Fact Sheet Dog Breed Chihuahua

More pictures can be found here (click on picture):

 3. Problems/syndromes that may occur in the breed

Of several problems and possible diseases that occur in this breed, only the most important defects typical of the breed are listed here.

The following breed-typical defects or common problems/health disorders and dispositions* are known in the Chihuahua:

* (please also refer to the existing information sheets on individual defects such as brachycephaly, color dilution alopecia (CDA), fact sheet no. 34 on the Cavalier King Charles Spaniel breed (on CM/SM))

• Patellar luxation
• Mitral valve disease
• Chiari-like malformation/syringomyelia
• Eye diseases 
• Brachycephaly
• BOAS (brachycephalic obstructive airway syndrome)
• Hydrocephalus
• Skin diseases

4. Other problems that may occur frequently

In the veterinary literature, in addition to the breed-typical defects listed under point 3, there are references to the occurrence of the following problems, which are not described further below, as no definitive conclusions can yet be drawn from the known prevalences and breeders, breeding clubs and associations do not provide any prevalence data collected under scientific conditions. In these cases, however, the following statement by Hale (2021) applies: „The absence of evidence is not the evidence of absence.“ 

• Atlantoaxial subluxation/instability
• Intervertebral disc disease (IVDD)
• Chondrodysplasia
• Dystocia
• Demodicosis
• Eclampsia/puerperal tetany
• Epilepsy
• Extrahepatic portosystemic shunt
• Gallbladder mucocele
• Hemophilia
• Keratoconjunctivitis sicca
• Cryptorchidism
• Legg-Calvé-Perthes disease
• Necrotizing meningoencephalitis
• Neuroaxonal dystrophy
• Neuronal ceroid lipofuscinoses (NCL)
• Periodontal diseases
• Persistent ductus arteriosus (PDA)
• Persistent fontanelles
• Pulmonary stenosis
• Pattern baldness
• Tracheal collapse
• Urolithiasis

5. Symptoms and pathological value of the most important defects mentioned above under point 3: Significance/impact on the physical/psychological well-being (burden) of the defect in the individual animal and classification in burden category*

* The individual breeding-related defects are assigned to different burden categories (BC) depending on their degree of severity. The overall burden category is based on the most severe defect found in the individual animal. The BC system used here is a further development based on the Swiss model (i.e. the assessment may deviate from the Swiss classification) and is still being developed and is the result of an animal welfare assessment. For this reason, the BC values used here are to be regarded as provisional and provide initial guidance until a transnational definition is established. For example, functional impairments of sensory organs are assigned to burden category 2-3 depending on their severity.

In Switzerland, the burdens that can be caused by breeding characteristics are divided into four categories (Art. 3 TSchZV, Switzerland).
The overall assessment of an animal’s suitability for breeding is based on the category of the trait or symptom that has the greatest negative impact on the animal (Art. 4 TSchZV, Switzerland).

Category 0 (no burden): Breeding is permitted with these animals.

Category 1 (mild burden): A mild burden exists if a burdenful expression of traits and symptoms in pets and farm animals can be compensated for by appropriate care, husbandry or feeding, without interventions on the animal and without regular medical care measures.

Category 2 (medium burden): These animals may only be bred if the breeding objective includes ensuring that the burden of the offspring is below that of the parent animals.

Category 3 (severe burden): These animals may not be used for breeding.

Note in advance on the breeding-related defects that may be found in this breed: Breeding and showing are now international. As no reliable prevalence figures on defect characteristics are provided by breeders, breeding clubs and associations, the available international scientific literature is evaluated.

Patellar luxation

Physical:
Chihuahuas have an increased risk of patellar luxation, which occurs almost exclusively medially. Depending on the study, the risk of the condition was 2.8 to 8.9 times higher for Chihuahuas. A study of 7,024 Chihuahuas found a prevalence of patellar luxation of 23%. According to study results, female Chihuahuas are affected more often than males.

The Breed Report by the Swedish animal health insurance company AGRIA found that Chihuahuas have an almost 4 times higher relative risk of developing patellar luxation compared to the average of all other dog breeds for the period from 2016 to 2021. According to the Chihuahua Breed Summary Report by the Orthopedic Foundation for Animals (OFA), 6.2% of animals had patellar luxation in 2024.

Various publications refer to patellar luxation as a common knee joint problem, especially in small dog breeds. Patellar luxation is described as a so-called developmental disease that is not present at birth but only manifests itself in the early years of life. This suggests that the development of the disease is not due to a single factor, but rather to a complex interaction of genetic (hereditary) predispositions and environmental influences. Environmental factors can include, for example, biomechanical stress, growth conditions, or poor posture, while hereditary factors relate to genetic predispositions for an unstable patella or anatomical peculiarities. The combination of these aspects ultimately leads to the development of patellar luxation at a young age. The heritability for patellar luxation is 0.24-0.25, with a study from Finland giving a value of 0.22. In patellar luxation, the kneecap is displaced medially or laterally from its normal position in the trochlear sulcus of the femur. This occurs mainly during movement. Various authors describe that the clinical symptoms can vary greatly from dog to dog. Patellar luxation in dogs is classified into four degrees of severity. In grade 1, the animals are usually asymptomatic. In grade 2, dogs show characteristic hopping (lameness, especially intermittent) and occasionally walk on three legs. As the severity increases, so do the symptoms, such as lameness on the affected side with occasional lifting of the limb and pain. Typically, affected dogs extend the limb backward so that the patella can reluxate. Both unilateral and bilateral patellar luxations affect the movement of the front and hind limbs. When walking and trotting, it can be observed that the range of motion in the hip and tarsal joints is restricted.

Psychological:
The dogs suffer from lameness, later also from osteoarthritis and pain, which can negatively affect many behaviors and thus impair their well-being.

Burden category: 2

Mitral valve disease

Physical:
Chihuahuas are predisposed to mitral valve disease. Depending on the study, the prevalence of the disease ranges between 2.2% and 2.5%. It has been found that purebred dogs with degenerative mitral valve insufficiency have a 1.86 times higher risk of death compared to mixed-breed dogs. The results of the study suggest that Chihuahuas may be more susceptible to serious consequences of the disease and therefore require more intensive medical care.

Degenerative mitral valve disease causes mitral valve insufficiency, in which the valve between the left atrium and left ventricle no longer closes properly. This impairs forward stroke volume and causes volume overload on the left side of the heart. This ultimately leads to the activation of compensatory mechanisms. Initially, clinical signs only occur during cardiac stress, and dogs develop a cough as the disease progresses. As the disease progresses, heart rate and heart rate variability gradually change, and animals may develop shortness of breath and syncope (brief fainting spells).

Psychological:
Impaired exercise capacity restricts the dogs in their species-typical behavior. Difficulty breathing during exertion can also cause anxiety because the dogs perceive this situation as life-threatening. These anxiety states are regarded as suffering, as they significantly impair the well-being of the animals.

Burden category: 2-3 depending on the degree of severity

Chiari-like malformation/Syringomyelia
(see also factsheet no. 34 Dog Breed Cavalier King Charles Spaniel)

Physical:
Chiari-like malformation occurs frequently in small breeds such as Chihuahuas. Chihuahuas are also affected by syringomyelia. Compared to mixed-breed dogs, Chihuahuas have a 7.4 times higher risk of developing Chiari-like malformation and syringomyelia. The changes to the skull and its structures that are also typical of Chihuahuas are associated with the development of Chiari-like malformation and syringomyelia. Rusbridge et al. (2018) describe the bony and parenchymal changes that can be summarized under the term Chiari-like malformation. It is assumed that premature closure of the cranial sutures leads to narrowing in the rostrotentorial region (the tentorium is a dural fold that separates the cerebellum from the cerebrum), which can cause herniation of the hindbrain. The situation is further complicated by a deformation of the connection between the skull and cervical spine, including changes in the alignment of the dens axis, a reduced distance between the atlas and the skull, and a loss of the cisterna magna, an important cerebrospinal fluid space. This leads to compression of the brain and spinal cord and often results in herniation of the metencephalon. In some affected animals, however, there is a deepening of the cerebellum (cerebellar indentation) with displacement of the cerebellum.

Dogs with a Chiari-like malformation and syringomyelia may exhibit persistent scratching episodes of the ears, shoulders, or anterior thoracic spine with or without skin contact (phantom scratching), facial rubbing, spinal pain, hyperesthesia in the cervical and cranial regions, vocalization, and gait abnormalities such as lack of coordination or weakness. Other neurological symptoms are possible. Dogs may also show signs of neuropathic pain. Dogs are sometimes less active and their sleep phases are interrupted. Similar symptoms occur in Chiari-like malformation even without syringomyelia, highlighting the importance of abnormalities of the craniocervical junction. However, these abnormalities can still be a risk factor for syringomyelia. Based on studies conducted, Rusbridge (2020) concludes that the first symptoms of Chiari-like malformation usually appear in the first years of life.

A common consequence of Chiari-like malformation is syringohydromyelia/syringomyelia. Syringomyelia involves fluid-filled cavities in the spinal cord that can exert pressure on the spinal cord. The exact causes are not fully understood. Among other things, it is suspected that it is due to impaired flow of cerebrospinal fluid (CSF). Syringomyelia often only occurs at a later age, and most animals are not younger than five years old. Syringomyelia is a predisposing factor for the presence of neuropathic pain.

Persistent fontanelles were frequently observed in Chihuahuas with clinical symptoms of syringomyelia/Chiari-like malformation. An association between the two abnormalities is assumed.

Psychological:
Affected dogs are restricted in their behavior and well-being due to motor impairments and neurological deficits. Pain also has a negative effect on the animals. Anxiety and fear, which can be promoted by neuropathic pain, severely restrict the quality of life. Even touching and lifting can cause vocalizations (howling) because they are painful. Reduced activity and impaired or interrupted sleep lead to suffering.

Burden category: 3

Eye diseases 

Physical:
In a retrospective study conducted at a North American university hospital, Chihuahuas showed an increased prevalence of primary cataracts (1.84%) compared to mixed-breed dogs. The incidence of cataracts was particularly high in the group of 10- to 15-year-old Chihuahuas. Overall, however, the prevalence of cataracts has declined over the last 10 years of data collection. The Genetics Committee of the American College of Veterinary Ophthalmologists also reports a prevalence of cataracts in Chihuahuas of 2.1%. In a retrospective study, the risk of Chihuahuas developing cataracts was 1.3 times higher than in the reference population.

Chihuahuas are also among the dog breeds most commonly affected by ulcerative keratitis. It is believed that differences in the width of the palpebral fissure and the shape of the skull in these dogs may have an impact on the health of their ocular surface. These effects could manifest themselves in changes in blink rate, friction on the surface of the eye, the composition of tear fluid, or slight pathological changes in the cornea. Such factors could therefore increase the risk of eye problems or impair the surface of the eye. The disease can lead to loss of the eyeball.

Genotyping provides clues to the genetic factors involved in the development of progressive retinal atrophy in Chihuahuas. The late form of PRA often occurs in Chihuahuas, as the disease is not clinically detected in most affected dogs until they are 3 to 6 years of age or older. According to the Genetics Committee of the American College of Veterinary Ophthalmologists (ACVO), progressive retinal atrophy (PRA) is a degenerative disease of the retinal photoreceptor cells that progresses to blindness. PRA encompasses a group of diseases with similar clinical manifestations and is divided into different forms based on the age of onset, pathological features, and genetic mutations in specific genes. Progressive rod-cone degeneration (PRCD) is one form of this disease. It usually occurs in middle to old age and causes degeneration of the photoreceptors. The degeneration of normally developed photoreceptors is characterized by a slow death of the photoreceptor cells. The first clinical signs are night blindness, followed by day blindness as the disease progresses.

Corneal dystrophy in Chihuahuas is described as a primary endothelial disease that leads to progressive and permanent corneal edema. Chihuahuas are among the breeds that are overrepresented in this disease. The disease occurs in older dogs, usually between the ages of 6 and 13, with an average age of about 9.5 years. The corneal edema initially begins without visible symptoms in the dorsal, temporal area of the cornea of one eye and slowly spreads inward until eventually the entire cornea is affected. The disease is usually bilateral.

Psychological:
Eye diseases can cause pain in animals and, depending on the severity, can impair vision. Ulcerative changes of the cornea have a strong influence on the well-being of the animals, as they can lead to pain, uveitis, perforation and even impaired vision and loss of the eye. Dogs with severely impaired vision or blindness are barely able to recognize or use body signals such as posture, tail position or eye, head and mouth signals. This can lead to behavioral changes, anxiety and insecurity.

Burden category: 2-3

Brachycephaly
(see also Fact Sheet No. 8 Dog Brachycephaly and other fact sheets on brachycephalic breeds)

Physical:
Geiger et al. (2021) summarize the breeding-related changes to the skull associated with brachycephaly in their detailed overview. Characteristic features include a short, round skull with a flat muzzle and short nose. While some dog breeds have a curved muzzle in addition to shortened bones, this type of airorhynchy is not present in breeds such as the Chihuahua, as the angle between the base of the skull and the palate is less than 180° on average. In a study from the UK, the Chihuahua was one of the most common brachycephalic breeds within the population studied, accounting for 22.91%. The health status of brachycephalic dog breeds is limited compared to non-brachycephalic breeds. Brachycephalic dogs fall ill more often and have a higher risk of various diseases. The life expectancy of brachycephalic breeds is reduced compared to mesocephalic and dolichocephalic dogs. The reasons for this are thought to be the predispositions associated with brachycephaly, such as BOAS, spinal disorders, and other abnormalities.

Psychological:
Compared to breeds without an extreme skull shape, brachycephalic breeds appear to be significantly more frequently affected by various diseases and have a lower life expectancy. Many behaviors and areas of the animal’s life are negatively affected by brachycephaly and the resulting diseases. Breathing difficulties and thus anxiety can occur during feed intake. Affected animals usually need a longer recovery phase after active phases. Playing with conspecifics may be restricted. Overall, it can therefore be assumed that the quality of life is significantly reduced.

Burden category: 3

BOAS (brachycephalic obstructive airway syndrome)
(see also information sheets for other brachycephalic breeds)

Physical:
Review articles such as that by Meola (2013) describe the anatomical and physiological basis of brachycephalic obstructive airway syndrome (BOAS) and its consequences. Primary components include congenital anatomical features such as stenotic nostrils, an elongated soft palate, a hypoplastic trachea, and nasopharyngeal turbinates. Increased turbulence and increased airway resistance can lead to the development of secondary changes. These include palate and laryngeal edema, swelling, protruding saccula and tonsils, and laryngeal collapse, all of which can lead to life-threatening respiratory impairment.

A contributing factor to BOAS is brachycephaly. Due to their shortened skull, brachycephalic dogs have a relatively elongated soft palate compared to non-brachycephalic dogs. In addition, the soft palate is thickened. The space or volume of the nasopharynx, on the other hand, is significantly reduced. The risk of BOAS decreases with increasing relative muzzle length. With a smaller craniofacial ratio (division of muzzle length by skull length), as is common in brachycephalic breeds, the risk of BOAS increases compared to breeds with other skull shapes. Other risk factors for development or worsening can include neck circumference, obesity, and neutering. Surgical correction of the anatomical changes may be indicated.

Affected dogs show typical snoring noises, exercise intolerance, dyspnea, choking, regurgitation, vomiting, stridor, and syncope. In addition, there is impaired thermoregulation.

Note: Contrary to the widespread belief that only moderate restriction of respiratory function (e.g., Cambridge test result grade 1) would justify the animal’s suitability for breeding or exhibition, this assessment is not comprehensible from a medical point of view, as it is a pathological finding caused by anatomical changes, with a usually progressive course.

Psychological:
Various surgical interventions may be indicated in BOAS and serve to correct the airway obstruction and improve the dog’s quality of life. The post-operative (recovery) phase is particularly risky and requires intensive observation and care. However, the evaluation of various studies showed that a complete resolution of the problems is not always achievable. The clinical symptoms listed above significantly impair the species-typical behavior and well-being of the animals for the rest of their lives.

Burden category: 3

Hydrocephalus

Physical:
Various publications describe a high incidence of congenital hydrocephalus in Chihuahuas. Affected animals may have an altered skull shape or an open fontanelle. The animals may show neurological deficits and changes in mental state, ranging from depression to hyperexcitability. Consciousness or the function of sensory organs (vision and hearing) may be impaired. Affected dogs move in an uncoordinated manner, circle, and may show signs of central nervous system disorders (seizures). Dilated and rigid pupils, blindness, and strabismus are also possible. Symptoms may worsen as the disease progresses. Some animals show no clinical signs.

Congenital hydrocephalus also occurs as a result of a variety of abnormalities of the nervous system, including Chiari-like malformation (see there).

Psychological:
Due to the highly variable clinic, the effects on the animals are very different and depend on the respective symptoms. These can be stressful, overexcited or depressive states as well as restrictions in mobility, which in turn can have an impact on behavior.

Burden category: 3

Skin diseases
(see also leaflet no. 25 Dog Color Dilution Alopecia)

Physical:
Hobi et al. (2023) describe in a review paper that melanin precursors with cytotoxic properties and abnormal pigment clumps in the epidermis, hair shaft, hair follicle, and hair matrix lead to bulging and breakage of the hair cuticle, which can ultimately result in alopecia. Chihuahuas are predisposed to the described color dilution alopecia (CDA). The affected areas experience progressive hypertrichosis, alopecia, and dandruff, as well as folliculitis and furunculosis. There is no known specific treatment for color dilution alopecia. Affected dogs should not be exposed to intense UV light. In addition, special care must be taken to ensure that affected dogs do not suffer skin injuries.

Psychological:
In Color Dilution Alopecia, dogs suffer from the painful secondary infections described above and from freezing in cold temperatures, from which a coat appropriate to the species normally protects dogs. 

Burden category: 2

Life expectancy and mortality

The life expectancy of brachycephalic breeds is shorter than that of mesocephalic and dolichocephalic breeds. The reasons for this are diseases such as BOAS (brachycephalic obstructive airway syndrome), spinal disorders, and other abnormalities that occur more frequently in brachycephalic dog breeds. Although small dog breeds generally have a longer life expectancy than large breeds, the average life expectancy of a Chihuahua is only about 7-8 years. Data from AGRIA Insurance from 2016 to 2021 show that Chihuahuas died or had to be euthanized due to heart disease and neurological symptoms. The average age of these dogs at the time of death was around 8 years. A North American study documented the most common causes of death in different dog breeds over a period of 20 years. The Chihuahua was among the 5 breeds with the highest relative proportion of cardiovascular causes of death. Another retrospective epidemiological evaluation of data on Chihuahuas in the UK found that heart disease was the underlying and thus the most common cause of death in 18.8% of deceased animals.

Behavioral problems due to short stature in „toy breeds“

Due to their small size, small dogs are very sensitive. Fractures can occur after a slight fall or jump, from being stepped on or sat on, or even from playing with other dogs. To protect them, they are often carried in bags or strollers. Small dogs are more likely to react aggressively when provoked, which in turn can provoke larger dogs—with the associated risks. If a large dog bites, the small dog can be seriously injured or even killed. However, it is unclear whether this behavior is due to genetic factors, learned behavior, or a combination of both. Some owners tolerate different behaviors in small and large dogs. For example, aggressive or jumping behavior is usually discouraged in a large dog, while the same behavior in a small dog is often considered cute and encouraged. Small dogs are often carried instead of walking, may not respond to commands, and are overly protected, which can hinder their development. Genetic factors may also play a role. Lighter dogs are often described as excitable, hyperactive, and energetic. Behaviors such as urinating when left alone, separation issues, clinginess, or begging are more common in smaller breeds and may be childlike behaviors or expressions of neediness.

Animal ethical evaluation of the problem of torture breeding in the Chihuahua

Based on the facts stated in this information sheet, which list the probability of a number of breeding-related defects in burden categories 2-3 (medium to severe burden) and 3 (severe burden), it can be concluded from an animal welfare perspective that further breeding with animals of this breed affected by these defects is highly problematic, as a breeder must assume that animals brought into the world through their breeding will endure or suffer significant and lasting restrictions on their well-being and pain. This is already unacceptable if at least one of the breeding-related defects listed in the information sheet in question occurs in the burden categories 2-3 in at least one of the animals bred by the breeder in a foreseeable manner, whereby “foreseeable” hereditary changes in the offspring are also present if they are only expected to occur after a generational leap in later generations.

Conclusion: Toy breeds, such as the Chihuahua, are often unable to live out their species-specific behavioral repertoire for the reasons mentioned above.

6. Heredity, genetics, known genetic tests if applicable, average genomic inbreeding coefficient (COI) for the breed if applicable

Patellar luxation
Two genetic variations (SNPs) within the DAG1 gene on chromosome 20 are strongly associated with patellar luxation in Chihuahuas: SNP1UBC811 and SNP2UBC811. 

Mitral valve disease
The exact genetic background of the disease is not yet fully understood. So far, various genes and microRNAs have been discovered whose expression differs in healthy and diseased dogs and which could therefore play a role.

Brachycephaly
The responsible gene or genes are not fully understood. Due to the genetic complexity, it is assumed that various chromosomes have an influence. There is a strong association with the CFA1 gene.

Hydrocephalus
The Chihuahua is one of the most frequently affected breeds, which is why genetic factors are suspected in the development of hydrocephalus. It is not clear whether the higher prevalence of hydrocephalus is due to a genetic abnormality that directly affects the central nervous system or is more related to the abnormal head morphology.

Skin diseases (Color Dilution Alopecia (CDA))

Dilution is caused by different genetic variants (allele d1, d2 and/or d3 and probably other variants that have not yet been identified by molecular genetics) in the MLPH gene and follows an autosomal recessive pattern of inheritance. However, the causative variant of CDA has not yet been identified by molecular genetics. Therefore, a dilute dog without CDA cannot be distinguished from a dilute dog with CDA by genetic testing. Affected dogs should not be used for breeding.

Other genetic tests available for the breed

• Chondrodysplasia and dystrophy
• Degenerative myelopathy (DM) exon 2
• Hyperuricosuria
• Lafora epilepsy
• Macrothrombocytopenia
• Malignant hyperthermia
• Neuronal ceroid lipofuscinosis (NCL)
• Progressive retinal atrophy (prcd-PRA)

The basis of responsible breeding is not only the careful diagnosis of individual animals, including the assessment of the exterior and behavioral characteristics of breeding partners before the first breeding, but also the use of modern molecular genetic diagnostics. Within a screening, this should be used not only to identify trait or gene carriers, but also to determine the degree of inbreeding of the individual animal. Laboratories now offer so-called “matching tools” or “mating scores” that breeders can use to identify suitable breeding partners, while at the same time preventing the mating of animals with the same risk factors. Various specialized laboratories offer appropriate advice for breeders.

7. Diagnosis – necessary examinations before breeding or exhibitions

Caution: Invasive examinations that are stressful for the animal should only be carried out in justified cases of suspicion in breeding animals and not if visible defects already lead to a ban on breeding and showing.

Patellar luxation

Clinical and radiological examinations are suitable for diagnosing and assessing the degree of luxation. In the orthopedic examination, the gait is evaluated and the range of motion and the patella are assessed. Measurements can also be used to assess and compare the morphological deviations.

Mitral valve disease

During a clinical examination, the presence of a characteristic murmur can be detected by auscultation even in the early stages of mitral valve disease. In addition to checking clinical signs, echocardiographic examinations and X-rays can be used for diagnosis. Speckle-tracking echocardiography (STE) can be used to measure parameters that indicate whether an existing mitral regurgitation is progressing and overloading the heart. 

Chiari-like malformation/syringomyelia

For diagnostic purposes, a detailed medical history is taken and a clinical and neurological examination is performed. Dermatologic and orthopedic examinations are performed to rule out other causes for the scratching and gait abnormalities, for example. More precise assessments can be made using imaging techniques such as MRI or CT.

Eye diseases

If an eye disease is suspected, a complete ophthalmologic examination is performed. Depending on the suspected diagnosis, a Schirmer tear test, tonometry, ophthalmoscopy and other diagnostic procedures can provide information. 

The presence of a corneal ulcer can be diagnosed with a digital photo-slit lamp and topical administration of fluorescein stain.

An electroretinogram can detect progressive retinal atrophy before it becomes clinically apparent. This procedure is not part of a routine eye examination. A DNA test for PRA is available.

Brachycephaly 

In addition to the adspectory examination to determine changes in head shape, nostrils and jaw, further specialist veterinary examinations, imaging procedures to examine the head and, in some animals, the skeletal system are usually necessary in order to provide the respective animal with any necessary medical treatment. Imaging such as endoscopy can be used to detect stenosis, narrowing of the nasal vestibule, overlength and thickening of the soft palate, changes in the trachea and excessive tissue in the nasopharynx/muzzle.

Brachycephaly can be quantified on the basis of the craniofacial ratio using tested measurement methods..For this purpose, the muzzle length is divided by the skull length. The measurements can also be made on X-ray images of the skull.

BOAS (brachycephalic obstructive airway syndrome)

Diagnosis is based on owner reports, clinical examination and diagnostic imaging. Imaging techniques such as MRI allow a more precise assessment of the upper airways. In addition to the narrowed nostrils, inspection may reveal some respiratory effort with abdominal breathing. While snoring is most likely caused by air turbulence in the oro-pharyngeal region, the high-pitched noise associated with extreme inspiratory effort is due to severe airway compromise as the turbulent air passes through the collapsed larynx or nasopharynx.

Hydrocephalus

Diagnosis is based on clinical examination and imaging techniques such as X-ray, CT and/or MRI.

Skin diseases 

Depending on the suspected diagnosis, the medical history and clinical examination are followed by further dermatological examinations.

A suspected diagnosis of color dilution alopecia can be made on the basis of the phenotype. Dilution (possibly confirmed molecularly by the finding d/d at the dilution gene locus) in combination with hair loss, especially on the trunk (CDA) and hairless color plates on the trunk on an unchanged white (unpigmented) background are pathognostic. The final diagnosis is made on the basis of the histopathological findings of a skin biopsy. A DNA test can also be carried out.

8. Necessary or possible orders from an animal welfare perspective

Decisions on breeding or exhibition bans can be made in connection with the burden category (BC). Depending on the severity and findings, the decisive factor for a breeding ban may be the most severe finding, i.e. the finding that most affects the animal and its classification in one of the burden categories (BC), or also the assessment of the correlation if there are many individual breeding-related defects or predispositions typical of the breed. The individual genomic inbreeding coefficient of an animal and its capacity as a carrier of risk genes should also be taken into account. 

In general, attention should also be paid when breeding Chihuahuas:

In addition to considering external, anatomical and functional characteristics as well as the behavior of both breeding partners, the possibilities of breeding hygiene advice at the molecular genetic level should be used and in particular the genetic inbreeding coefficient, the heterozygosity value and the Dog Leukocyte Antigens (DLA) for the breed should be determined. Increasingly, so-called matching tools/scores can also facilitate the selection of suitable breeding partners.

a) Orders that appear necessary

 Breeding ban according to § 11b TierSchG for animals with hereditary/breeding-related defects of burden categories 2 and 3, at least with

• Patellar luxation
• mitral valve disease
• Chiari-like malformation/syringomyelia
• Eye diseases (cataract, ulcerative keratitis (corneal ulceration), progressive retinal atrophy (PRA), corneal dystrophy)
• Brachycephaly
• BOAS (brachycephalic obstructive airway syndrome grade 1 and above)
• Changes in the skeletal system: Head (skull)
• Hydrocephalus
• Skin diseases (Color Dilution Alopecia (CDA))

Exhibition ban according to § 10 TierSchHuV at least for characteristics/symptoms of burden category 3.

b) Possible orders

1. Order for permanent surgical infertility (sterilization/castration) in accordance with Section 11b (2) TierSchG
2. Ordering genetic tests to determine the genomic inbreeding coefficient and heterozygosity value of both animals intended for breeding, if applicable
3. Use of breeding hygiene advice and, if necessary, so-called matching tools to avoid unsuitable matings.
   

c) Inquiries and orders (as part of a risk assessment measure) before a breeding license is issued:

• Breeding association/club
• Breeder
• Population size of the breed in the club/association
• Currently valid breed standard and breeding regulations
• Requirements in the standard / anatomical characteristics that predispose to diseases
• Genomic (not calculated) inbreeding coefficient of the animal/breed
• Diversity (HET, DLA)
• Average age reached
• Most frequent cause of death
• Average litter size
• Pup mortality rate
• Total number of veterinary interventions for obstetrics / caesarean sections

 Examinations

• Voluntary examinations

• Mandatory examinations to be carried out before use for breeding

 Genetic tests (which are available and verified for the breed?)

• Voluntary genetic tests
• Mandatory genetic tests to be carried out before use in breeding

Please note:

Measures taken by the competent authority must be recognizably suitable to avert future harm to the animal concerned and/or its offspring. With regard to the type and depth of processing of orders and breeding or exhibition bans, it is always a case-by-case decision at the discretion of the competent authority, taking into account the current legal standards and the circumstances found on site.

9. General animal welfare assessment

a) Germany

From a legal point of view, dogs with the defects/syndromes described above are classified as products of torture breeding in accordance with § 11b TierSchG.

Justification:

According to § 11b TierSchG, it is prohibited to breed vertebrates if breeding knowledge indicates that, as a result of breeding, the offspring or progeny will have, among other things

• body parts or organs for species-appropriate use are missing for hereditary reasons or are unsuitable or deformed, resulting in pain, suffering or damage (Section 11b para. 1 no. 1 TierSchG) or
• keeping the animal is only possible with pain or avoidable suffering or leads to damage (Section 11b (1) No. 2 c) TierSchG).

Pain is defined in animals as an unpleasant sensory perception caused by actual or potential injury that triggers motor or vegetative reactions, results in learned avoidance behavior and can change potentially specific behaviors (Hirt/Maisack/Moritz/Felde, TierSchG, Kommentar 4th ed. 2023 § 1 para. 12 mwN; basically also Lorz/Metzger TierSchG 7th ed. § 1 para. 20).

Suffering is any impairment of well-being not already covered by the concept of pain, which goes beyond simple discomfort and lasts for a not insignificant period of time (Hirt/Maisack/Moritz/Felde Tierschutzgesetz Kommentar 4th ed. 2023 § 1 para. 19 mwN; Lorz/Metzger, TierSchG Komm. 7th ed. 2019 § 1 para. 33 mwN). Suffering can also be physically and psychologically impairing; fear in particular is classified as suffering in the commentary and case law (Hirt/Maisack/Moritz/Felde Section 1 TierSchG para. 24 with further references; Lorz/Metzger Section 1 TierSchG para. 37). Normal behavior is an indication of well-being and health; conversely, restricted movement behavior, for example, is an indication of impaired well-being and thus of suffering (Hirt/Maisack/Moritz/Felde § 1 TierSchG para. 20).

Damage occurs when the physical or mental condition of an animal is temporarily or permanently altered for the worse (Hirt/Maisack/Moriz/Felde TierSchG Komm. 4th ed. 2023 § 1 para. 27 mwN; Lorz/Metzger TierSchG Komm. 7th ed. 2019 § 1 para. 52 mwN), whereby completely minor impairments based on a physical or psychological basis are not taken into account. „The target condition of the animal is assessed on animals of the same species. The absence of body parts is regularly assessed as damage in the commentary literature“ (VG Hamburg decision of 4.4.2018, 11 E 1067/18 para. 47, also Lorz/Metzger TierSchG Komm. § 1 para. 52).

The breeding of Chihuahuas constitutes torturous breeding due to individual or multiple pain, suffering or damage as described in detail under point 5:

• Damage to the skeletal system (head, spine, limbs)
• Brachycephaly and brachycephalic airway syndrome (BOAS) and associated suffering
• Syringomyelia/Chiari-like malformation
• Heart disease
• Eye disorders and associated pain and damage
• Skin diseases and associated pain and suffering

Section 11b para. 1 TierSchG stipulates that the breeder must have breeding knowledge that a consequence specified in Section 11b para. 1 will occur as a result of breeding. According to the explanatory memorandum to the law, this is to be based on „scientifically sound knowledge, i.e. knowledge that can be expected of a breeder with average knowledge“ (cf. BT-Drs. 17/10572, p. 31). Breeding knowledge exists if there is certain experience with the breeding of certain animal breeds based on generally accessible sources (in particular statements from breeding associations, specialist journals, books and veterinary reports as well as the BMEL’s expert opinion on torture breeding), which, due to their consistency, can be condensed into almost certain knowledge (Lorz/Metzger, Kommentar zum TierSchG § 11b TierSchG para. 11). The torture breeding report of the BMEL explicitly mentions the Chihuahua under point 2.1.1.2 among the affected breeds for the torture breeding trait brachycephaly.

The breeding ban in Section 11b TierSchG applies regardless of whether the breeder himself has recognized the possibility of harmful consequences, but depends on whether the respective knowledge and experience can be expected from a careful breeder of the respective animal species (see Hirt/Maisack/Moritz, Tierschutzgesetz, Kommentar, § 11b TierSchG Rn. 6).

 – An important indication of a hereditary defect is that a disease or behavioral deviation occurs more frequently in related animals than in the overall population of the dog species. The fact that the breed or population has proven to be viable over a longer period of time is not an argument against damage (see Lorz/Metzger Kommentar zum TierSchG § 11b Rn. 9).

 – The prohibition applies regardless of the subjective facts, i.e. regardless of whether the breeder himself recognized or should have recognized the possibility of harmful consequences. Due to this objective standard of care, the breeder cannot invoke a lack of subjective knowledge or experience if the respective knowledge and experience can be expected from a careful breeder of the respective animal species (see Hirt/Maisack/Moritz, Tierschutzgesetz, Kommentar 4th ed. 2023, § 11b TierSchG para. 6).

– Hereditary changes in the offspring are also foreseeable if it is uncertain whether they will only occur after a generation jump in later generations (cf. Goetschel in Kluge § 11b para. 14).

b) Austria

Dogs with the defects/syndromes described above are to be classified as torture breeding in Austria according to § 5 TSchG

In particular, Section 5 of the Austrian Animal Welfare Act is violated if „breeding is carried out which is foreseeable to be associated with pain, suffering, harm or fear for the animal or its offspring (torture breeding), so that as a result, in connection with genetic abnormalities, in particular one or more of the following clinical symptoms occur in the offspring not only temporarily with significant effects on their health or significantly impair physiological life courses or cause an increased risk of injury“.

Shortening of the facial skull: Breeding with dogs that suffer from a massive shortening of the facial skull and the associated problems or are genetically predestined for this is to be qualified as torture breeding if, among other things, the following symptoms listed in § 5 are realized: respiratory distress, malformation of the dentition.

Eye diseases: Breeding with dogs that suffer from pathological changes of the eyes or are genetically predestined is to be qualified as torture breeding if one of the following symptoms listed in § 5 is realized: blindness, exophthalmos, restriction of physiological functions due to inflammation or malformation of the eyes or their appendages.

Cardiovascular diseases: Due to the wording „in particular“ chosen for the list of possible defects, heart disease in the offspring is also one of the clinical symptoms that occur not only temporarily with significant effects on their health and therefore fall under Section 5 (1) TSchG. The shortening of life expectancy is also covered by the term „significant impairment of physiological life cycles“.

Syringomyelia/Chiari-like malformation: Breeding with dogs that have a malformation of the skull in the form of a Chiari-like malformation and/or syringomyelia, or that are genetically predestined for this, is to be qualified as torture breeding if one of the following symptoms listed in § 5 is realized: neurological symptoms, malformations of the skull (e.g. persistent fontanelles, extremely thin skull bones).

Patellar luxation: Breeding with dogs that have a patellar luxation or are genetically predisposed to it is to be qualified as torture breeding if one of the following symptoms listed in § 5 is present: movement abnormalities, lameness.

c) Switzerland

Anyone wishing to breed with an animal that exhibits a trait or symptom that may lead to moderate or severe burden in connection with the breeding objective must first have a burden assessment carried out. Only hereditary stresses are taken into account in the burden assessment (see Art. 5 of the FSVO Ordinance on Animal Welfare in Breeding (TSchZV). Dogs with defects that can be assigned to burden category 3 are subject to a breeding ban in accordance with Art. 9 TSchZV. It is also prohibited to breed with animals if the breeding objective results in category 3 defects in the offspring. Animals in category 2 may be used for breeding if the breeding objective is for the offspring to be less affected than the parents (Art. 6 TSchZV). Annex 2 of the TSchZV lists characteristics and symptoms that can lead to moderate or severe burden in connection with the breeding objective. Movement anomalies, degenerative joint changes, skull deformities with disabling effects on the ability to breathe, the position of the eyes, the position of the teeth and the birth process, herniated discs, eye malfunctions and persistent fontanelles are explicitly mentioned. In addition, individual breeding forms are expressly prohibited in accordance with Art. 10 TSchZV. According to lit. c, dwarf dogs that weigh less than 1500 grams when fully grown fall under this ban. In other cases, however, a breeding ban is only imposed on a case-by-case basis. Animals that have been bred on the basis of impermissible breeding objectives may not be exhibited (Art. 30a para. 4 let. b TSchV).

d) Netherlands

According to Article 3.4 „Breeding with domestic animals“ of the Animal Keeper Decree, it is prohibited in the Netherlands to breed with domestic animals in a way that is detrimental to the well-being and health of the parent animals or their offspring.

In any case, breeding must, as far as possible, prevent

a) serious hereditary defects and diseases are passed on to the offspring or can occur in them;

b) external characteristics are passed on to the offspring or can develop in them which have harmful consequences for the welfare or health of the animals.

The following hereditary diseases or abnormalities according to Article 3.4. are realized in the Chihuahua: brachycephaly, diseases of the eye, abnormalities of the skull, heart valve diseases.
The following harmful external characteristics can be passed on to the offspring of Chihuahuas: short muzzle, short stature (miniature breed).

It is prohibited in the Netherlands in accordance with Article 3.4. „Breeding with domestic animals“ of the Animal Keeper Decree and Article 2 sentence 1 of the Decree „Breeding with brachycephalic dogs“, it is prohibited to breed dogs whose muzzle is shorter than one third of the skull length and which exhibit other of the above-mentioned related problems: produce a secondary sound when breathing at rest; have moderate to severe narrowing of the nostrils; hair that touches or could touch the cornea or conjunctiva and signs of inflammation in one or both eyes related to corneal irritation; an eye with whites visible in two or more quadrants; an eyelid that cannot be fully closed when the eyelid reflex is triggered.

Detailed legal assessments and/or expert opinions, if already available, can be made available to veterinary offices for official use on request.

10. Relevant jurisdiction

1. Germany: Not on the Chihuahua, but on brachycephaly in the French Bulldog: VG Stade, decision of 07.07. 2022, 10 B 481/22 and OVG Lüneburg, decision of 25.10.2022, 11 ME 221722
2. Austria: Not known.
3. Switzerland: Not known.
4. Netherlands: Amsterdam Civil Court, judgment of June 4, 2025, prohibiting the issuing of pedigrees for brachycephalic breeds. The judgment explicitly mentions the Chihuahua as one of the breeds that will no longer receive a pedigree if the parents do not meet the Dutch criteria (see also https://qualzucht-datenbank.eu/wp-content/uploads/2025/06/Urteil-brachycephale-Hunde-DE-Juni-2025.pdf ).
5. Sweden: Not known.
6. Norway: Not to the Chihuahua but to the Chiari-like malformation: The Dom Høyesterett as the highest court of appeal has determined on 10.10.2023 that the Cavalier King Charles Spaniel is to be classified as torture breeding due to the large number of serious diseases – due to the Chiari-like malformation (CM) and syringomyelia (SM) alone (HR-2023-1901-A AZ 23-004643SIV-HRET).

11. Order example available?

No.

Examples of orders are only made available to veterinary offices for official use on request.

12. Grants and Funding

13.  Bibliography/ References/ Links

At this point, only a selection of sources on the defects described above and, where applicable, general literature on breeding-related defects in dogs is provided. More extensive literature lists on the scientific background will be sent exclusively to veterinary offices upon request.

AGRIA Pet Insurance Sweden. (2022). Chihuahua Shorthaired Breed Profiles Veterinary Care 2016-2021.

AGRIA Pet Insurance Sweden. (2022). Chihuahua Longhaired Breed Profiles Veterinary Care 2016-2021.

AGRIA Pet Insurance Sweden. (2022). Chihuahua Shorthaired Breed Profiles Life 2016-2021.

AGRIA Pet Insurance Sweden. (2022). Chihuahua Longhaired Breed Profiles Life 2016-2021.

Bundesamt für Lebensmittelsicherheit. (2015). Verordnung des BLV über den Tierschutz beim Züchten. https://www.fedlex.admin.ch/eli/cc/2014/747/de

Bundesministerium für Ernährung und Landwirtschaft (BMEL). (2005). Gutachten zur Auslegung von Paragraf 11b des Tierschutzgesetzes (Qualzuchtgutachten). https://www.bmel.de/SharedDocs/Downloads/DE/_Tiere/Tierschutz/Gutachten-Leitlinien/Qualzucht.html

Dier&Recht. (2019). Kleinste Hunde-die kleinsten Hunde haben die größten Probleme. Dier&Recht. https://www.dierenrecht.nl/sites/default/files/2020-05/rapport-miniatuurhondjes.pdf

Fleming, J. M., Creevy, K. E., & Promislow, D. E. L. (2011). Mortality in North American Dogs from 1984 to 2004: An Investigation into Age‐, Size‐, and Breed‐Related Causes of Death. Journal of Veterinary Internal Medicine, 25(2), 187–198. https://doi.org/10.1111/j.1939-1676.2011.0695.x

Gelatt, K. N., & MacKay, E. O. (2005). Prevalence of primary breed‐related cataracts in the dog in North America. Veterinary Ophthalmology, 8(2), 101–111. https://doi.org/10.1111/j.1463-5224.2005.00352.x

Geiger, M., Schoenebeck, J. J., Schneider, R. A., Schmidt, M. J., Fischer, M. S., & Sánchez-Villagra, M. R. (2021). Exceptional Changes in Skeletal Anatomy under Domestication: The Case of Brachycephaly. Integrative Organismal Biology (Oxford, England), 3(1), obab023. https://doi.org/10.1093/iob/obab023

Genetics Committee of the American College of Veterinary Ophthalmologists, (ACVO). (2023). ACVO 2023 The Blue Book—Ocular disorders presumed to be inherited in purebreed dogs- Chihuahua (15th Edition). https://ofa.org/wp-content/uploads/2024/05/ACVO-Blue-Book-2023.pdf

Hale, F. A. (2021). Dental and Oral Health for the Brachycephalic Companion Animal . In Health and Welfare of Brachycephalic (Flat-faced) Companion Animals (1., S. 235–250). Taylor and Francis Group. https://www.taylorfrancis.com/chapters/edit/10.1201/9780429263231-14/dental-oral-health-brachycephalic-companion-animal-fraser-hale

Hirt, A., Maisack, C., Moritz, J., & Felde, B. (2023). Tierschutzgesetz: Mit TierSchHundeV, TierSchNutztV, TierSchVersV, TierSchTrV, EU-Tiertransport-VO, TierSchlV, EU-Tierschlacht-VO, TierErzHaVerbG: Kommentar (4. Auflage). Verlag Franz Vahlen.

Hobi, S., Barrs, V. R., & Bęczkowski, P. M. (2023). Dermatological Problems of Brachycephalic Dogs. Animals, 13(12), 2016. https://doi.org/10.3390/ani13122016

Kiviranta, A. ‐M., Rusbridge, C., Laitinen‐Vapaavuori, O., Hielm‐Björkman, A., Lappalainen, A. K., Knowler, S. P., & Jokinen, T. S. (2017). Syringomyelia and Craniocervical Junction Abnormalities in Chihuahuas. Journal of Veterinary Internal Medicine, 31(6), 1771–1781. https://doi.org/10.1111/jvim.14826

Lorz, A., & Metzger, E. (Hrsg.). (2019). Tierschutzgesetz: Mit Allgemeiner Verwaltungsvorschrift, Art. 20a GG sowie zugehörigen Gesetzen, Rechtsverordnungen und Rechtsakten der Europäischen Union: Kommentar (7. Auflage). C.H. Beck.

Mattin, M. J., Boswood, A., Church, D. B., López‐Alvarez, J., McGreevy, P. D., O’Neill, D. G., Thomson, P. C., & Brodbelt, D. C. (2015). Prevalence of and Risk Factors for Degenerative Mitral Valve Disease in Dogs Attending Primary‐care Veterinary Practices in England. Journal of Veterinary Internal Medicine, 29(3), 847–854. https://doi.org/10.1111/jvim.12591

Mattin, M. J., Boswood, A., Church, D. B., McGreevy, P. D., O’Neill, D. G., Thomson, P. C., & Brodbelt, D. C. (2015). Degenerative mitral valve disease: Survival of dogs attending primary-care practice in England. Preventive Veterinary Medicine, 122, 436–442. https://doi.org/10.1016/j.prevetmed.2015.05.007

Meola, S. D. (2013). Brachycephalic Airway Syndrome. Topics in Companion Animal Medicine, 28(3), 91–96. https://doi.org/10.1053/j.tcam.2013.06.004

Niederländische Grundsatzregelung für brachycephale Rassen (2023). https://zoek.officielebekendmakingen.nl/staatscourant/stcrt-2023-23619.pdf

Niederländischer Staatssekretär für Wirtschaft, Landwirtschaft und Innovation vom 19. Oktober 2012, Nr. 291872, Direktion für Gesetzgebung und Rechtsfragen. (2024). Niederländisches Tierhalter-Dekret. Tierhalter Dekret. https://wetten.overheid.nl/BWBR0035217/2024-07-01/#Hoofdstuk3_Paragraaf1_Artikel3.4

Nilsson, K., Zanders, S., & Malm, S. (2018). Heritability of patellar luxation in the Chihuahua and Bichon Frise breeds of dogs and effectiveness of a Swedish screening programme. The Veterinary Journal, 234, 136–141. https://doi.org/10.1016/j.tvjl.2018.01.010

O’Neill, D. G., Church, D. B., McGreevy, P. D., Thomson, P. C., & Brodbelt, D. C. (2013). Longevity and mortality of owned dogs in England. The Veterinary Journal, 198(3), 638–643. https://doi.org/10.1016/j.tvjl.2013.09.020

O’Neill, D. G., Lee, M. M., Brodbelt, D. C., Church, D. B., & Sanchez, R. F. (2017). Corneal ulcerative disease in dogs under primary veterinary care in England: Epidemiology and clinical management. Canine Genetics and Epidemiology, 4(1), 5. https://doi.org/10.1186/s40575-017-0045-5

O’Neill, D. G., Packer, R. M. A., Lobb, M., Church, D. B., Brodbelt, D. C., & Pegram, C. (2020). Demography and commonly recorded clinical conditions of Chihuahuas under primary veterinary care in the UK in 2016. BMC Veterinary Research, 16(1), 42. https://doi.org/10.1186/s12917-020-2258-1

O’Neill, D. G., Pegram, C., Crocker, P., Brodbelt, D. C., Church, D. B., & Packer, R. M. A. (2020). Unravelling the health status of brachycephalic dogs in the UK using multivariable analysis. Scientific Reports, 10(1), 17251. https://doi.org/10.1038/s41598-020-73088-y

Orthopedic Foundation for Animals (OFA). (2024). Chihuahua Breed Summary Report 2024. OFA. https://ofa.org/chic-programs/browse-by-breed/?breed=CH

Orthopedic Foundation for Animals (OFA). (o. J.). Patellar Luxation. OFA. Abgerufen 17. April 2024, von https://ofa.org/diseases/patellar-luxation/

Park, S. A., Yi, N. Y., Jeong, M. B., Kim, W. T., Kim, S. E., Chae, J. M., & Seo, K. M. (2009). Clinical manifestations of cataracts in small breed dogs. Veterinary Ophthalmology, 12(4), 205–210. https://doi.org/10.1111/j.1463-5224.2009.00697.x

Ruotanen, P. (2020). Estimation of heritability of patellar luxation in four dog breeds in Finnland. https://helda.helsinki.fi/server/api/core/bitstreams/2d37e512-38c1-4738-8075-bbf8f3aa0a54/content

Rusbridge, C., Stringer, F., & Knowler, S. P. (2018). Clinical Application of Diagnostic Imaging of Chiari-Like Malformation and Syringomyelia. Frontiers in Veterinary Science, 5, 280. https://doi.org/10.3389/fvets.2018.00280

Rusbridge, C. (2020). New considerations about Chiari‐like malformation, syringomyelia and their management. In Practice, 42(5), 252–267. https://doi.org/10.1136/inp.m1869

Sanchis‐Mora, S., Pelligand, L., Thomas, C. L., Volk, H. A., Abeyesinghe, S. M., Brodbelt, D. C., Church, D. B., Thomson, P. C., McGreevy, P. D., & O’Neill, D. G. (2016). Dogs attending primary‐care practice in England with clinical signs suggestive of Chiari‐like malformation/syringomyelia. Veterinary Record, 179(17), 436–436. https://doi.org/10.1136/vr.103651

Schweizerischer Bundesrat. (2024). Tierschutzverordnung (TSchV) Schweiz. FedLex. https://www.fedlex.admin.ch/eli/cc/2008/416/de

Teng, K. T., Brodbelt, D. C., Pegram, C., Church, D. B., & O’Neill, D. G. (2022). Life tables of annual life expectancy and mortality for companion dogs in the United Kingdom. Scientific Reports, 12(1), 6415. https://doi.org/10.1038/s41598-022-10341-6

Universität Utrecht. (2016). PETscan Entwicklung und Einführung eines quantitativen Messsystems für Gesundheit und Wohlbefinden von Haustieren-Erbkrankheiten und schädliche Rassemerkmale bei 38 Hunderassen und 2 Katzenrassen in den Niederlanden. Fakultät für Tierheilkunde von Heimtieren.
https://www.uu.nl/sites/default/files/eindrapportage_ministerie_ez_final_24022017.pdf