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Genetic Welfare Problems of Companion Animals
An information resource for prospective pet owners
Yorkshire Terrier
Tracheal Collapse
VeNom term: Tracheal collapse (VeNom code: 2003).
Related conditions: respiratory infection, pulmonary oedema, cardiomegaly; allergic respiratory disease; obesity
Outline: Tracheal collapse is a chronic progressive disease affecting the rings of cartilage in the trachea and which keep open this airway to the lungs. The condition is thought to be congenital, ie present from birth and is a result of changes to the cartilage that cause it to soften and weaken. Dogs with the condition have a dry, harsh or “honking” cough and noisy, laboured breathing. Factors that exacerbate these signs include obesity, respiratory infections, fluid build-up in the lungs (pulmonary oedema), abnormal enlargement of the heart (cardiomegaly) and allergic respiratory disease. Dogs with the condition exhibit breathing difficulties at rest, which can worsen when dogs are distressed, excited, exercising or when the weather is hot and humid.
Tracheal collapse is seen most commonly in middle aged to older dogs and in toy and miniature breeds, especially the Yorkshire terrier. Management of the clinical signs of tracheal collapse is not always effective, and the condition may be fatal, in severe cases.
As tracheal collapse is more common in Yorkshire terriers, than in other breeds, it is suspected to be an inherited trait in this breed. However, with the limited state of knowledge on the causal factors of tracheal collapse, the best advice that can be offered to prospective breeders is to avoid breeding between affected dogs or from dogs with severely affected relatives (ie grade 2-4), including grandparents, siblings, previous offspring and siblings of parents.
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Summary of Information
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1. Brief description
The trachea, or ‘windpipe’, is a thin-walled tube of tissue through which air is transported to and from the lungs. Rings of cartilage along the trachea give it structure and hold the airway open. Tracheal collapse is a result of cellular changes to the cartilage of these tracheal rings that affects the rings’ structural integrity causing them to soften and weaken. The trachea branches at its base into two smaller airways, the left and right bronchus, which enter the lungs, and bronchial collapse (bronchomalacia) also commonly occurs in dogs with tracheal collapse (Johnson & Pollard 2010).
Collapse of the trachea causes obstruction, inflammation, and increased mucus secretion and congestion in the airway. The most common clinical sign of tracheal collapse is a dry, harsh or “honking” cough and noisy, laboured breathing. Affected dogs may also have a bluish discolouration of the skin, due to poor circulation of oxygenated blood around the body. Once clinical signs develop, the condition is progressive, since persistent coughing can promote changes in the tracheal wall lining and results in an over-production of mucus, which, in turn, further exacerbates coughing.
Tracheal collapse occurs almost exclusively in small breeds of dog, and it is suggested that it is caused by a congenital abnormality ie present from birth (Done et al 1970). Factors that contribute to an exacerbation of symptoms include obesity, respiratory infection, fluid build-up in the lungs (pulmonary oedema), abnormal enlargement of the heart (cardiomegaly) and allergic respiratory disease. Tracheal collapse may also cause liver damage, possibly due to reduced delivery of oxygen to the liver.
2. Intensity of welfare impact
Affected dogs suffer difficulties breathing and this is likely to cause bouts of respiratory distress, and to inhibit their ability to exercise normally or play. Breathing difficulties are seen in affected dogs at rest, and these can worsen when dogs are distressed, excited, exercised or when the weather is hot and humid weather. The complications and associated diseases of tracheal collapse may cause other problems, such as weakness and fatigue. Affected dogs that are overweight or obese may suffer more intense symptoms.
There is no cure for the disease, but it can be managed by avoiding exercise in hot weather, weight-loss, and by avoiding the use of collars or harnesses that put pressure on the windpipe. Medication to supress coughs, clear mucus and reduce inflammation may also alleviate the symptoms of tracheal collapse. Surgical treatment of tracheal collapse should only be considered for dogs whose symptoms cannot be managed by such actions or through medication.
3. Duration of welfare impact
Tracheal collapse commonly affects middle aged to older toy breed dogs. The respiratory distress that affected dogs suffer from can be prolonged, and occur for weeks or years before the clinical signs become severe enough for the owner to make the decision to take the dog to the veterinary surgeon.
Management of the symptoms of tracheal collapse is not always effective, and the condition may be fatal, sometimes rapidly after diagnosis, in severe cases.
4. Number of animals affected
Yorkshire terriers are over-represented in dogs that suffer from tracheal collapse; making up approximately 65% of cases.
There is no reported difference in the distribution of males and females affected with tracheal collapse.
5. Diagnosis
Veterinary surgeons diagnose tracheal collapse using one or more diagnostic tests - radiography, fluoroscopy, tracheoscopy and ultrasonography. Signs looked for are a response to tracheal palpation and dynamic collapse on respiration with inflammation and thickening of the dorsal tracheal membrane.
6. Genetics
There has been no research to date on the mode of inheritance or genetic mechanisms underlying tracheal collapse. Tracheal collapse affects more Yorkshire terriers than would be expected, and therefore is suspected to be an inherited trait.
7. How do you know if an animal is a carrier or likely to become affected?
It is not possible to be sure whether an individual is a carrier or likely to be affected as the exact mode of inheritance of tracheal collapse is unknown, however Yorkshire terriers are more likely to suffer tracheal collapse than other breeds.
8. Methods and prospects for elimination of the problem
With the limited state of knowledge on the causal factors of tracheal collapse, the best advice that can be offered to prospective breeders is to avoid breeding between affected dogs or from dogs with severely affected relatives (ie grade 2-4), including grandparents, siblings, previous offspring and siblings of parents.
For further details about this condition, please click on the following:
(these link to items down this page)
- Clinical and pathological effects
- Intensity of welfare impact
- Duration of welfare impact
- Number of animals affected
- Diagnosis
- Genetics
- How do you know if an animal is a carrier or likely to become affected?
- Methods and prospects for elimination of the problem
- Acknowledgements
- References
1. Clinical and pathological effects
The trachea, or ‘windpipe’, is a thin-walled tube of tissue through which air is transported to and from the lungs. Rings of cartilage along the trachea give it structure and hold the airway open. Tracheal collapse is a result of cellular changes to the cartilage of these tracheal rings that affects their structural integrity and causes them to soften and weaken.
Cartilage is an important structural tissue of the body; it is firm, but softer and more flexible than bone and in adult animals it gives support and structure to parts of the body that lack bone, such as the external ears and the airways of the lung. Cartilage is characterized into three types, based upon its degree of flexibility, and consists of specialized cells called chondrocytes surrounded by a dense extracelluar matrix of collagen and elastin fibres that are all embedded in a rubbery ‘ground substances’ that fills the spaces between the fibres and the cells. The molecules that form the ground substance, called glycosaminoglycans, are very good at absorbing water such that 90% of the normal extracellular matrix is comprised of water. This water plays an important role in ability of cartilage to resist compression.
In affected animals there are changes to the extracellular matrix and a reduction in normal levels of calcium, and the complex carbohydrate molecules (glycosaminoglycans and chondroitin sulfate; Dallman et al 1988), which are involved in the maintenance and support of collagen and elastin. These changes reduce the ability of the cartilage of the tracheal rings to absorb and retain water, leading to weakening and decreased rigidity of the trachea rings so that the rings appear flattened. As the trachea reaches the lungs it branches into two smaller airways, the left and right bronchus, and bronchial collapse (bronchomalacia) can also commonly occur in dogs with tracheal collapse (Johnson & Pollard 2010). Collapse can affect the cervical or intrathoracic trachea, or bronchial walls, or it may affect multiple regions. Tracheal collapse can be graded from 1 to 4 in severity, with each grade representing a 25% reduction in the diameter of the airway (ie grade 1 is 25% reduction, grade 2 is 50%; Tangner & Hobson 1982).
Collapse of the trachea causes airway obstruction, inflammation, swelling (oedema), increased mucus secretion and mucus trapping in the airways (Maggiore 2014). The most common clinical sign for which the dog is presented to the veterinarian is a dry, harsh or “honking” cough. Other clinical signs include respiratory distress (ie difficulty breathing), noisy breathing and a persistent cough. Dogs may also present with bluish discolouration of the skin, due to poor circulation of oxygenated blood around the body. Once clinical signs develop, the condition is progressive, since the coughing can lead to persistent inflammation of mucosal cells lining the tracheal walls, which leads to permanent changes in the wall lining and affects the normal function of the ciliary cells that clear the trachea from mucus and debris. The result is an over-production of mucus, which in turn exacerbates coughing. Affected dogs are at risk of respiratory infections, since the normal mechanisms to remove debris and microbes are impaired.
Tracheal collapse occurs almost exclusively in small breeds of dog, and it is suggested that it is caused by a congenital abnormality ie present from birth (Done et al 1970). There are other factors that may cause or exacerbate symptoms of tracheal collapse. Affected dogs that are over-weight or obese may suffer increased intensity of symptoms, since there is extra pressure on the airways. Respiratory infections, fluid build-up in the lungs (pulmonary oedema), abnormal enlargement of the heart (cardiomegaly) and allergic respiratory disease can also exacerbate or cause the symptoms of tracheal collapse (White & Williams 1994). Tracheal collapse may also cause damage to the liver, possibly due to the low levels of oxygen reaching the liver (Bauer et al 2006).
2. Intensity of welfare impact
Tracheal collapse is a chronic progressive disease. Affected dogs suffer difficulties breathing and this is likely to cause distress, and inhibit their ability to exercise normally or play. Breathing difficulties are seen in affected dogs at rest, and these can worsen if the dog is in states of emotional distress or excitement, as well as during exercise. Symptoms may also worsen in hot and humid weather conditions. Severe respiratory distress with pale or blue gums or collapse is treated as a medical emergency situation.
The complications and associated diseases of tracheal collapse may not be painful, but are likely to cause further malaise, eg weakness and fatigue due to impaired respiratory, cardiovascular or liver function.
There is no cure for the disease, but it can be managed by avoiding exercise in hot weather, weight-loss, or avoiding the use of collars or harnesses, which put pressure on the windpipe. Medication to supress coughs, clear mucus and reduce inflammation may also alleviate the symptoms of tracheal collapse. Surgical treatment of tracheal collapse should only be considered for dogs whose symptoms cannot be managed by such actions or through medication, since the risks of death and complications are reported to be high (White & Williams 1994), and often there is not complete resolution of symptoms (Tangner & Hobson 1982).
3. Duration of welfare impact
Tracheal collapse commonly affects middle to older age toy breeds of dogs. In most studies of tracheal collapse, the average age of diagnosis was 6.5 years, but it could range from 1 to 15 years old (White & Williams 1994, Buback et al 1996).
The respiratory distress that affected dogs suffer can be considerably prolonged. Even before the symptoms are severe enough to be taken to the veterinarian, there may periods of respiratory distress, ranging from weeks to years. Some owners of dogs diagnosed with tracheal collapse reported respiratory distress for as long as 7 years and even “all its life” (Done et al 1970).
In one study of 100 dogs with tracheal collapse, 7 dogs died within the first four weeks of presentation, and 22 dogs had signs that remained uncontrolled after 1 month of medical and/or conservative management (White & Williams 1994). Buback et al (1996) reported that younger dogs (less than 6 years old) had more severe tracheal collapse but did better after surgery than old dogs (older than 6 years); the older dogs suffered more postoperative complicated and a poorer long term outcome.
4. Number of animals affected
Tracheal collapse is commonly reported in miniature or toy breeds. In particular, Yorkshire terriers are over-represented in dogs with tracheal collapse. In studies of dogs with tracheal collapse, Yorkshire terriers made up approximately 65% of cases (White & Williams 1994, Buback et al 1996, KiChang et al 2004).
There are no reported differences in the distribution of males and females affected with tracheal collapse.
5. Diagnosis
Tracheal collapse is diagnosed with one or more diagnostic tests - radiography, fluoroscopy, tracheoscopy and ultrasonography. Veterinarians diagnose tracheal collapse on the basis of a persistent cough on expiration, response to tracheal palpation and endoscopic confirmation of the anatomic tendency to collapse, with inflammation and thickening of the dorsal tracheal membrane. The degree to which the trachea has collapsed is graded on a scale from 1 to 4, with 4 being the most severe).
6. Genetics
Tracheal collapse is presumed a congenital defect, and it most commonly occurs in small breeds of dog, of which the Yorkshire terrier is over-represented. This, therefore, suggests an inherited basis. However, there has been no research to date on the mode of inheritance or genetic mechanisms underlying tracheal collapse.
7. How do you know if an animal is a carrier or likely to become affected?
Dogs of miniature and toy breeds are predisposed to tracheal collapse, especially Yorkshire terriers. However, the exact mode of inheritance of tracheal collapse is unknown so it is currently not possible to test whether a dog is a carrier or likely to be affected.
8. Methods and prospects for elimination of the problem
Since the genetic mechanisms of tracheal collapse are unknown, the advice that can be given to eliminate the problem is limited (Meyers-Wallen 2003). If, as suspected, tracheal collapse is an inherited defect, then prevention of the condition is limited to controlling the genetic predisposition of the disorder in the Yorkshire terrier and other affected breeds. However, the problem is more complex since dogs may not show clinical signs until they are exposed to one or more other contributory factors (eg respiratory infection, allergic reaction), and further, dogs may recover from symptoms if the environment is carefully managed (e.g. kept smoke-free, avoid neck collars). With the current state of knowledge on the causal factors of tracheal collapse, the best advice that can be offered to prospective breeders is to avoid breeding between affected dogs or from dogs with severely affected relatives (ie grade 2-4), including grandparents, siblings, previous offspring and siblings of parents.
9. Acknowledgements
UFAW thanks Dr Emma Buckland (BSc, PhD), Dr David Brodbelt (MA VetMB PhD DVA DipECVAA MRCVS) and Dr Dan O’Neill (MVB BSc MSc PhD MRCVS) for their work in compiling this section.
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10. References
Bauer NB, Schneider MA, Neiger R and Moritz A (2006) Liver Disease in Dogs with Tracheal Collapse. Journal of Veterinary Internal Medicine 20: 845
Buback JL, Boothe HW and Hobson HP (1996) Surgical treatment of tracheal collapse in dogs: 90 cases (1983-1993). Journal of the American Veterinary Medical Association 208: 380–4
Dallman MJ, McClure RC and Brown EM (1988) Histochemical study of normal and collapsed tracheas in dogs. American Journal Of Veterinary Research 49: 2117–25
Done SH, Clayton-Jones DG and Pprice EK (1970) Tracheal collapse in the dog: a review of the literature and report of two new cases. Journal of Small Animal Practice 11: 743–750
Johnson LR and Pollard RE (2010) Tracheal collapse and bronchomalacia in dogs: 58 cases. Journal of Veterinary Internal Medicine 24: 298–305
KiChang L, KyungJin S, HoJung C, JinYoung H, JooHyun J, JinHwa C, JungHee Y and MinCheol C (2004) Retrospective study of tracheal collapse 99 cases diagnosed by radiography in dogs (2002-2003). Journal of Veterinary Clinics 21: 276–279
Maggiore A Della (2014) Tracheal and airway collapse in dogs. The Veterinary clinics of North America. Small Animal Practice 44: 117–127
Meyers-Wallen VN (2003) Ethics and genetic selection in purebred dogs.. Reproduction In Domestic Animals 38: 73–6
Tangner CH and Hobson HP (1982) A Retrospective Study of 20 Surgically Managed Cases of Collapsed Trachea. Veterinary Surgery 11: 146–149
White RAS and Williams JM (1994) Tracheal collapse in the dog - is there really a role for surgery? A survey of 100 cases. Journal of Small Animal Practice 35: 191–19
© UFAW 2016
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http://depositphotos.com/13265541/stock-photo-yorkshire-terrier-in-city-park.html ©Depositphotos.com/tandemich
