Genetic Welfare Problems of Companion Animals

An information resource for prospective pet owners

BostonTerrier

Boston Terrier

Dystocia due to Foetal-pelvic Disproportion

Related terms: foetal-maternal disproportion, dorso-ventrally flattened pelvic canal

Outline: Because of changes in body shape (of both puppy and mother) due to selection for particular features, there is commonly a serious mismatch between the size of Boston terrier pups and the birth canal of their mothers, such that birth is not possible except by caesarian and, unless this is done, the birth will end in the painful death of the mother.  


Summary of Information

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1. Brief description

Dystocia is the veterinary term used to describe any difficulties in giving birth. Dystocia can lead to suffering during attempts at giving birth and frequently requires veterinary intervention. 92% of Boston terrier pregnancies end in delivery through caesarean section. Many of these caesareans are due to dystocia but some are probably performed electively to prevent dystocia or breathing problems for the bitch during parturition. Birth problems are common in Boston terriers due to a combination of bitches often having an abnormally-shaped pelvis and the puppies having relatively large heads due to brachycephaly (abnormal head shape).

2. Intensity of welfare impact

Dystocia causes severe pain and distress. This distress is intensified in Boston terriers, (a brachycephalic breed), because they often have pre-existing general problems with their breathing that can lead to difficulty in coping with stress and physical exertion. Without intervention dystocia will lead to the death of the puppies and often of the mother.

3. Duration of welfare impact

Dystocia can lead to attempts to give birth (parturition) lasting for hours and possibly days if veterinary intervention is not sought.

4. Number of animals affected

The majority of pregnant female Boston terriers would suffer dystocia if allowed to give birth naturally and elective caesareans were not carried out. Currently 92% of Boston terrier births are by caesarean in the UK (Evans and Adams 2010).

5. Diagnosis

A diagnosis of dystocia is made if a mother fails to produce live young within defined time periods after the onset of parturition. Radiographs can be used to confirm foetal-pelvic disproportion.

6. Genetics

No specific genes have currently been identified but the problem of foetal oversize is connected with brachycephalic breed characteristics such as having a relatively short nose and large head. An abnormally flattened pelvic canal has also been identified in Boston terriers, which contributes to difficulties in giving birth but the genetics of this have not been identified.

7. How do you know if an animal is a carrier or likely to become affected?

It is the norm for Boston terriers to have this problem. Thus finding a puppy that has been delivered naturally is difficult. Radiographs of the pelvis of a mature bitch can give some indication of the pelvis being abnormally shaped. Producing Boston terrier puppies without the large heads that contributes to dystocia is not possible as the brachycephalic head shape is a breed characteristic.

8. Methods and prospects for elimination of the problem

With 92% of births being via caesareans, this breed is unable to be perpetuated without surgical intervention.

Trying to alter conformation, to allow natural births, whilst keeping a reasonably large gene pool for the breed is likely to require out-breeding.

 

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1. Clinical and pathological effects

Dystocia (difficulty in giving birth) has multiple causes but they are generally divided into factors affecting the mother and factors affecting the foetus (Jones & Joshua 1988) and both sorts affect the . Boston terrier and lead to a very high rate of dystocia in this breed (Eneroth et al 1999). A recent report indicated that 92% of Boston terrier litters are delivered by caesarean section rather than naturally via the birth canal  (Evans & Adams 2010).

The major contributing maternal factor is that the shape of the pelvis is often abnormal. The front of the pelvis, into which the puppy must enter during the birth process, should be pear shaped, with the vertical axis longer than the horizontal axis (Jones & Joshua 1988). In Boston terriers this is typically reversed, with the pelvic inlet being oval, and often having a vertical dimension shorter than the horizontal dimension (Eneroth et al 1999).

The major contributing foetal factor is that Boston terrier puppies have relatively large heads in relation to their bodies. Larger head dimensions are also related to the total weight of the puppy, so, in Boston Terrier puppies, the greater the puppy weight, the greater the risk of dystocia (Eneroth et al 1999).

It is not known what proportion of  the large number of caesareans carried out on Boston terriers are elective procedures undertaken to prevent any chance of dystocia and consequent complications for the bitch or puppies, and what proportion are carried out once dystocia has occurred.

Boston terriers are included among the brachycephalic breeds – characterised as having relatively short faces and having a high prevalence of difficulty breathing (Evans & Christensen 1979,Brown & Gregory 2005, Bannasch et al 2010). Dogs with so-called brachycephalic airway disease have a combination of a shortened and distorted upper airway, narrow nostrils, an elongated soft palate, and an abnormal larynx (voice box). Secondary to these airway obstructions, dogs can develop collapsed airways, especially involving the larynx and trachea. These defects commonly make it difficult for brachycephalic dogs to breathe adequately whilst undertaking normal activity and stress caused by exercise, excitement, heat or giving birth can lead to airway collapse and death. So, part of the reasons for this high caesarean rate may be that breeders routinely arrange for caesarean sections so as to avoid the asphyxiation of a whelping bitch that might otherwise occur during a normal birthing process (Harvey 1989).

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2. Intensity of welfare impact

Dystocia is a severe welfare problem for the affected bitch which, if untreated, will usually lead to her death. Even with treatment it results in a higher rate of death in the puppies, unless treatment is prompt (Jones & Joshua 1988). Treatment of a bitch that is having difficulty giving birth involves travel and examinations at a veterinary practice – both stresses that cause further suffering to a brachycephalic dog with breathing difficulties. Uterine contractions are painful and control of this pain is difficult in the home environment, so a longer birthing process causes more prolonged and severe pain than usual. Caesarean section is usually required to treat a Boston terrier with dystocia. Unplanned, emergency caesarean sections are likely to have a higher welfare impact than either natural birth or elective caesarean, and a higher death rate for the puppies. Caesarean sections are major surgical procedures for any bitch to undergo and anaesthesia has a significantly higher risk of death in brachycephalic breeds due to their abnormal respiratory tracts and respiratory compromise.

It is likely that a significant reason for the high incidence of caesarean section in the Boston terrier is that elective caesareans are being performed. It can be argued that this reduces the welfare implications associated with foetal-pelvic disproportion for these dogs (Evans & Adams 2010). There is also an ethical dimension for veterinary surgeons carrying out an elective surgical procedure in an animal, that at the time of the procedure been performed, did not have a condition definitely requiring it.

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3. Duration of welfare impact

The welfare impact of dystocia lasts only for the period when the dog is having difficulty giving birth and the following days when she is recovering. Untreated, dystocia can be endured for up to 24-36 hours although, as this time goes on, progressive death of the puppies will occur; after 36 hours of dystocia the survival of the bitch is certainly compromised (Jones & Joshua 1988). If a caesarean is performed the female will be pain from the surgery for some days although effective analgesia should be available. A further issue is that if live puppies have been delivered then they should be sucking milk. This will be happening around the surgical wounds which will cause extra pain to the bitch in the first week, or so, after the procedure.

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4. Number of animals affected

92% of Boston terrier litters are reported to be delivered by caesarean section rather than naturally (Evans & Adams 2010). Boston terriers are one of three breeds excluded from insurance claims for dystocia in certain parts of the world (Bergström et al 2006). This is because dystocia is so common in the breed that it is uneconomic for insurance companies to include this cover. The other excluded breeds are the English and French bulldogs which are reported to have caesarean rates of 86 and 81% respectively (Evans & Adams 2010).

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5. Diagnosis

A normal labour is divided into three parts. In first-stage labour, the body prepares itself for birth with the cervix relaxing and dilating. During this stage, if left alone, the bitch in the wild would seek seclusion and dig a den. The second stage involves the loss of uterine fluids, progressively more vigorous straining and birth of the puppies. The third stage of labour is delivery of the foetal membranes and, in dogs, this stage is mixed with the second stage, as membranes are sometimes expelled with their puppy and sometimes afterwards. In some cases of dystocia, stage two never starts and dystocia is diagnosed once a dog is recognised not to have progressed from stage one to stage two after about 24 hours. Otherwise, dystocia may be diagnosed when stage-two labour has been happening for about two hours without a puppy having been delivered (Jones & Joshua 1988). Radiographs can be used to confirm foetal-pelvic disproportion and if this is present it can be predicted that normal birth will be impossible.

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6. Genetics

The genetic causes of foetal-pelvic disproportion in Boston terriers are complicated as they are directly connected with the breed standard of the dogs, which requires them to be brachycephalic with a deep chest. The exact cause of the pelvic canal flattening is unknown. The area of the canine genome responsible for brachycephalia has been identified and two genes implicated (Bannasch et al 2010). There are no genetic tests to help determine which dogs should be bred from.

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7. How do you know if an animal is a carrier or likely to become affected?

All female Boston terriers are at risk of this condition. All puppies have the brachycephalic head shape and many bitches are unable to give birth naturally because of this and their pelvic abnormalities. Thus it is very difficult to find a puppy which has not been born via caesarean section. Ideally any puppy purchased would have had a natural birth without the bitch suffering any dystocia. No guidance based on scientific evidence can currently be given on how to choose a female Boston terrier puppy that will be less likely to have dystocia if bred from. Mature bitches could be radiographed prior to mating and bitches with abnormal pelvic anatomy not used in breeding programmes. A key here is that the vertical dimension of the pelvic inlet should be larger than the horizontal dimension (Jones & Joshua 1988). However this process has not yet been scientifically proven as a method for selecting bitches in which dystocia will be less likely and all bitches will still have a vulnerability to dystocia due to the brachycephalic head shape of the pups.

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8. Methods and prospects for elimination of the problem

It might be argued that breeding from dogs that had been born naturally would help to select for a strain (population) able to give birth naturally in the future. However, allowing all births to progress naturally, to test whether or not pups could be delivered naturally  might create more suffering in the short term and might lead to the deaths of puppies and bitches so this seems an unsuitable way forward.

It may be possible to assess the size and shape of the pelvises of prospective mothers; as has been described by Eneroth et al (1999). They found that bitches with a vertical pelvic dimension larger than their horizontal dimension were less likely to have suffered from dystocia. Breeding from such dogs may be reasonable and helpful in lowering the incidence of dystocia. However, the details of such a scheme have not yet been proposed and the proposal has certainly not been validated. This radiographic assessment would require general anaesthetic and this, while not involving pain, does include a stressful day for the dog for no individual benefit and would be a minor welfare issue in itself.

Given the high proportion of animals that appear to suffer from foetal-pelvic disproportion in this breed the number of normal animals may be too low to use in a selective breeding programme within the breed. An issue with concentrating the gene pool in this manner is that inbreeding is likely, exacerbating other genetic defects.

Reducing the relative head size of puppies through selection is theoretically possible and, if so, would probably help in reducing the incidence of dystocia. This might require a substantial change in the breed confirmation and unpredictable changes in conformation could also occur as head size was reduced. For example, it is possible that worsening of brachycephalic airway disease or narrowing of the pelvic canal could occur over generations; with no net overall benefit to the incidence of dystocia.

Reducing the extent and severity of brachycephalic airway disease in the breed would probably have an impact.

Since it is likely to be very hard, if not impossible, to ensure that that timely veterinary intervention will always be available to manage dystocias wherever and whenever these dogs may breed, and because of the stressors that can occur even with veterinary intervention, animal welfare will be best served by not breeding from animals that are unlikely to be able to give birth naturally.

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9. Acknowledgements

UFAW is grateful to Rosie Godfrey BVetMed MRCVS and David Godfrey BVetMed MRCVS for their work in compiling this section

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10. References

Bergström A, Nødtvedt A, Lagerstedt A and Egenvall A (2006) Incidence and breed predilection for dystocia and risk factors for cesarean section in a Swedish population of insured dogs. Veterinary Surgery 35(8): 786-791

Bannasch D, Young A, Myers J, Truvé K, Dickinson P et al (2010) Localization of Canine Brachycephaly Using an Across Breed Mapping Approach. PLoS ONE 5(3): e9632. doi:10.1371/journal.pone.0009632

Brown D and Gregory S (2005) Brachycephalic Airway Disease. In: BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery. Eds, D. Brockman & D. Holt. BSAVA, Cheltenham. pp 84

Eneroth A, Linde-Forsberg C, Uhlhorn M and Hall M (1999) Radiographic pelvimetry for assessment of dystocia in bitches: a clinical study in two terrier breeds. Journal of Small Animal Practice 40: 257-264

Evans K and Adams V (2010) Proportion of litters of purebred dogs born by caesarean section. Journal of Small Animal Practice 51: 113–118

Evans HE and Christensen GC (1979) Miller’s Anatomy of the dog. W.B. Saunders, Philadelphia, USA. pp 118–121

Harvey CE (1989) Inherited and congenital airway conditions. Journal of Small Animal Practice 30: 184-187

Jones D and Joshua J (1988) Some problems of parturition. In: Reproductive Clinical Problems in the Dog, 2nd Ed. Wright, London. pp 87-112

© UFAW 2011


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