Uterine inertia is a significant cause of maternal dystocia in bitches. This study was undertaken to identify the factors influencing its incidence. Case records of canine dystocia presented to Veterinary College, Bengaluru during 2007 to 2012 were analysed. The overall incidence of dystocia in female dogs was 6.50 per cent among them maternal causes were 64.94 per cent of the cases in which primary uterine inertia accounted for nearly 99 per cent. Complete primary uterine inertia was encountered frequently in medium and large sized breeds, mainly Labrador Retrievers and German Shepherds. Highest incidence of complete primary uterine inertia was observed in female dogs aged less than 2 years and was about 8 per cent higher in dogs delivering for the first time. Female dogs carrying a single foetus or those with a litter size in excess of 8 foetuses appeared to be at high risk for complete primary uterine inertia.
The ultimate goal in the breeding programme of the bitch is obtaining healthy offspring while maintaining the health of the mother. As veterinary care has advanced, the demand for specialised veterinary services in dogs, including management of pregnancy and whelping has also increased. Consequently, there are considerable efforts being made to develop methods to optimize the outcome for each puppy and bitch.
For the neonate, labour represents the most critical phase contributing to the first minutes after birth and the act of parturition is the most anxious time for the dog breeder, as the puppy survival rate and the future reproductive status of the dam are influenced by the events at this stage.
Dystocia has conveniently been described as being maternal or foetal in origin and there is overwhelming evidence that in the bitch, maternal dystocia is encountered more frequently (Gaudet, 1985; Darvelid and Linde-Forsberg, 1994). There is also evidence that the most common cause of maternal dystocia is uterine inertia, representing 40 per cent (Gaudet, 1985) to 75.3 per cent (Darvelid and Linde-Forsberg, 1994) of all dystocia attributed to the dam. The most common form of uterine inertia in bitches is primary uterine inertia, which has been further classified as complete or partial (Van Den Weijden and Taverne, 1994). In complete primary uterine inertia, the bitch does not start labour. In partial primary uterine inertia, the bitch starts to deliver her puppies, but the labour ends prematurely, despite the presence of a patent birth canal (Bergstrom et al., 2006a). In view of the importance of primary uterine inertia as a highly significant cause of maternal dystocia, there is a need to identify the factors influencing its incidence. Similarly, there is very little or no information on the influence of such factors as the breed, size of the breed, age, parity and litter size on the incidence of primary uterine inertia in dogs, particularly from the Indian subcontinent. This study was carried out to analyse the incidence of foetal and maternal dystocia in bitch and the influence of the breed of the dam, age, size of the breed, parity and litter size on the occurrence of complete primary uterine inertia in the bitch.
Materials and Methods
Case records of canine dystocia presented to the obstetrical clinics in Department of Veterinary Gynaecology and Obstetrics, Veterinary College Hebbal, Bengaluru during the period of January 2007 to March 2012 were analysed to determine the incidence of foetal and maternal dystocia in dogs. The case sheets of bitches which had been diagnosed as cases of complete primary uterine inertia were further screened to evaluate the influence of various factors associated with complete primary uterine inertia. Following factors were considered for this retrospective study-
The data collected is analysed using frequency distribution and percentage to know the influence of different factors on complete primary uterine inertia in bitches.
Results and Discussion
Incidence of Dystocia
In the present study, the overall incidence of dystocia in female dogs was determined as 6.50 per cent (Table 1).
Table 1: Overall incidence of dystocia in canines
|No. of female dogs presented between January 2007 to March 2012||No. of Cases of Dystocia||Incidence (%)|
As per the earlier reports, the overall incidence of dystocia is less than 5 per cent (Root et al., 1995; Linde- Forsberg and Eneroth, 2000; Gill, 2002; and Sparkes et al., 2006) and 5.7 per cent (Bergstorm et al., 2009). The results of the present study are in close agreement with the above reports. However, a retrospective study by Darvelid and Linde-Forsberg (1994) of 182 cases of dystocia found that 42% of bitches that had whelped before had previously suffered from dystocia. The incidence of dystocia was almost 100 per cent in some breeds of dogs, especially those of achondroplastic type and those selected for large heads. Gill (2002) found that the frequency of dystocia varied from 9.1 per cent in Golden Retrievers to 85.7 per cent in Pekingese. Bergstorm et al. (2006b) using data from insurance claimed records of almost 2 lakhs insured bitches during the period between 1995 and 2002, estimated the overall incidence of dystocia to be around 16 per cent. In addition, there are some breeds which are achondroplastic and brachycephalic, where normal birth rarely if ever occurs, and elective caesarean operations are the routine (Arthur, 2001). Therefore, the reported variation in the frequency of dystocia in female dogs is because of the wide variation in the incidence of dystocia between different breeds, the tendency for the breeders to intervene, in some cases, prematurely and unnecessarily, the number of animals screened and the method of study used for arriving at the incidence.
Incidence of Maternal Dystocia
Dystocia is usually considered to be either of maternal or foetal in origin, and on the basis of this classification, in the present study, dystocia due to maternal origin was diagnosed much more frequently than of foetal origin. In 1355 cases of dystocia considered during retrospective analysis, dystocia due to maternal causes were diagnosed in 64.94 per cent of the cases (Table 2).
Table 2: Incidence of maternal and foetal dystocia in bitches
|Type of Dystocia||No. of Cases||Incidence (%)|
The incidence of maternal dystocia observed in the present study is in close agreement with the incidence (61.09 %) reported by Vibha (2012). Similarly, A higher incidence of maternal dystocia as compared to foetal causes has also been reported by Gaudet (1985); Darvelid and Linde- Forsberg (1994); Bennur (1999) and Narasimha Murthy (2011). The higher incidence of maternal dystocia observed in the bitch may be related to the prolonged duration of second stage of labour, temperament of the bitch and managemental practices such as nutrition and exercise.
Causes of Maternal Dystocia
In the present study, primary uterine inertia accounted for nearly 99 per cent of maternal dystocia (Table 3). Further, uterine inertia was classified as either complete or partial (Bergstrom et al., 2010) and partial primary uterine inertia was diagnosed more frequently than complete primary uterine inertia.
Table 3: Maternal causes of dystocia in bitches
|Types of Cause||No. of Cases||Incidence (%)|
|Primary complete uterine inertia||342||38.86|
|Primary partial uterine inertia||535||60.80|
Uterine inertia has been previously reported as the most common cause of maternal dystocia in bitches (Gaudet, 1985; Darvelid and Linde- Forsberg, 1994; Polster, 2006; Narasimha Murthy, 2011; Vibha, 2012). In the present study, vaginal septum and uterine torsion were also diagnosed as rare causes of maternal dystocia. Uterine torsion as a cause of maternal dystocia has been reported to be rare in canines (Brown, 1974; Bennett, 1980; Jones and Joshua, 1988; Arthur et al., 1989). Vaginal septum as a cause of maternal dystocia has also been reported by Freak (1962); Herr (1978) and Darvelid and Forsberg (1994). Other reported causes of primary complete uterine inertia include over-stretching of the myometrium due to hydro allantois or large litters, toxic degeneration of the uterus, senility, obesity and lack of exercise, uterine torsion and trauma (Bennett, 1974; Freak, 1975; Buckner, 1979; Arthur et al., 1989).
Factors Influencing Dystocia
The observation that uterine inertia was the most frequent cause of maternal dystocia in the bitch necessitated a need for further investigation into the various factors influencing the incidence of uterine inertia. The factors investigated were the breed, age, parity and litter size in animals with uterine inertia. However, the study was restricted to only the factors influencing the incidence of complete primary uterine inertia as this type of case of uterine inertia is much more difficult to handle than the primary partial uterine inertia.
Complete primary uterine inertia was encountered in seventeen different breeds of female dogs (Table 4).
Table 4: Breed wise incidence of complete primary uterine inertia
|S. No.||Breed||No. of Cases||Incidence (%)|
Dachshund, Labrodor Retrivers and German Shepherds accounted for a little over 40 per cent of all cases of complete primary uterine inertia. Freak, 1948 reported that Dachshunds are particularly prone for primary uterine inertia. A similar opinion was expressed by Narasimha Murthy (2011) and Vibha (2012). It is also stated that Scottish Terriers have a higher incidence of maternal dystocia and, in particular, primary uterine inertia which is believed to be of hereditary origin (Freak, 1962). In the present study, it was surprising to note that complete primary uterine inertia was encountered frequently in Labrador Retrievers and German Shepherds. These two breeds have not been reported to be particularly susceptible for maternal dystocia. It is probable that a higher frequency of uterine inertia recorded in these breeds may be due to a higher population of these breeds in and around Bangalore city, rather than due to breed disposition. Similarly, few cases of uterine inertia were recorded in some of the breeds and are perhaps due to the fact that their numbers are relatively few in Bangalore.
Size of the Breed
In the present study, complete primary uterine inertia was more frequently identified in medium and large sized breeds (Table 5).
Table 5: Incidence of complete primary uterine inertia based on the size of the breed
|Size||No. of Cases||Incidence (%)|
|Toy and small breed (Body weight < 10 kg)||62||18.13|
|Medium breed (Body weight 10-25 kg)||95||27.78|
|Large breed (Body weight 25-45 kg)||117||34.21|
|Giant breed (Body weight > 45 kg)||68||19.88|
These breeds accounted for nearly 62 per cent of all cases of complete primary uterine inertia. Narasimha Murthy, (2011); Vibha, (2012) have also reported that the incidence of primary uterine inertia was more frequently observed in medium and large sized breeds. In the present study, medium and large sized breeds were represented by 10 different breeds which also happen to be the preferred breeds among animal lovers in Bangalore city. Therefore the population of medium and large breeds such as Labrador Retrivers and German Shepherds are much higher in Bangalore city and therefore, the higher number of uterine inertia in medium and large breeds may be more because of their higher population. Studies of Darvelid and Forsberg (1994) also could not clearly establish a relationship between the body weight of the bitch and the incidence of dystocia.
Age of the Dam
In the present study, the highest incidence of complete primary uterine inertia was diagnosed in female dogs aged less than 2 years (30.12 %). Its incidence in animals of the age group of 2-4 years was 28.07 per cent (Table 6). Together, nearly 58 per cent of all complete primary uterine inertia was observed in animals less than 4 years of age. Similar observations have been made by Narasimha Murthy (2011) and Vibha (2012). Contrary to the above observation, Freak (1962), Smith (1974) and Freak (1975) reported that animals aged 5 years and above are more prone for dystocia, particularly due to uterine inertia. The low occurrence of inertia in animals aged 4 years and above, observed in the present study may be due to the fact that most canine owners prefer not to breed aged animals.
Table 6: Age wise incidence of complete primary uterine inertia in bitches
|Age (years)||No. of Cases||Incidence (%)|
|2 – 4||96||28.07|
|4 – 6||61||17.84|
|6 – 8||48||14.03|
The incidence of complete primary uterine inertia was about 8 per cent higher in female dogs delivering for the first time as compared to the incidence in pluriparous bitches. The incidence in complete primary uterine inertia was observed as 54.09 per cent and 45.91 per cent in primiparous and pluriparous bitches respectively (Table 7).
Table 7: Incidence of complete primary uterine inertia in bitches based on parity
|Parity||No. of Cases||Incidence (%)|
It was also observed that the incidence of complete primary uterine inertia decreased with increase in parity. A similar observation has been made by Vibha (2012). A higher incidence of complete primary uterine inertia in young female dogs is probably due to anxiety, fear, excessive interference of the owner, or change in certain managemental practices such as shifting the dog to unaccustomed area for the purpose of delivery.
In the present study, female dogs carrying a single foetus or those with a litter size in excess of 8 foetuses appeared to be at high risk for complete primary uterine inertia (Table 8).
Table 8: Incidence of complete primary uterine inertia in bitches based on litter size
|Litter Size||No. of Cases||Incidence (%)|
Freak (1962) reported that the commonest single cause observed in animals with primary complete uterine inertia was low fecundity. The author suggested that low fecundity and its accompanying low hormonal influence appeared to result in simple and complete failure to initiate whelping. He also recorded a higher incidence of uterine inertia in animals with high fecundity and attributed the cause of uterine inertia in such animals to be due to uterine distension. Arthur et al. (1989) agreed that overstretching of the myometrium by an excessively large litter size was an important cause of uterine inertia in dogs.
Dystocia due to maternal causes was encountered more frequently than foetal causes accounting for about 64.94 per cent. Further, among the maternal causes, complete primary and partial primary uterine inertias account for nearly 99 per cent. Dachshund, Labrador Retrievers and German Shepherds were the most frequent breeds in which dystocia were diagnosed to be due to complete primary uterine inertia. It was further observed that primary uterine inertia was much more common in animals under the age of 4 years. The size of the breed appeared to have a significant effect on the occurrence of primary uterine inertia, with medium and large sized breeds being more commonly diagnosed as cases of primary uterine inertia. Primary uterine inertia was slightly more common in primiparous animals and was observed to be more frequent in animals carrying a single foetus or an excessively large litter.