Canine Pelvic Limb Musculature: Actions and Innervation

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-08-11

Key Takeaways

• The canine pelvic limb musculature is functionally organized around the coxofemoral joint, with distinct nerve territories (femoral, obturator, sciatic) dictating predictable clinical signs of dysfunction. Femoral nerve lesions result in stifle extension deficits and quadriceps atrophy, while sciatic nerve lesions cause deficits in hock and stifle flexion, leading to a plantigrade stance and distal limb knuckling.
• Gait observation and palpation are foundational for neuromuscular assessment, with specific gait abnormalities (e.g., shortened stride, plantigrade stance, crouched stance) localizing deficits to muscle groups and their respective nerves. Palpation assesses muscle bulk, with atrophy of the biceps femoris or quadriceps indicating sciatic or femoral nerve dysfunction, respectively.
• Manual muscle testing and reflex assessment provide further localization; diminished patellar reflexes suggest femoral nerve compromise, while absent withdrawal reflexes below the stifle point to sciatic nerve injury. Stretch reflexes, such as the cranial tibial and gastrocnemius reflexes, can further differentiate peroneal from tibial nerve involvement.
• Electrodiagnostic testing, including electromyography (EMG) and nerve conduction studies, is crucial for confirming denervation and characterizing nerve injury (axonal loss vs. demyelination), especially when physical examination findings are equivocal or to establish a baseline for serial assessment. Denervated muscle exhibits fibrillation potentials and prolonged insertional activity on EMG.
• Thermographic imaging can serve as an adjunctive tool to detect superficial muscle temperature changes, reflecting functional activation patterns, but requires standardized region-of-interest selection and does not replace electrodiagnostics for nerve injury confirmation. Significant temperature increases in the biceps femoris and gracilis after exercise, as measured by linear region-of-interest analysis, indicate muscle activation.

This reference article details the major muscle groups of the canine pelvic limb, their osseous attachments, actions across the coxofemoral, stifle, and tarsal joints, and their segmental innervation. It is written for veterinary students and practitioners who require a functional understanding of hindlimb myology for locomotor examination, neurologic localization, and surgical approaches. The content is organized by muscle group, with emphasis on the clinically relevant distinction between muscles supplied by the femoral and obturator nerves versus those supplied by the sciatic nerve and its branches.

The article assumes familiarity with basic musculoskeletal terminology and gross dissection. It does not address myopathic disease processes, congenital anomalies, or specific surgical techniques. The focus is on normal anatomy and the predictable relationships between muscle action, joint movement, and nerve supply that underpin clinical reasoning in the pelvic limb.

At a Glance

Functional Organization of the Pelvic Limb

The pelvic limb musculature is arranged in concentric groups around the coxofemoral joint, with distal muscles acting primarily on the stifle and tarsus. The hip joint is the primary site of power generation for propulsion, while the stifle and tarsus transmit and redirect that force through the limb. Understanding the biomechanical axis of the limb, from the ilium through the femoral head to the calcaneus, clarifies why certain muscle groups act synergistically and why specific nerve injuries produce predictable gait deficits.

The pelvic limb receives its motor supply from the lumbosacral plexus, formed by ventral branches of the L4 through S3 spinal nerves. The two dominant terminal nerves are the femoral nerve, which exits the pelvic canal through the iliopsoas muscle, and the sciatic nerve, which passes through the greater sciatic foramen caudal to the hip joint. The obturator nerve, a smaller but clinically significant branch, courses through the obturator foramen to supply the adductor compartment. The pudendal and caudal gluteal nerves complete the major pelvic limb innervation.

Gluteal Musculature

The gluteal group comprises the superficial, middle, and deep gluteal muscles, along with the tensor fasciae latae. The middle gluteal muscle is the largest and most powerful extensor of the hip, originating from the dorsal ilium and inserting on the greater trochanter. The deep gluteal muscle lies beneath it and acts primarily as an abductor and internal rotator of the hip. The superficial gluteal muscle, smaller and more caudally positioned, assists in hip extension and abduction.

The tensor fasciae latae originates from the tuber coxae and inserts into the fascia lata, which blends with the biceps femoris tendon distally. This muscle flexes the hip and tenses the fascia lata, contributing to lateral stability of the stifle during weight bearing. All gluteal muscles receive innervation from the cranial gluteal nerve, derived from L6 through S1 spinal segments. The tensor fasciae latae also receives a contribution from the femoral nerve in some individuals, a variation that has clinical relevance when assessing isolated femoral nerve lesions.

Medial Thigh Compartment

The medial thigh contains the adductor muscles, the gracilis, and the pectineus. The adductor magnus et brevis is the principal adductor of the hip, originating from the pelvic symphysis and inserting along the caudal femoral shaft. The gracilis is a broad, superficial muscle that spans from the pelvic symphysis to the cranial tibia, acting as both a hip adductor and a stifle flexor. The pectineus, originating from the iliopubic eminence, adducts the hip and is clinically relevant in hip dysplasia management.

All muscles of the medial compartment receive innervation from the obturator nerve, which arises from L4 through L6 spinal segments. The obturator nerve passes through the obturator foramen and divides into cranial and caudal branches. Damage to this nerve, which can occur during pelvic trauma or surgical approaches to the pelvic canal, results in loss of hip adduction and a characteriztic abduction of the limb during weight bearing.

Femoral Nerve Territory

The femoral nerve innervates the iliopsoas, the quadriceps femoris, and the sartorius. The iliopsoas, composed of the psoas major and iliacus, is the primary flexor of the hip. It originates from the ventral lumbar vertebrae and the ilium, inserting on the lesser trochanter. The quadriceps femoris, with its four heads, is the sole extensor of the stifle. The rectus femoris crosses the hip joint and therefore also flexes the hip, while the vastus lateralis, medialis, and intermedius originate from the femoral shaft.

The sartorius is a strap-like muscle that courses from the iliac crest to the medial tibia. It flexes the hip and extends the stifle, acting as a cranial stabilizer of the limb. Femoral nerve injury produces an inability to extend the stifle, with the limb carried in a flexed position during the swing phase. The patellar reflex, mediated by the femoral nerve, is diminished or absent in such cases.

Sciatic Nerve Territory

The sciatic nerve is the largest nerve in the body and supplies the hamstring group, the crural muscles, and all intrinsic muscles of the paw. The hamstring group includes the biceps femoris, semitendinosus, and semimembranosus. The biceps femoris is a massive muscle that extends the hip, flexes the stifle, and extends the tarsus through its distal tendon. The semitendinosus and semimembranosus act similarly, with the semitendinosus also contributing to internal rotation of the tibia.

The sciatic nerve divides into the common peroneal and tibial nerves at the level of the stifle. The common peroneal nerve supplies the cranial tibial, long digital extensor, and peroneus longus muscles, which flex the tarsus and extend the digits. The tibial nerve supplies the gastrocnemius, superficial digital flexor, and deep digital flexor, which extend the tarsus and flex the digits. Complete sciatic nerve injury produces a dropped tarsus, knuckling of the paw, and loss of conscious proprioception in the distal limb. The hamstring muscles are variably affected depending on the level of injury, since the proximal branches to the biceps femoris and semitendinosus arise before the main division.

Applied Assessment of Pelvic Limb Muscle Function

Gait Observation and Localization

The first step in evaluating pelvic limb musculature is systematic observation of the stance and swing phases. A shortened stride with reduced cranial advancement of the limb suggests weakness or pain in the flexor muscle groups, particularly the iliopsoas, sartorius, and cranial sartorius. A plantigrade stance, in which the hock drops and the paw flattens, indicates failure of the common calcanean tendon apparatus or dysfunction of the gastrocnemius and superficial digital flexor. A crouched stance with the stifle held in flexion points toward quadriceps femoris insufficiency, often from femoral nerve dysfunction.

Observe the dog from the side, from behind, and from the front during straight-line walking, circling, and stair negotiation. Circling in a tight arc exposes subtle weakness in the medial thigh adductors, as the dog may drift laterally or fail to cross over. Backing up requires coordinated activity of the hamstring group and the gluteals, reluctance or inability to back up is an early indicator of sciatic nerve territory dysfunction.

Palpation follows observation. Assess muscle bulk symmetrically, comparing the left and right pelvic limbs at the same landmarks. The biceps femoris forms the caudal contour of the thigh and is the most accessible muscle for bulk assessment. The semitendinosus and semimembranosus lie deep and medial to it. The quadriceps femoris is palpated cranial to the femur. Atrophy of the gluteals is best appreciated by palpating the region dorsal to the greater trochanter and comparing the prominence of the tuber sacrale and tuber ischiadicum on each side.

Manual Muscle Testing and Stretch Responses

Manual muscle testing in the dog is limited by cooperation and pain, but a graded approach provides useful information. With the dog in lateral recumbency, support the limb and assess resistance to extension and flexion of each joint. Grade resistance as normal, mildly reduced, severely reduced, or absent. Compare with the contralateral limb.

The withdrawal reflex tests the integrity of the sciatic nerve and its muscle targets. Pinch the distal phalanx of the pelvic limb digits. A normal response is flexion of the hock and stifle, mediated by the sciatic nerve, followed by flexion of the hip, mediated by the femoral nerve through the iliopsoas and sartorius. Absence of hock flexion with preserved hip flexion localizes the lesion to the sciatic nerve or its branches. The patellar reflex tests the femoral nerve and quadriceps femoris. A reduced or absent patellar reflex with intact withdrawal suggests a femoral nerve lesion, while a hyperactive reflex suggests an upper motor neuron lesion.

Stretch responses are assessed by rapid passive flexion of a joint. The myotatic stretch of the quadriceps is elicited by tapping the patellar tendon. The cranial tibial reflex, tapping the tendon of the cranial tibial muscle as it crosses the hock, tests the peroneal branch of the sciatic nerve. The gastrocnemius reflex, tapping the common calcanean tendon, tests the tibial branch.

Electrodiagnostic Confirmation

Electromyography (EMG) is indicated when physical examination suggests denervation but the distribution is unclear. Insertional activity is assessed first. Normal muscle shows brief insertional activity that ceases promptly. Denervated muscle shows prolonged insertional activity, fibrillation potentials, and positive sharp waves, typically appearing 5 to 7 days after denervation.

Nerve conduction studies complement EMG. Motor nerve conduction velocity of the tibial and peroneal nerves is measured by stimulating proximally and distally and recording from a distal muscle. Reduced conduction velocity with preserved amplitude suggests demyelination. Reduced amplitude with preserved velocity suggests axonal loss. Sensory nerve conduction is assessed in the superficial peroneal and sural nerves.

Electrodiagnostic findings must be interpreted alongside the physical examination. A dog with a complete sciatic nerve transection shows absent voluntary movement, absent withdrawal, and denervation potentials in the muscles distal to the lesion within 10 to 14 days. The cranial tibial muscle is the most reliable site for sampling in the peroneal distribution, and the gastrocnemius for the tibial distribution.

Thermographic Imaging as an Adjunctive Tool

Infrared thermography provides a non-invasive measure of superficial muscle temperature and has been evaluated as an adjunct to physical examination in canine hindlimb assessment. In a pilot study of healthy dogs, thermographic imaging of the gastrocnemius, biceps femoris, and gracilis before and after a 6-minute walk showed that the method of region of interest selection materially affects the result. Single-pixel measurements detected no significant temperature change in any muscle, while linear region of interest measurements detected significant increases in the biceps femoris and gracilis after walking. The gastrocnemius showed no significant temperature increase with either method. The study also noted higher temperatures in the right biceps femoris compared with the left, a finding that warrants caution when comparing contralateral limbs without accounting for baseline asymmetry. Thermography is therefore best used as a serial monitoring tool in an individual patient instead of as a single diagnostic test, and standardized region of interest selection is required for meaningful comparison across time points.

Muscle Table for Clinical Reference

The following table consolidates the origin, insertion, action, and nerve supply for the major pelvic limb muscles. Use it as a rapid reference during dissection review or when formulating a neuroanatomical localization.

Decision Points in Neuromuscular Localization

The distribution of clinical signs distinguishes between the major nerve territories. Femoral nerve dysfunction produces quadriceps atrophy, loss of the patellar reflex, and an inability to bear weight on the affected limb with the stifle held in flexion. Sciatic nerve dysfunction produces hock and stifle flexion deficits, knuckling of the paw, and atrophy of the caudal thigh and distal limb muscles. Obturator nerve dysfunction produces adductor weakness, best appreciated when the dog stands on a smooth surface and the limb slips laterally. The pelvic limb may abduct during weight bearing.

When the physical examination suggests a peripheral nerve lesion, the next decision is whether the lesion is proximal or distal to the muscle branches. A lesion at the lumbosacral plexus affects multiple nerves simultaneously. A lesion at the sciatic notch affects the sciatic nerve but spares the femoral and obturator territories. A lesion distal to the stifle affects only the peroneal or tibial branches. Electrodiagnostic testing refines this localization by identifying the most proximal level at which denervation is present.

Imaging is indicated when a compressive or infiltrative lesion is suspected. Survey radiographs identify pelvic fractures, hip luxation, or lumbosacral disease. Advanced imaging, where available, is required to evaluate the lumbosacral plexus and the intrapelvic course of the obturator and sciatic nerves. The choice of imaging modality depends on the suspected pathology and the equipment available. Cross-sectional imaging provides the best soft tissue detail but is not universally accessible. In settings where advanced imaging is unavailable, electrodiagnostic testing and careful serial physical examination remain the primary tools.

The evidence base for specific diagnostic thresholds in canine pelvic limb neuromuscular disease is limited. The thermographic pilot study referenced above illustrates this point: it involved 11 healthy dogs and reported variable results depending on measurement technique. Findings from such studies should inform clinical reasoning but should not be treated as normative standards. Similarly, the physiological studies of exercise hyperemia in canine hindlimb muscles, which examined adenosine and AMP release during muscle contraction, provide background on muscle blood flow regulation but do not directly inform clinical diagnosis. Clinicians should rely on the combination of gait analysis, palpation, reflex testing, and electrodiagnostics, and should document findings serially to detect progression or improvement.

Recognized Complications and Early Detection

Pelvic limb muscle dysfunction in dogs presents several recognizable failure modes. Sciatic nerve injury produces a plantigrade stance, reduced hock flexion during the swing phase, and progressive atrophy of the caudal thigh and crural muscles. Early detection relies on serial gait assessment and palpation of muscle bulk, particularly the biceps femoris and semitendinosus, which lose measurable mass within 10 to 14 days of denervation. Femoral nerve dysfunction causes quadriceps atrophy, a stiff extended stifle, and inability to bear weight on the affected limb. The patellar reflex becomes depressed or absent, and the dog may knuckle over the dorsal paw because proprioceptive deficits accompany motor loss.

Compartment syndrome, though uncommon in the pelvic limb, follows severe trauma or prolonged recumbency. The affected muscle group becomes firm, painful on passive extension, and the overlying skin may appear tense. Early detection requires serial measurement of limb circumference and repeated palpation, because pain out of proportion to the visible injury is the earliest reliable sign. Ischemic contracture of the quadriceps, a recognized complication of femoral fracture repair or prolonged tight bandaging, presents as a stiff, shortened quadriceps with a fixed extended stifle. Detection depends on recognizing reduced stifle flexion during gait and on palpating a taut, non-compliant quadriceps belly.

Thermographic imaging offers a non-invasive method for detecting superficial temperature changes in specific muscles. In a pilot study of healthy dogs, a 6-minute walk produced significant temperature increases in the biceps femoris and gracilis when assessed by linear region-of-interest analysis, but not in the gastrocnemius. The same study found no significant temperature change using single-pixel analysis, which underscores the importance of standardized image acquisition and analysis methods. Thermography detects functional activation patterns, not denervation, and should not replace electrodiagnostic testing when nerve injury is suspected.

Common Errors and Corrective Actions

Less experienced clinicians frequently misattribute pelvic limb lameness to joint disease when the primary problem is muscular. The biceps femoris and gracilis are common sites of strain, and pain on palpation may be mistaken for stifle or hip pain. The corrective action is systematic palpation of each muscle belly before joint manipulation, with the dog standing and then in lateral recumbency. A second common error is assuming that a normal patellar reflex excludes femoral nerve injury. The reflex tests the L4 to L6 spinal segments and the femoral nerve, but a partial nerve lesion may leave the reflex intact while quadriceps strength is reduced. The corrective action is to assess quadriceps muscle tone and weight-bearing capacity directly, not to rely on the reflex alone.

Students often confuse the innervation territories of the sciatic and femoral nerves because both contribute to stifle and tarsal function. The discriminating feature is that the sciatic nerve supplies the hamstring muscles and all muscles distal to the stifle, while the femoral nerve supplies the quadriceps and iliopsoas. A dog with a sciatic lesion can bear weight but has a dropped hock, whereas a dog with a femoral lesion cannot extend the stifle and collapses at the knee. Another frequent error is failing to distinguish between the superficial and deep gluteal muscles when assessing hip extension. The superficial gluteal is a powerful extensor and abductor, while the deep gluteal is primarily a stabilizer of the hip joint. Palpation of each muscle separately, with the hip in flexion and extension, clarifies which structure is painful.

Limitations of Current Evidence

The evidence base for canine pelvic limb muscle physiology rests heavily on experimental perfusion studies from the 1970s. These studies established that adenosine and AMP are probable mediators of exercise hyperemia in canine hindlimb muscles, with release increasing under constant flow rate perfusion during exercise and reactive hyperemia. A companion study evaluated the roles of potassium, inorganic phosphate, osmolarity, pH, pCO2, pO2, and adenosine or AMP in the same hyperemic responses. The properties of exercise and reactive hyperemias under constant pressure perfusion were characterized separately. These studies used isolated perfused preparations, and their relevance to clinical muscle disease in intact dogs is indirect. The findings inform understanding of blood flow regulation but do not provide diagnostic thresholds or treatment targets.

Expert opinion still differs on the clinical significance of thermographic findings. The pilot study noted that the right biceps femoris temperatures were higher than the left using linear region-of-interest analysis before and after walks, a finding that may reflect normal asymmetry or measurement artefact. Whether thermography can reliably distinguish neurogenic atrophy from disuse atrophy remains unresolved. Electrodiagnostic testing remains the reference standard for confirming denervation, but it requires general anesthesia or heavy sedation, specialised equipment, and an experienced operator. The MSD Veterinary Manual provides practical guidance on neuromuscular examination and electrodiagnostic interpretation for practitioners.

Referral, Consultation, and Reporting

Referral to a veterinary neurologist or surgeon is warranted when a pelvic limb nerve deficit does not improve within two to three weeks, when muscle atrophy progresses despite conservative management, or when a penetrating wound or fracture is associated with the deficit. Electrodiagnostic consultation is indicated to confirm denervation, to map the extent of nerve injury, and to establish a baseline for serial reassessment. Laboratory involvement may be required to rule out metabolic myopathies, though these are outside the scope of this article. The AVMA practice resources offer guidance on professional conduct and referral communication.

Regulatory reporting is rarely required for pelvic limb muscle conditions in companion animals. However, if a suspected adverse reaction to a veterinary medicinal product causes muscle dysfunction, the responsible veterinarian should report the event through the applicable national pharmacovigilance system. International standards for animal health and welfare, including those published by the World Organization for Animal Health, may apply in specific contexts such as working dogs or animals in trade. The NCBI Bookshelf collection provides access to comparative biomedical texts that can support further study of muscle physiology and pathology.

Frequently Asked Questions

How Do I Distinguish Sciatic From Femoral Nerve Dysfunction When Advanced Imaging Is Unavailable?

The physical examination provides the most reliable separation. Femoral nerve dysfunction abolishes the quadriceps reflex and produces an inability to extend the stifle, so the limb bears weight with a dropped stifle. Sciatic dysfunction spares the quadriceps reflex but abolishes the withdrawal reflex below the stifle, and the hock cannot flex during the withdrawal response. The peroneal branch of the sciatic nerve supplies the cranial tibial muscles, so loss of hock flexion with intact stifle extension points to sciatic involvement. Cutaneous sensation over the medial crus is femoral territory, while the lateral crus and dorsal paw are sciatic territory. Proprioceptive placing deficits appear with either lesion and do not discriminate.

What Is the Most Practical Way to Assess Pelvic Limb Muscle Function in a Fractious or Uncooperative Dog?

Sedation changes muscle tone and reflex thresholds, so examination before sedation is preferable whenever safe. For a fractile dog, observe the animal moving freely in a run or examination room before handling. Video recording permits frame-by-frame assessment of stance phase and swing phase without repeated restraint. After sedation, the examiner can still evaluate muscle bulk by palpation and measure limb circumference with a tape at reproducible landmarks, such as 5 cm proximal to the patella. Withdrawal reflexes remain testable under light sedation but become unreliable at deeper planes. If the dog cannot be examined safely without chemical restraint, document the pre-sedation gait findings and the post-sedation reflex findings separately in the record.

How Should I Document Serial Muscle Atrophy Measurements in the Medical Record?

Record the measurement site, the limb side, and the exact distance from a bony landmark for every assessment. For the quadriceps, measure thigh circumference at a fixed distance proximal to the proximal pole of the patella. For the hamstrings, measure at a fixed distance distal to the ischiatic tuberosity. Use a spring-loaded tape to standardize tension. Record the values in centimetres to one decimal place, and note the dog's body condition score at each visit because weight change confounds circumference trends. Photographs taken from a caudal view with the dog standing squarely on both hindlimbs provide a permanent visual record. Include the date, examiner initials, and the dog's activity level in the preceding week, since disuse alone can reduce thigh circumference measurably.

What Should I Tell an Owner Whose Dog Has a Suspected Sciatic Nerve Injury?

Explain that the sciatic nerve supplies most of the muscles that flex the hock and extend the hip, and that injury produces a dropped hock and knuckling of the paw. Describe the expected timeline: nerve recovery is slow, often requiring weeks to months, and depends on whether the nerve was compressed, stretched, or severed. Advise the owner to protect the dorsal paw from abrasion with a boot or bandage while knuckling persists. Explain that physiotherapy, including passive range of motion of the hock and stifle, helps preserve joint mobility while innervation returns. Set realistic expectations: some dogs regain full function, while others retain a permanent gait abnormality. Refer to MSD Veterinary Manual professional resources for general guidance on neurologic examination and prognosis.

How Does Pelvic Limb Muscle Assessment Differ in a Puppy Compared With an Adult Dog?

Puppies have less defined muscle contours, so subtle atrophy is harder to appreciate by inspection alone. Palpation and circumferential measurement are more reliable than visual assessment in young dogs. Reflexes are brisk in puppies, and a normal crossed extensor response may persist up to several months of age, so its presence does not indicate upper motor neuron disease as it would in an adult. Gait immaturity can mimic mild proprioceptive ataxia, particularly in large-breed puppies under six months. Serial examinations are more informative than a single assessment in a growing dog, because normal development changes the baseline. When a puppy presents with progressive pelvic limb weakness, distinguish developmental orthopedic disease from neurologic causes before attributing the signs to nerve injury.

When Should I Refer a Pelvic Limb Muscle Case instead of Continue Managing It in Primary Care?

Refer when the neurologic deficit is progressive, when it involves more than one nerve territory, or when the dog is non-ambulatory for more than 48 hours despite supportive care. Acute onset of paraparesis with absent deep pain perception in the pelvic limbs is an emergency that warrants immediate referral for advanced imaging. Refer also when muscle atrophy is rapid and severe, when there is suspected nerve root or spinal cord involvement, or when electrodiagnostic testing is needed to confirm the distribution of denervation. If the owner declines referral, document the discussion and the recommended monitoring plan. The AVMA professional practice resources provide guidance on referral communication and continuity of care.

Related Clinical & Scientific Guides

• Canine Respiratory System: Anatomy and Physiology
• Comparative Anatomy of the Mammalian Kidney
• Feline Cardiopulmonary Physiology: Heart-Lung Interactions

References and Further Reading

• Role of adenosine or AMP as a probable mediator of blood flow regulation in canine hindlimb muscles.. 1975.
• Evaluation of Thermographic Imaging in Canine Hindlimb Muscles After 6 Min of Walking-A Pilot Study.. 2020.
• Evaluation of roles of potassium, inorganic phosphate, osmolarity, pH, pCO2, pO2, and adenosine or AMP in exercise and reactive hyperemias in canine hindlimb muscles.. 1973.
• Properties of exercise and reactive hyperemias in canine hindlimb muscles under constant pressure perfusion.. 1973.
• NCBI Bookshelf: Veterinary and Comparative Biomedical Sciences. NCBI Bookshelf.
• MSD Veterinary Manual, Professional Edition. MSD Veterinary Manual.
• American Veterinary Medical Association Practice Resources. American Veterinary Medical Association.
• WOAH Terrestrial Animal Health Code. WOAH.

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This article is educational professional reference material for veterinary audiences. It is not a substitute for veterinary diagnosis, individual clinical judgment, current product labeling, or applicable regulatory requirements.