Selecting an assistance animal involves more than choosing an animal with an appropriate temperament and willingness to work. The animal’s physical structure, proportions and body shape also influence its ability to safely perform assistance tasks throughout its working life.

Conformation refers to the overall physical shape and structure of an animal. It includes characteristics such as skull shape, body size, limb proportions, body length and chest shape. These characteristics influence movement, endurance, balance, breathing, heat regulation and susceptibility to inherited health conditions. While no single conformational type determines whether an animal will succeed as an assistance animal, understanding these characteristics helps explain why some animals may be better suited to particular working roles than others.

It is important to recognise that most breeds possess multiple conformational characteristics. For example, a Pembroke Welsh Corgi is mesocephalic, chondrodystrophic, long-backed and double-coated, while a Standard Poodle is mesocephalic, deep-chested and curly-coated. These characteristics interact to influence the animal’s overall function, health and welfare.

The following sections introduce the major conformational categories encountered in dogs and discuss how these characteristics may influence assistance animal selection.

Table 5.1. Common conformational categories, associated health considerations and general suitability for assistance work.

Important: These categories describe physical characteristics rather than determining suitability for assistance work. Most breeds possess several conformational characteristics simultaneously, and no single trait automatically qualifies or excludes an animal from assistance work. Every prospective assistance animal should be assessed individually, considering its health, temperament, behaviour, functional capacity and welfare alongside the physical requirements of its intended role.

Skull Shape

One of the most recognisable aspects of canine conformation is skull shape. Skull conformation influences much more than appearance; it affects breathing, thermoregulation, vision, dentition, scenting ability and exercise tolerance. Veterinary medicine generally classifies canine skulls into three broad categories: dolichocephalic (long-headed), mesocephalic (moderate-headed) and brachycephalic (short-headed).

These categories exist along a continuum rather than as rigid classifications, and many breeds display characteristics between the traditional groups. Understanding these skull types helps explain why certain breeds are predisposed to specific health conditions and why some are more commonly selected for assistance work.

Dolichocephalic Dogs

Dolichocephalic dogs possess long, narrow skulls and elongated muzzles. Examples include Greyhounds, Whippets, Salukis, Borzois and Rough Collies.

Many dolichocephalic breeds were originally developed for hunting or sight-based pursuits requiring speed, endurance and keen vision. Their elongated skulls generally allow efficient airflow and thermoregulation, making respiratory compromise uncommon compared with brachycephalic breeds.

However, some breeds are predisposed to inherited eye disease, dental disease, gastric dilatation-volvulus (GDV) and increased sensitivity to certain anaesthetic agents. Sighthounds also tend to have thinner skin and lower body fat, increasing their susceptibility to traumatic injury.

Many dolichocephalic breeds can make excellent assistance animals provided they possess the appropriate temperament, health and behavioural characteristics.

Mesocephalic Dogs

Mesocephalic dogs possess a balanced skull shape with moderate muzzle length and are generally considered to have the fewest conformational compromises affecting the head and upper airway.

Many of the breeds most frequently selected as assistance dogs belong to this group, including Labrador Retrievers, Golden Retrievers, Standard Poodles, Border Collies, Australian Kelpies, German Shepherd Dogs and English Springer Spaniels.

The popularity of the so-called “Fab Four”—Labrador Retrievers, Golden Retrievers, Standard Poodles and Border Collies—reflects the combination of trainability, temperament, physical function and adaptability that these breeds often demonstrate when responsibly bred and appropriately assessed.

Although mesocephalic breeds generally have fewer skull-related health concerns than brachycephalic breeds, they remain susceptible to breed-specific inherited conditions such as hip and elbow dysplasia, inherited eye disease, epilepsy and other genetic disorders. Appropriate health screening remains essential regardless of skull shape.

Brachycephalic Dogs

Brachycephalic dogs possess shortened skulls and flattened faces resulting from selective breeding. Common examples include French Bulldogs, English Bulldogs, Pugs, Boston Terriers, Shih Tzus, Pekingese and Boxers.

While many brachycephalic dogs are affectionate companion animals, increasing evidence has highlighted significant welfare concerns associated with extreme brachycephalic conformation. One of the most important is Brachycephalic Obstructive Airway Syndrome (BOAS), which results from narrowing of the upper airway due to anatomical abnormalities such as stenotic nares, elongated soft palate and narrowed airways.

Affected dogs may experience chronic breathing difficulties, noisy respiration, exercise intolerance and difficulty regulating body temperature. Because dogs primarily cool themselves through panting, impaired airflow significantly increases the risk of heat stress and heat stroke.

Additional health concerns include dental overcrowding, ocular disease, skin fold dermatitis, sleep-disordered breathing and increased anaesthetic risk.

For these reasons, brachycephalic breeds are less commonly selected for assistance work. However, skull shape alone should not automatically exclude an individual dog. Selection should instead focus on whether the individual demonstrates normal respiratory function, good exercise tolerance and the ability to perform the required tasks comfortably without compromising welfare.

Body Size

Body size influences the types of assistance tasks an animal can safely perform, the environments in which it can comfortably work and practical considerations such as transport, housing and handling.

Dogs are commonly grouped into toy, small, medium, large and giant size categories. No single size is inherently superior for assistance work. Instead, the most appropriate size depends on the handler’s disability-related needs and the tasks the animal will perform.

Toy and small breeds may be well suited to medical alert, psychiatric assistance and hearing assistance roles where physical strength is not required. Medium-sized breeds, including the Fab Four, are the most commonly selected because they offer an excellent balance of strength, agility, endurance and adaptability. Large and giant breeds may be appropriate for some specialised roles requiring greater height or strength, although their shorter average lifespan and increased prevalence of orthopaedic disease should be considered during selection.

The most appropriate body size is therefore one that safely meets the functional needs of the handler while supporting the long-term health and welfare of the animal.

Limb Proportions

Limb proportions refer to the relative length and structure of an animal’s forelimbs and hindlimbs. These proportions influence stride length, efficiency of movement, jumping ability, endurance and the distribution of forces across the joints and spine. Different limb proportions evolved to perform different types of work, with no single body type being universally superior. Instead, suitability depends on the physical requirements of the intended assistance role.

Many assistance dogs possess limbs that are proportionate to their body size, allowing efficient movement over long periods while minimising stress on the musculoskeletal system. However, some breeds have been selectively bred for markedly shortened limbs or disproportionate body proportions, resulting in unique functional advantages but also increased susceptibility to certain orthopaedic conditions.

Understanding these differences helps occupational therapists appreciate why limb structure is considered alongside temperament, behaviour and health when selecting prospective assistance animals.

Chondrodystrophy and Achondroplasia

One of the best-known examples of altered limb proportions is chondrodystrophy, a genetic condition characterised by shortened limbs resulting from abnormal cartilage development. The term is sometimes used interchangeably with achondroplasia, although chondrodystrophy more accurately describes the inherited form of disproportionate dwarfism seen in many dog breeds.

Examples include:

• Dachshund
• Pembroke Welsh Corgi
• Cardigan Welsh Corgi
• Basset Hound
• Skye Terrier
• Glen of Imaal Terrier

Historically, these breeds were developed for specialised working roles requiring short legs and elongated bodies. Dachshunds, for example, were bred to pursue badgers and other burrowing animals underground, while Corgis were developed to herd cattle by working close to the ground and avoiding kicks from livestock.

Although these conformational characteristics were advantageous for their original purpose, they also increase the risk of several inherited musculoskeletal conditions.

Intervertebral Disc Disease (IVDD)

The condition most commonly associated with chondrodystrophic breeds is intervertebral disc disease (IVDD).

Intervertebral discs act as cushions between the vertebrae of the spine. In chondrodystrophic dogs, these discs frequently undergo premature degeneration, becoming less flexible and more prone to rupture. When disc material protrudes into the spinal canal, it may compress the spinal cord, resulting in pain, weakness or paralysis.

Clinical signs vary depending on the severity and location of the injury and may include:

• reluctance to move
• back or neck pain
• altered gait
• weakness
• dragging of the limbs
• urinary or faecal incontinence
• paralysis.

Many affected dogs recover with appropriate veterinary treatment, while others require surgical intervention or lifelong management.

Because assistance animals are expected to accompany their handlers daily and perform consistent physical tasks, IVDD represents an important welfare consideration during animal selection.

Other Orthopaedic Considerations

In addition to IVDD, some chondrodystrophic breeds have an increased prevalence of:

• elbow incongruity
• angular limb deformities
• premature osteoarthritis
• obesity
• reduced jumping ability
• altered biomechanics.

These conditions may not prevent an individual from living a healthy and fulfilling life as a companion animal but may reduce comfort during prolonged working activities or physically demanding assistance tasks.

Implications for Assistance Work

Short-legged breeds are capable of learning complex behaviours and may possess excellent temperaments for assistance work. Their intelligence, trainability and close bond with people should not be underestimated.

However, their physical structure may limit the types of tasks they can safely perform.

For example, repeated retrieval from the floor, negotiating large flights of stairs, jumping into vehicles or accompanying handlers over long distances may place greater biomechanical stress on the spine and limbs than in proportionately built dogs.

Conversely, many chondrodystrophic breeds may be well suited to less physically demanding roles, such as:

• medical alert
• psychiatric assistance
• hearing assistance
• task work performed primarily within the home.

Selection should therefore focus on matching the physical capabilities of the individual animal with the functional requirements of the intended assistance role.

Selecting for Function Rather Than Appearance

Historically, some breeds have become increasingly exaggerated in appearance through selective breeding. While these exaggerated characteristics may satisfy breed standards or aesthetic preferences, they do not necessarily improve health or function.

Modern assistance animal programs increasingly emphasise functional conformation rather than exaggerated physical traits. The objective is to select animals capable of moving comfortably, performing their duties without pain and maintaining good quality of life throughout their working careers.

Consequently, chondrodystrophic breeds should not be selected or excluded solely because of their appearance. Instead, decisions should be based on comprehensive assessment of the individual dog’s health, movement, temperament, intended tasks and long-term welfare.

Occupational Therapy Considerations

Occupational therapists should recognise that limb proportions influence an animal’s physical capabilities but do not determine its intelligence, trainability or suitability for assistance work. When discussing prospective assistance animals with clients, occupational therapists should consider how the physical demands of the intended assistance role align with the animal’s body structure and encourage referral to appropriately qualified assistance animal professionals and veterinarians where additional assessment is required. Selection should prioritise long-term function, safety and welfare rather than appearance alone.

Body Length

Body length refers to the relationship between the length of the spine and the height of the limbs. Dogs display considerable variation in body proportions, ranging from square-bodied breeds with relatively equal height and length to long-bodied breeds with elongated spines.

These differences developed through selective breeding to enable particular working roles. For example, Dachshunds and Basset Hounds were bred with elongated bodies to enable them to enter underground burrows, while Border Collies and Australian Kelpies possess more balanced body proportions that support agility, endurance and rapid changes in direction during herding work.

Body length alone does not determine whether a dog is suitable for assistance work. However, it may influence biomechanics, movement efficiency and susceptibility to certain musculoskeletal disorders.

Long-Backed Dogs

Long-backed breeds possess an elongated spine relative to their height. Examples include:

• Dachshund
• Welsh Corgi
• Basset Hound
• Swedish Vallhund

The increased length of the vertebral column creates greater mechanical forces across the spine during movement. In breeds already genetically predisposed to intervertebral disc disease (IVDD), this increases the likelihood that degenerative disc disease may develop during the dog’s lifetime.

Activities involving repeated jumping, climbing, twisting or sudden changes in direction may place additional strain on the spine. Likewise, excess body weight substantially increases loading on both the spine and joints, making maintenance of an ideal body condition particularly important.

Long-backed dogs are not inherently unsuitable for assistance work. However, the physical requirements of the intended role should be carefully considered to ensure they can perform required tasks comfortably throughout their working life.

Balanced Body Proportions

Many of the breeds most commonly selected for assistance work possess body proportions that are close to square or only slightly longer than they are tall.

Examples include:

• Labrador Retriever
• Golden Retriever
• Border Collie
• Standard Poodle
• Australian Kelpie

Balanced body proportions generally promote efficient weight distribution, coordinated movement and reduced mechanical stress across the spine. These characteristics may contribute to improved endurance during prolonged public access work and repeated daily activities.

Balanced proportions also allow greater versatility across a wide range of assistance tasks, including retrieving objects, navigating varied environments and accompanying handlers throughout extended periods of community participation.

Extremely Short or Compact Bodies

Some breeds possess compact body proportions with relatively short backs and broad bodies. While these conformations may provide stability, they may also reduce stride length, agility and exercise efficiency depending on the individual breed.

As with all conformational traits, suitability depends on the individual dog’s overall health, fitness and the specific requirements of the assistance role rather than body shape alone.

Chest Shape

Chest conformation influences breathing capacity, endurance, movement and, in some breeds, susceptibility to serious medical conditions.

Dogs demonstrate considerable variation in chest shape, ranging from deep, narrow chests to broader, barrel-shaped thoraxes. These differences developed to support different working functions and athletic abilities.

Understanding chest conformation helps explain why some breeds possess excellent endurance while others may be predisposed to conditions requiring additional management throughout their working lives.

Deep-Chested Dogs

Deep-chested dogs possess a thorax that extends well towards the elbows, creating increased space for the heart and lungs. Examples include:

• Standard Poodle
• Great Dane
• Dobermann
• Weimaraner
• German Shepherd Dog
• Irish Setter

This conformation often supports excellent cardiovascular and respiratory capacity, allowing sustained exercise and endurance. Consequently, many deep-chested breeds perform exceptionally well in physically demanding working roles.

However, deep-chested conformation is also associated with an increased risk of Gastric Dilatation-Volvulus (GDV), commonly known as bloat.

GDV occurs when the stomach fills with gas and rotates, cutting off its own blood supply and compromising circulation to other organs. It is a rapidly progressive veterinary emergency requiring immediate surgical treatment.

Although the precise cause remains uncertain, recognised risk factors include:

• deep, narrow chest conformation
• increasing age
• rapid food consumption
• vigorous exercise immediately before or after meals
• family history
• large or giant breed size.

Prospective handlers of deep-chested assistance dogs should receive education regarding the clinical signs of GDV and understand that immediate veterinary attention is essential should these signs occur.

Broad or Barrel-Chested Dogs

Breeds such as Bulldogs, Pugs and some Mastiffs possess broader, barrel-shaped chests.

Although this conformation is not generally associated with GDV to the same extent as deep-chested breeds, overall respiratory function and endurance may be influenced by other conformational characteristics, particularly in brachycephalic breeds.

Chest shape should therefore always be considered together with overall body structure rather than in isolation.

Narrow-Chested Athletic Dogs

Many athletic breeds, including Greyhounds and Whippets, possess relatively narrow but deep chests that contribute to efficient movement and speed.

This streamlined conformation reduces body weight while maintaining adequate thoracic capacity for cardiovascular performance. However, it may also contribute to their predisposition to GDV and increase susceptibility to traumatic injury because of reduced muscle and fat coverage over the ribs.

These characteristics do not preclude assistance work but should be considered alongside the individual’s overall health and intended role.

Matching Chest Conformation to Function

Chest shape should not be viewed as either desirable or undesirable in isolation. Rather, it forms one component of the animal’s overall conformation and should be considered together with temperament, behaviour, health and the physical requirements of the intended assistance role.

For example, a deep-chested Standard Poodle may possess outstanding endurance and trainability, making it an excellent assistance dog despite the increased risk of GDV. Similarly, a Labrador Retriever’s moderately broad chest contributes to its strength and versatility across many assistance roles.

The objective is not to identify a single “ideal” chest shape but to understand how different conformational characteristics influence function, welfare and long-term health.

Occupational Therapy Considerations

Occupational therapists are not expected to assess conformation or determine whether an animal is physically suitable for assistance work. However, understanding how limb proportions, body length and chest shape influence movement, endurance and long-term welfare enables occupational therapists to participate more effectively in interdisciplinary discussions regarding animal selection. Appreciating these principles also supports realistic conversations with clients about why certain breeds or body types may be better suited to particular assistance roles and reinforces the importance of selecting animals based on function, health and welfare rather than appearance alone.