, and thus each puppy becomes smaller.

Genetic diversity is important not only in terms of female fertility. Through crossbreeding, we can improve the Pug’s anatomy and genetics and thus get a much healthier Pug population. Each breeder should consider this when choosing a partner for his/her dog. See further under “Genetic diversity”.

Sources and further reading:

Bergström, Annika et al. 2006. “Incidence and Breed Predilection for Dystocia and Risk Factors for Cesarean Section in a Swedish Population of Insured Dogs”. Veterinary Surgery 35, 786–791.

Evans, Katy M. and Vicki J. Adams. 2010. “Proportion of litters of purebred dogs born by caesarean section”. Journal of Small Animal Practice 51, 113–118.

Lindholm, Åsa et al. 2015. Hunduppfödning i teori och praktik. Svenska kennelklubben.

Mopsorden/SDHK. 2015 (1986). “Rasspecifik avelsstrategi för mops, Sverige”. Svenska kennelklubben. Accessed 160619.

Statens jordbruksverk (the Swedish National Board of Agriculture). 2019. “Statens jordbruksverks föreskrifter och allmänna råd om hållande av hund och katt”. (SJVFS 2019:28). Statens jordbruksverks författningssamling.

Chapters in Strategies for the breeding of Healthy Pugs