The nervous, endocrine and immune systems are responsible for regulating, coordinating and protecting the body. Together, these systems enable an assistance animal to perceive and respond to its environment, maintain internal physiological balance, recover from illness and injury, and perform the complex cognitive and behavioural tasks required during assistance work.

Unlike the musculoskeletal or cardiovascular systems, which are often associated with physical performance, these systems influence almost every aspect of an animal’s health. They regulate movement, sensation, learning, memory, behaviour, hormone production, metabolism, stress responses and disease resistance. Dysfunction within any of these systems may have profound effects on an assistance animal’s physical health, emotional wellbeing and capacity to safely perform its role.

For occupational therapists, understanding these body systems is particularly important because many neurological, endocrine and immune disorders initially present as subtle changes in behaviour, cognition, mobility or performance. Recognising these changes and facilitating timely veterinary assessment supports both animal welfare and the safety of the assistance animal partnership.

The Nervous System

The nervous system coordinates communication throughout the body, allowing animals to perceive their environment, process information and respond appropriately. It is responsible for movement, sensation, learning, memory, emotional regulation and the coordination of complex behaviours.

The nervous system is broadly divided into the central nervous system and the peripheral nervous system. The central nervous system consists of the brain and spinal cord, which receive, interpret and integrate information from throughout the body. The peripheral nervous system comprises the network of nerves that carry sensory information to the brain and spinal cord while transmitting motor signals to muscles and organs.

Sensory organs, including the eyes, ears, nose and skin, continually collect information about the surrounding environment. This information allows assistance animals to navigate safely, identify hazards, respond to cues, perform trained tasks and adapt to changing environments.

Efficient neurological function is fundamental to assistance work. Every trained behaviour, from responding to a handler’s verbal cue to retrieving medication or interrupting repetitive behaviours, relies on accurate communication between the brain, nerves and muscles.

Common Neurological Conditions

Neurological disease may affect movement, coordination, sensation, cognition or behaviour. The severity of clinical signs varies considerably depending on the location and extent of the underlying condition.

Epilepsy is one of the most commonly diagnosed neurological disorders in dogs. Animals experience recurrent seizures resulting from abnormal electrical activity within the brain. Although many dogs with well-controlled epilepsy live good-quality lives, recurrent or unpredictable seizures are generally incompatible with active assistance work due to the potential risks to both the handler and the animal.

Intervertebral disc disease, discussed previously in relation to the musculoskeletal system, also has significant neurological consequences when damaged discs compress the spinal cord. Depending on the severity of compression, affected animals may experience pain, weakness, incoordination or paralysis.

Degenerative neurological diseases, inflammatory disorders, brain tumours and traumatic injuries may also impair neurological function. In older animals, cognitive decline may gradually affect learning, memory, orientation and behavioural responses.

Neurological disorders often require advanced diagnostic investigations and ongoing veterinary management. Occupational therapists should recognise that sudden weakness, altered coordination, tremors, seizures, changes in behaviour or unexplained sensory deficits require prompt veterinary assessment.

The Endocrine System

The endocrine system consists of glands that produce hormones, which act as chemical messengers regulating numerous physiological processes throughout the body. Hormones influence growth, metabolism, reproduction, stress responses, blood glucose regulation and fluid balance.

Major endocrine glands include the pituitary gland, thyroid gland, adrenal glands, pancreas and reproductive organs. Unlike the nervous system, which communicates rapidly through electrical impulses, the endocrine system generally produces slower but longer-lasting effects through hormone release into the bloodstream.

Maintaining hormonal balance is essential for normal health. Even relatively small hormonal disturbances may affect behaviour, body weight, appetite, energy levels, immune function and physical performance.

Common Endocrine Conditions

Several endocrine disorders are relatively common in companion animals and may significantly affect assistance animal welfare and working capacity.

Hypothyroidism is one of the most frequently diagnosed endocrine disorders in dogs. Reduced production of thyroid hormones slows metabolism, often resulting in lethargy, weight gain, exercise intolerance, poor coat quality and reduced enthusiasm for work. Because these signs often develop gradually, they may initially be mistaken for normal ageing.

Diabetes mellitus occurs when the body cannot adequately regulate blood glucose concentrations. Affected animals commonly experience increased thirst, increased urination, weight loss despite a good appetite and reduced energy levels. Successful management typically requires lifelong insulin therapy, dietary management and regular veterinary monitoring.

Hyperadrenocorticism (Cushing’s disease) results from excessive cortisol production. Clinical signs may include increased thirst and urination, increased appetite, muscle weakness, abdominal enlargement, thinning skin and reduced exercise tolerance.

Conversely, hypoadrenocorticism (Addison’s disease) involves inadequate production of adrenal hormones. Animals may present with intermittent lethargy, vomiting, diarrhoea, weakness or collapse. Although potentially life-threatening if untreated, most animals respond well to appropriate lifelong treatment.

The Immune System

The immune system protects the body against infectious organisms, abnormal cells and other potentially harmful substances. It consists of a complex network of specialised cells, tissues, organs and signalling molecules that work together to identify and eliminate pathogens while maintaining tolerance to the body’s own tissues.

The immune system provides both innate and adaptive immunity. Innate immunity offers rapid, non-specific protection against invading organisms, while adaptive immunity develops more targeted responses following exposure to specific pathogens or vaccination.

A healthy immune system enables assistance animals to recover from infection, respond appropriately to vaccination and resist many common diseases encountered during daily life.

Common Immune-Mediated Conditions

Occasionally, the immune system functions abnormally and begins attacking the body’s own tissues. These immune-mediated diseases may affect almost any organ system and often require lifelong veterinary management.

Immune-mediated polyarthritis causes inflammation within multiple joints, resulting in pain, stiffness and reduced mobility. Immune-mediated haemolytic anaemia involves destruction of red blood cells, leading to weakness, lethargy and potentially life-threatening anaemia.

Allergic disease also involves inappropriate immune responses to normally harmless substances. Environmental allergies, food allergies and flea allergy dermatitis are common examples and may result in chronic skin disease, itching or recurrent ear infections.

Animals receiving medications that suppress the immune system require careful monitoring because they may become more susceptible to infection.

Behavioural Changes as Indicators of Medical Disease

Changes in behaviour are sometimes attributed to training difficulties or temperament when, in fact, they reflect underlying medical illness. Neurological disease, endocrine disorders, chronic pain and systemic illness may all alter an animal’s behaviour long before obvious physical signs develop.

An assistance animal that becomes unusually reluctant to work, appears confused, demonstrates reduced responsiveness to familiar cues or shows unexpected changes in temperament should always receive a thorough veterinary assessment before behavioural explanations are considered.

Similarly, increased anxiety, altered sleep patterns, changes in appetite or reduced social engagement may reflect underlying medical disease rather than behavioural regression.

For occupational therapists, maintaining an awareness of the close relationship between physical health and behaviour is essential when evaluating changes in an assistance animal’s occupational performance.

Supporting Neurological, Endocrine and Immune Health

Maintaining these body systems requires a combination of preventative healthcare, appropriate nutrition, regular exercise, vaccination, parasite prevention and routine veterinary monitoring. Early recognition of subtle behavioural or physiological changes often allows intervention before disease progresses to more advanced stages.

Regular health assessments become increasingly important as assistance animals age, as many neurological and endocrine disorders develop gradually and may initially produce only mild clinical signs. Ongoing collaboration between handlers, veterinarians and allied animal health professionals supports early diagnosis and optimises long-term health outcomes.

Occupational Therapy Considerations

The nervous, endocrine and immune systems underpin an assistance animal’s ability to learn, respond to cues, regulate behaviour, maintain energy levels and remain physically healthy throughout its working life. Dysfunction within these systems may significantly affect an animal’s occupational performance, even when outward physical signs are subtle.

Occupational therapists should remain alert to changes in cognition, behaviour, coordination, endurance and responsiveness during therapy sessions and community activities. Medical conditions affecting these systems may present initially as reduced concentration, altered task performance, increased fatigue or behavioural changes rather than obvious illness.

Recognising these early indicators and facilitating prompt veterinary referral supports timely diagnosis, protects animal welfare and promotes the continued safety and effectiveness of the assistance animal partnership. Through collaborative practice with veterinarians and other professionals, occupational therapists contribute to holistic, evidence-informed care that recognises the interconnected relationship between physical health, behaviour and occupational participation.