The breeding data used in the present study were not provided by a veterinary professional, yet their source is considered trustworthy as it is objective information obtained from an official body and which are not directly connected to a specific veterinary exam or dexterity. Furthermore, the obligation given by the KBS to provide both AoM and AoB  ensures that collected data include all litters born in a certain period of time. Litters of BMDs born in Switzerland without being tracked by AoM, AoB or DogBase entries are considered to be the product of non-FCI (Federation Cynologique Internationale) breeding, are not subject to the same rules as the litters included in the dataset and are, therefore, not (or only to a limited extent) comparable to the litters that were obtained following a certain generally accepted method . Such uniformity allowed to develop a large dataset of a single breed, with parameters which are easily comparable. Although these regulations provided an advantage, they need to be considered in the interpretation of the results and when comparing them to the literature, in particular regarding the age of the dam, the number of litters per bitch, and the IC of the litter. The KBS imposes a rule that bitches may only reproduce until 8 years of age  with only few exceptions whereas no age limit is imposed on sires. Males may sire six litters per year, while bitches may give birth to one litter per year . The inbreeding coefficient of the litter is calculated based on five generations and may not exceed 6.25% .
Mating data were collected exclusively using the AoM, which does not provide information on ovulation staging. No information was requested or provided about whether the bitch mated naturally or via artificial insemination, so no conclusions may be drawn in this regard. The use of artificial insemination is regulated by the FCI and is only permitted in bitches which have reproduced previously by natural mating  which means that the first litter of each bitch was evidently conceived without artificial insemination. The mating of the same male to the same female may be repeated once in cases of a satisfactory outcome (RoL) or up to 3 times in case of failure of the bitch to become pregnant (RoM). RoL and RoM were roughly equivalent, 49.5 and 51.5% of all breedings, respectively. Frequently, an agreement is made for a RoM without repeated payment to the owner of the sire. This would explain the high number of RoMs and the fact that more than 75% of all the RoMs were repeated only once. Failure to conceive in the bitch is frequently due to breeding management, abnormal cyclicity and also to pathologies or abnormalities within the reproductive tract. Although it is impossible to extrapolate what caused failure to conceive in 51.5% of mated bitches, a > 50% frequency of failure to conceive in these dogs is a reason for concern and it should be investigated. This is the first report of the frequency of RoL and RoM in a canine breed.
The interval between the first and the second mating was 1.5 ± 0.6 days in all bitches (regardless of whether or not becoming pregnant) and, as such, lower than the frequently advised interval of 48 h. This shorter interval compared to what should normally be done is probably a consequence of limitations in organization and availability of help, as most breeders included in the dataset do not breed dogs as their main sources of income and may, therefore, have difficulties staying close to the selected male for more than 2 days. Gestation length was calculated based on the interval between mating and parturition. The majority of bitches gave birth 63 ± 1 days after the first mating. This is in accordance with the gestational length reported after ovulation . Assuming that in the bitches of our study (a) ovulation staging was not done on a regular basis (which may justify the high rate of failure to conceive) and (b) general and reproductive health were normal, the high frequency of gestations of 63 ± 1 days indicates that (i) most breeders mated their bitches at the time of ovulation and (ii) an equally high percentage of bitches does not ovulate when expected. The possibility to obtain data on ovulation staging would be of great importance and further data collection is necessary considering that there might be a correlation between gestational length and the risk of C-section.
Litter size was 7.2 ± 3.1 pups and differed depending on parity and age of the dam, with younger bitches and primiparous bitches giving birth to larger litters than older and pluriparous dams. The mean litter size of this study was similar to [20,21,22] or higher than [23,24,25,26] what reported for BMD in the literature. Female fertility is higher at a younger age [5, 20, 23]. A possible influence of parity on litter size was previously reported [5, 23], although results differ between studies and/or breeds. Borge et al. , for example, found that primiparous bitches produced significantly larger litters. An increase in litter size between the first and second litter was observed in the Drever breed , followed by a continuous decrease from the third litter onwards. This pattern is similar to the BMD, characterized by an increasing litter size up to the third litter followed by a decrease in subsequent litters. In the present study litter size was compared only between primiparous and pluriparous bitches without considering parity. A direct comparison with the data described in the literature is therefore not possible. It has to be considered that the majority of the bitches within the present study were bred relatively early in life (mean age at birth: 3.9 ± 1.5 years), which suggests that prolificacy of bitches within the present dataset should be interpreted taking into consideration both age and parity of the dam.
The IC influences reproductive parameters such as litter size, stillbirth and neonatal mortality [20, 25]. Significantly larger litters are produced from bitches with IC of < 6.25% compared to bitches with ICs of 6.25–12.5% and over 12.5% . Although dams with inbreeding coefficients over 6.25% were present in this study, the maximum was 7.8% and the mean was 1.3%. As the KBS in general does not allow breeding of dogs with an IC higher than 6.25% no significant differences in IC at the dam, sire, or litter levels were observed in the present study. The only significant difference in the evaluation of inbreeding coefficients was observed when comparing bitches that had previous C-sections with bitches that did not. The relationship between IC and the risk of having a C-section is probably multifactorial therefore further investigations are needed on this respect. The overall sex distribution within litters (49.3% males versus 50.7% females) was similar to what has previously been reported in the literature [5, 27]. The incidence of stillbirth was 12%, which is higher than what has been previously reported for various breeds [20, 28, 29] and was significantly different between pluriparous and primiparous bitches of our study. A higher number of stillborn pups in primiparous bitches may be attributed to longer parturitions and less experience of the bitch, yet also the experience of the breeder which is assisting has to be taken into consideration. Further data collection is necessary to confirm such hypothesis.
The evaluation of the risk of C-sections within the dataset was the main aim of this study. Overall, incidences of 30.4% of C-sections and a mere 2% of elective C-sections were observed. When questioned about the low number of elective C-sections the KBS committee hypothesized that despite the perceived high risk of a C-section in this breed, most breeders try to avoid surgery thus letting the bitch proceed with a trial of labor and intervening only when a problem arises. The rate of C-sections within the dataset was higher than what was previously reported for the BMD  as well as for other breeds [29, 31]. In addition, more than half of all the bitches had at least one C-section in their reproductive career. Similar results have been observed the sires of our study, with some sires having an incidence of C-sections within their sired litters of up to 50%. Prior C-sections within a bitch’s reproductive history had a significant influence on the incidence of C-sections in subsequent parturitions - a finding that is in agreement with what has previously been described [12, 32]. Furthermore, our results indicate that bitches with a previous C-sections have smaller litters. Smaller litters and bitches of advanced age were found more frequently in the group of C-sections compared to the group of litters born via eutocic parturitions. Therefore, a possible additive effect of these factors in increasing the risk of C-sections cannot be excluded. A higher risk of C-section for litters of one or two pups has been reported , possibly due to an increased fetal size - which may result in a disproportion of the fetus [33, 34] or the birth canal - or due to insufficiency of fetal signaling for the induction of labor . The presence of a singleton or two pups should be a reason to advise the owner to request an elective C-Sect. . Interestingly, a statistically significant difference in stillbirths between C-sections and eutocic parturitions was not observed, yet the timing of C-sections is important as confirmed by the observation that significantly more pups were stillborn in C-sections performed at T1 than in C-sections at T0. Such results have been previously reported [7, 24, 29] and might be explained by prolonged fetal stress with prolonged stage 2 parturition. Litter size differed significantly as well, being significantly smaller with C-sections performed at T0 which confirms the observation that litters of one or two pups are at higher risk of dystocia than larger litters. Although the BMD is not generally considered a breed at risk for dystocia, further research is needed to determine whether differences in the phenotypical appearance following changes in the selection processes may have contributed to an increase in dystocia and consequent emergency C-sections within the studied population. Breeding of BMD in Switzerland is highly regulated as described above, yet no rules are imposed regarding the maximum number of C-sections a bitch may have prior to exclusion from breeding. Such a lack of regulation certainly rises an ethical concern, as does high incidence of emergency C-sections in bitches of breeds which are unlikely of or unable to whelp naturally. Regulations in this regard are not imposed by the FCI but may be imposed by the national breeding clubs. Limitations of the number of C-section a bitch may have would be useful, yet may not be considered as a solution. Investigation of the underlying conditions or reasons for an increased incidence of C-section or the inability to whelp naturally is of great importance in order to implement successful breeding strategies.