Date Published: March 21, 2007
Publisher: BioMed Central
Author(s): Catharina Linde Forsberg, Gunilla Persson.
Dystocia occurs more commonly in some breeds of dogs than others. The Boxer breed is one of the highrisk breeds for whelping problems. The aim of this study was to document some reproductive parameters and the frequency of dystocia in Boxers.
Two questionnaires were sent to the breeders of Boxers in Sweden during 1994 to 1997. Data from 253 whelpings and 1671 pups was received, which constitutes 56.5% of all Boxer litters registered with the Swedish Kennel Club during these years. Data was analysed using Chi-square test, and Fischer’s exact test.
Dystocia occurred in 32% of the individual bitches, and in 27.7% of all the whelpings. Caesarian section was performed in 22.8% of all the whelpings and in 80.1% of the cases of dystocia. Medical treatment was tried in 20 cases but was successful only in 5 (25%). The dystocia was of maternal origin in 68.6% and of fetal origin in 28.6% of cases. The most common reasons for dystocia were primary uterine inertia (60%) and malpresentation of the fetus (26%). Dystocia increased with increasing age of the bitch from four years of age. Average litter size was 6.6 (± 2.2) pups born, and 5.0 (± 2.1) pups registered. Pup mortality was 24%. Stillbirths accounted for 6.1% of the pup deaths and 1% died in the neonatal period, while 15.6% of the pups were euthanised, the majority because they had disqualifying white coat colour. Cryptorchidism was observed in 9.8% of the male pups born and in 13.4% of the male pups that were registered.
The Boxer suffers a high frequency of dystocia, mainly due to uterine inertia, but also fetal malpresentation. Breeders should be adviced to include easy whelpings in their breeding program.
Dystocia is defined as difficult birth or the inability to expel the fetus through the birth canal without assistance. Traditionally, dystocia is classified as being of either maternal or fetal origin, or a combination of both. In a study of 182 bitches of many different breeds that were brought to a veterinary hospital because of dystocia, Darvelid & Linde-Forsberg (1994) found that 75.3% of the cases of dystocia had a maternal cause while 24.7% were of fetal origin. Previously Gaudet (1985) , in a similar survey reported that 60% of dystocias were due to maternal causes while 40% had foetal causes. The overall incidence of dystocia in the bitch is probably below 5 per cent, but it may amount to almost 100 per cent in some breeds of dogs, especially those of the achondroplastic type and those selected for large heads [1,3-7]. Gill (2002) , studying 15 breeds of dogs found dystocia to vary in frequency from 9.1% in Golden Retrievers to 85.7% in Pekingese, and Caesarian sections from 5.9% in Rough Collies to 60% in Pekingese. Eneroth et al. (2000)  reported that the frequency of Caesarian sections in Boston Terriers was 62%, and in French Bulldogs 43%. Recently, Bergström et al. (2006) , using data from insurance claim records from almost 200,000 insured bitches in the period 1995–2002, estimated the overall incidence of dystocia to be around 16%, and Caesarian section was performed in 63.8% of cases.
Out of a total of 448 Boxer litters registered by the Kennel Club during the years of the study, 253 (56.5%) are included in the surveys.
This study is based on information from breeders answering the questions in the two questionnaires from the Boxer Club. Some additional information was obtained by personal phone calls. The questionnaires were sent out at varying times after the birth of the litters and the answers, therefore, are dependent on the record keeping practices of the breeders. Although most breeders make notes of their breeding activities, some were not able to answer all the questions, and some had misunderstood some of them. In this kind of studies there is also a risk that the outcome of the whelping, in one way or the other, may influence the motivation for the breeder to answer the questions, which may have biased some of the data. The answering frequency of 56.5% is rather high for this kind of studies, but still not high enough to exclude that some of the conclusions drawn may be not entirely representative for the breed. However, the Boxer Club and the breeders participating in this study were highly motivated and the information is, therefore, likely to adequately reflect the degree of the whelping problems in this breed.
In this study the frequency of dystocia in the Boxer breed was found to be considerably higher than expected in the average dog population. Primary uterine inertia was the most common problem, and increased from four years of age. Some bitches experienced primary uterine inertia during more than one whelping. This is a condition that is considered to have a hereditary component and therefore the bloodlines in which this problem is common should be identified, and breeders should be adviced to avoid breeding from, or combining, such lines. It should, however, be differentiated between bitches that suffer from true primary uterine inertia and those that experience uterine inertia due to carrying only one or two pups, or a very large litter. Also, bitches that have suffered from secondary inertia due to exhaustion from an oversized or malpositioned fetus need not necessarily have a hereditary predisposition for inertia. However, should dystocia due to malpositioned fetuses become overrepresented in some lines the possibility that this is due to some hereditary factor in those lines need to be considered.
The author(s) declare that they have no competing interests.
The planning of the study was done by CLF, the compilation of data by GP, and the analyses of results and the writing of the manuscript was done in cooperation.