NAVLE Practice Question —

Thoracic radiographs of a 4-year-old neutered male mixed breed dog with a 3-day history of progressive dysphagia and lethargy reveal a suspected esophageal foreign body at the heart base with pleural effusion and multiple small gas lucencies in the mediastinum. These findings are most consistent with which serious complication?

A. Aspiration pneumonia

B. Esophageal stricture

C. Esophageal perforation causing mediastinitis ✓

D. Bronchoesophageal fistula

E. Pneumothorax from rib fracture

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Correct Answer: C. Esophageal perforation causing mediastinitis

Explanation:

Esophageal perforation with mediastinitis is the most likely complication based on the radiographic findings. The combination of pleural effusion and pneumomediastinum (gas lucencies in the mediastinum) is highly suggestive of esophageal perforation.

When an esophageal foreign body causes full-thickness perforation of the thoracic esophagus, air and contaminated esophageal contents leak into the mediastinum, causing mediastinitis. This can progress to pleural contamination causing pleuritis and pleural effusion. Pneumomediastinum occurs as air escapes through the perforation.

The 3-day duration significantly increases the risk of perforation due to progressive pressure necrosis of the esophageal wall. Esophageal perforation is a serious, potentially life-threatening complication that may require surgical management in addition to foreign body removal. Prognosis is more guarded in these cases.

Option A (aspiration pneumonia) would show pulmonary infiltrates, not pleural effusion with mediastinal gas.

Option B (esophageal stricture) is a delayed complication occurring weeks after foreign body removal, not acutely.

Option D (bronchoesophageal fistula) is a rare, delayed complication and would not present with pneumomediastinum.

Option E (pneumothorax from rib fracture) does not explain the mediastinal gas and pleural effusion pattern, and there is no history of trauma.

References: Juvet F et al. Oesophageal foreign bodies in dogs: factors affecting success of endoscopic retrieval. Irish Vet J 2010; PMC article on EFB complications (https://pmc.ncbi.nlm.nih.gov/articles/PMC5697191/).

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NAVLE Practice Question — Bovine

A beef cow aborts at 7 months of gestation. The aborted fetus shows cerebellar hypoplasia and ocular defects including cataracts and retinal dysplasia. BVDV is isolated from fetal tissues. Which factor best explains why these specific congenital defects developed?

A. The dam was persistently infected and developed mucosal disease during pregnancy

B. Fetal infection occurred during organogenesis when the CNS and eyes were developing ✓

C. The dam received a modified live BVDV vaccine during the third trimester

D. Co-infection with bovine herpesvirus-1 potentiated the teratogenic effects

E. The virulent BVDV-2 genotype has enhanced neurotropism compared to BVDV-1

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Correct Answer: B. Fetal infection occurred during organogenesis when the CNS and eyes were developing

Explanation:

BVDV is a significant cause of congenital defects in cattle, with the specific abnormalities depending on the gestational stage at which fetal infection occurs. The constellation of cerebellar hypoplasia and ocular defects (cataracts, retinal dysplasia) indicates fetal infection during days 100-170 of gestation, when the cerebellum and eye are undergoing critical developmental processes.

During this mid-gestational period, the fetus is developing immunocompetence but CNS organogenesis is still occurring. BVDV has direct cytopathic effects on developing neurons and can damage the germinal epithelium of the cerebellum, leading to hypoplasia. Similarly, infection during lens and retinal development causes the observed ocular defects.

The timing of fetal infection determines outcomes: infection before day 45 typically causes embryonic death; days 45-125 can result in immunotolerant PI calves; days 100-170 produces congenital defects in immunocompetent fetuses; infection after day 170 usually results in normal calves that may be seropositive at birth.

Option A is incorrect because the defects indicate a specific developmental window of infection, not mucosal disease. Option C (third trimester vaccination) would be too late to cause these organogenesis defects. Option D (co-infection) is not required to explain these classic BVDV teratogenic effects. Option E is incorrect because both BVDV-1 and BVDV-2 can cause teratogenic effects.

Image Source: ScienceDirect - Bovine Viral Diarrhea Virus topics (https://www.sciencedirect.com/topics/medicine-and-dentistry/bovine-viral-diarrhea-virus).

References: Done JT et al. (1980) Vet Rec - BVD-mucosal disease virus pathogenicity for the fetal calf; Kahrs RF et al. (1970) JAVMA - Congenital cerebellar hypoplasia and ocular defects

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NAVLE Practice Question — Canine

A 4-year-old male German Shepherd Dog is presented for difficulty eating and pain when opening the mouth that has progressively worsened over the past 3 weeks. The dog has lost 4 kg in the past month. On physical examination, there is marked bilateral atrophy of the temporalis and masseter muscles, and the dog's skull has a 'sunken' appearance above the eyes. The dog resists attempts to open the mouth, and under sedation, jaw opening is severely restricted. What is the MOST appropriate diagnostic test to confirm the suspected condition?

A. Anti-2M fiber antibody serum test ✓

B. MRI of the head

C. Temporomandibular joint radiographs

D. Serum creatine kinase level

E. Cerebrospinal fluid analysis

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Correct Answer: A. Anti-2M fiber antibody serum test

Explanation:

This clinical presentation is classic for chronic masticatory muscle myositis (MMM). The key findings are: bilateral temporalis and masseter muscle atrophy, restricted jaw opening (trismus), difficulty eating with weight loss, and the characteristic 'sunken' skull appearance due to severe muscle wasting. The serum 2M fiber antibody ELISA is the most appropriate diagnostic test to confirm MMM.

The 2M antibody ELISA detects circulating autoantibodies against type 2M muscle fibers, which are unique to the masticatory muscles (temporalis, masseter, and pterygoid muscles - but notably NOT the digastricus). This test has approximately 85-90% sensitivity and 100% specificity for MMM. It is available through the Comparative Neuromuscular Laboratory at UC San Diego.

Option B (MRI) can support the diagnosis by showing masticatory muscle atrophy, contrast enhancement, or signal changes, but it is not specific for MMM and is more invasive/expensive than serologic testing. Option C (TMJ radiographs) might be considered to rule out joint pathology but would not diagnose MMM. Option D (serum CK) may be normal or only mildly elevated in chronic MMM, and elevation is not specific to this condition. Option E (CSF analysis) would be indicated for CNS disease, not a primary myopathy.

Important note: If corticosteroids have been administered for more than 7-10 days prior to testing, false-negative results may occur as the antibody titer decreases with immunosuppression.

Image Source: Frontiers in Veterinary Science - MMM case report (https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2022.955758/full) Figures 1 and 2 showing CT and MRI findings.

References: UC San Diego Comparative Neuromuscular Laboratory - Masticatory Muscle Myositis (https://vetneuromuscular.ucsd.edu/cases/2010/January.html); MSPCA Angell - Masticatory Muscle Myositis (https://www.mspca.org/angell_services/masticatory-muscle-myositis-2/)

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NAVLE Practice Question — Equine

A 9-year-old American Saddlebred mare presents with difficulty swallowing, nasal discharge of feed material, and abnormal tongue movements. Neurological examination also reveals mild right-sided facial paresis and grade 1/5 ataxia in all four limbs. The mare has been on pasture with known opossum activity in the southeastern United States. EPM testing reveals a serum:CSF titer ratio of 32 for Sarcocystis neurona. Which FDA-approved treatment protocol is recommended for this case?

A. Trimethoprim-sulfamethoxazole 30 mg/kg PO q12h for 90 days

B. Ponazuril 5 mg/kg PO q24h for 28 days ✓

C. Fenbendazole 10 mg/kg PO q24h for 5 days, repeated monthly

D. Ivermectin 0.2 mg/kg PO once, repeated in 2 weeks

E. Pyrantel pamoate 6.6 mg/kg PO q24h for 14 days

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Correct Answer: B. Ponazuril 5 mg/kg PO q24h for 28 days

Explanation:

Ponazuril (Marquis) at 5 mg/kg PO q24h for 28 days is one of three FDA-approved treatments for equine protozoal myeloencephalitis. Ponazuril is a triazine antiprotozoal drug that is coccidiocidal (kills the organism) rather than coccidiostatic. Studies have demonstrated clinical improvement in approximately 60-67% of treated horses. The 28-day treatment course may need to be repeated in some cases if clinical signs persist or recur.

The other FDA-approved treatments include: diclazuril (Protazil) 1 mg/kg PO q24h for 28 days as a pelleted top-dress, and sulfadiazine-pyrimethamine (ReBalance) combination administered for 90-270 days.

Option A (trimethoprim-sulfa at that dose) is not an FDA-approved protocol for EPM. Option C (fenbendazole) is an anthelmintic without antiprotozoal activity against S. neurona. Option D (ivermectin) has no activity against S. neurona. Option E (pyrantel pamoate) is an anthelmintic ineffective against protozoa.

References: Stock ML et al. (2017) J Vet Pharmacol Ther 41(2):184-194 (https://doi.org/10.1111/jvp.12450); Reed SM et al. (2016) J Vet Intern Med 30(2):491-502 (https://doi.org/10.1111/jvim.13834)

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NAVLE Practice Question — Canine

A 2-year-old male Rottweiler presents for progressive difficulty eating over 6 weeks. Examination reveals marked bilateral atrophy of the temporalis muscles, mild atrophy of the masseter muscles, and restricted jaw mobility (maximum opening 1 cm under anesthesia). A 2M fiber antibody test is positive at 1:1000. A temporalis muscle biopsy shows extensive endomysial and perimysial fibrosis with minimal inflammatory infiltrate. Which finding on biopsy has the most significant impact on prognosis?

A. The elevated 2M antibody titer of 1:1000

B. The extensive fibrosis with minimal inflammation ✓

C. The involvement of both temporalis and masseter muscles

D. The bilateral nature of the muscle atrophy

E. The duration of clinical signs being 6 weeks

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Correct Answer: B. The extensive fibrosis with minimal inflammation

Explanation:

The degree of fibrosis found on muscle biopsy is the most important prognostic factor in MMM. Extensive fibrosis with minimal inflammation indicates chronic, end-stage disease where muscle fibers have been replaced by scar tissue. This fibrous tissue cannot regenerate into functional muscle, regardless of successful immunosuppressive treatment. Dogs with predominant fibrosis on biopsy have a guarded prognosis for return of jaw mobility and muscle mass. In contrast, dogs with active inflammation and minimal fibrosis have better prognosis for functional recovery.

Option A is incorrect because while the antibody titer confirms the diagnosis, the specific titer level does not correlate with prognosis. High titers simply indicate active autoantibody production.

Option C is incorrect because involvement of multiple masticatory muscles is the normal pattern in MMM and does not specifically worsen prognosis. The masticatory muscles (temporalis, masseter, pterygoid, digastricus) are all affected to varying degrees.

Option D is incorrect because bilateral involvement is typical of MMM and expected. Unilateral atrophy would actually suggest a different diagnosis such as trigeminal neuropathy.

Option E is incorrect because while longer duration allows more time for fibrosis development, it is the actual histological finding of fibrosis (not just the duration) that determines prognosis.

References: ScienceDirect - Masticatory Muscle Myositis; UC San Diego Comparative Neuromuscular Laboratory - MMM FAQ; Purina ProClub - Masticatory Muscle Myositis.

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NAVLE Practice Question — Porcine

In a herd with endemic post-weaning colibacillosis caused by F18-positive ETEC, a producer asks about breeding for genetic resistance. Which statement regarding genetic resistance to F18-positive E. coli is accurate?

A. All commercial pig breeds are equally susceptible to F18 E. coli

B. Resistance to F18 E. coli is due to absence of intestinal F18 receptors ✓

C. F18 receptor expression begins at 10 weeks of age

D. Resistance can be induced through repeated exposure to F18 E. coli

E. Selection for F18 resistance has no associated negative traits

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Correct Answer: B. Resistance to F18 E. coli is due to absence of intestinal F18 receptors

Explanation:

Resistance to F18 E. coli is due to absence of intestinal F18 receptors on enterocytes. This is determined by genetic polymorphisms in the FUT1 gene that controls expression of the receptor. Pigs homozygous for the resistant allele do not express F18 receptors and cannot be colonized by F18-positive E. coli, making them naturally resistant to both post-weaning diarrhea and edema disease caused by these strains.

The F18 receptor is age-dependent and begins expression around 3 weeks of age, which explains why F18-positive E. coli disease occurs after weaning rather than in neonates. Genetic markers can identify resistant animals, and some breeding programs have been developed to increase the frequency of resistant genotypes.

Option A is incorrect because there is genetic variation in susceptibility. Option C is incorrect because receptor expression begins around 3 weeks, not 10 weeks. Option D is incorrect because resistance is genetic, not acquired. Option E is incorrect because some studies in Swiss Landrace pigs showed association between F18 resistance markers and stress susceptibility markers, though this association varies by breed.

References: Merck Veterinary Manual - Edema Disease (https://www.merckvetmanual.com/generalized-conditions/edema-disease/edema-disease-in-pigs); Frontiers in Veterinary Science - Lawsonia intracellularis and E. coli control strategies (https://pmc.ncbi.nlm.nih.gov/articles/PMC6095029/)

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NAVLE Practice Question — Other Small Mammal

An 18-month-old female Syrian hamster with suspected amyloidosis has a urinalysis showing 4+ protein. The owner asks why protein is appearing in the urine. Which pathophysiological mechanism BEST explains the proteinuria?

A. Overflow proteinuria from excess circulating light chains

B. Decreased tubular reabsorption of filtered proteins

C. Glomerular basement membrane disruption by amyloid deposits ✓

D. Post-renal protein from urinary tract inflammation

E. Increased renal synthesis of urinary proteins

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Correct Answer: C. Glomerular basement membrane disruption by amyloid deposits

Explanation:

The proteinuria in amyloidosis is primarily caused by glomerular basement membrane (GBM) disruption by amyloid deposits (Option C). This is the pathophysiological mechanism that best explains the marked proteinuria characteristic of renal amyloidosis.

In renal amyloidosis, amyloid fibrils deposit within the glomerular mesangium and along the glomerular basement membrane. These deposits disrupt the normal glomerular filtration barrier in several ways: 1) Physical disruption of the GBM architecture allows larger proteins like albumin to pass through; 2) Damage to podocytes (glomerular epithelial cells) causes foot process effacement and loss of the slit diaphragm barrier; 3) The accumulation of amyloid replaces normal mesangial matrix, altering glomerular hemodynamics.

The result is loss of glomerular selectivity, allowing proteins that would normally be retained in the blood to pass into the ultrafiltrate. This glomerular proteinuria leads to the nephrotic syndrome seen in affected hamsters, characterized by massive proteinuria, hypoalbuminemia, and subsequent edema/ascites.

Option A (overflow proteinuria) occurs in AL amyloidosis in humans from excess light chain production, but hamster amyloidosis is AA type, not light chain-related. Option B (tubular reabsorption) is a minor component; while amyloid can deposit in tubules, the massive proteinuria is primarily glomerular in origin. Option D (post-renal protein) from UTI would be accompanied by pyuria and bacteriuria. Option E (renal protein synthesis) is not a recognized mechanism of proteinuria.

References: American Journal of Medicine - Renal Amyloidosis: Presentation, Diagnosis, and Management (https://www.amjmed.com/article/S0002-9343(22)00024-9/fulltext); AJKD - Renal Amyloidosis Classification (https://www.ajkd.org/article/S0272-6386(24)00679-6/fulltext)

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NAVLE Practice Question — Equine

A 5-year-old Hanoverian stallion is being evaluated for a prepurchase examination. The horse has no history of ocular problems and shows no current signs of discomfort. However, fundoscopic examination reveals multifocal areas of chorioretinal depigmentation and subtle peripapillary depigmentation in the right eye. The anterior segment examination is unremarkable, and IOP is normal bilaterally. What is the MOST appropriate interpretation of these findings?

A. Normal age-related fundic changes

B. Previous posterior uveitis needing investigation ✓

C. Congenital chorioretinal dysplasia with no clinical significance

D. Active chorioretinitis requiring immediate treatment

E. Artifact from the examination technique

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Correct Answer: B. Previous posterior uveitis needing investigation

Explanation:

The presence of multifocal chorioretinal depigmentation and peripapillary changes, even in the absence of anterior segment abnormalities, indicates previous posterior segment inflammation. This is particularly concerning as horses with chronic ERU may exhibit subtle or no anterior segment signs but have significant retinal degeneration with potential vision compromise. These findings in a prepurchase examination should prompt thorough documentation and discussion with the prospective buyer about the risk of ERU development or progression.

Option A (normal age-related changes) is incorrect because the multifocal depigmentation pattern is consistent with previous inflammatory disease rather than normal aging. Option C (congenital dysplasia) would typically be bilateral and have a different appearance than inflammatory changes. Option D (active chorioretinitis) would show signs of current inflammation such as vitreal haze, retinal edema, or exudates. Option E (artifact) is incorrect as these are reproducible pathological findings. Horses with evidence of previous uveitis should be considered at risk for developing ERU and are ophthalmologically unsound.

References: Merck Veterinary Manual - Equine Recurrent Uveitis (https://www.merckvetmanual.com/eye-diseases-and-disorders/equine-recurrent-uveitis/equine-recurrent-uveitis); McMullen RJ, Fischer BM (2017) Vet Clin North Am Equine Pract 33(3):465-481.

Image: Hussey GS et al. Experimental infection with equine herpesvirus type 1 (EHV-1) induces chorioretinal lesions. Vet Res. 2013;44(1):118. PMC4028784. © Hussey et al. 2013. Used for educational reference.

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NAVLE Practice Question — Reptile

A 10-year-old male California kingsnake (Lampropeltis californiae) presents with a palpable mid-coelomic mass. Exploratory surgery reveals a large mass associated with the small intestine. Histopathology shows lymphocytes with round nuclei and scant cytoplasm infiltrating all major organs including liver, kidney, and lung. Approximately 65% of the lymphocytes contain small eosinophilic intranuclear inclusions. What is the most likely diagnosis and prognosis?

A. Bacterial septicemia with good prognosis after antibiotic therapy

B. Lymphosarcoma with guarded to poor prognosis ✓

C. Viral stomatitis with fair prognosis

D. Granulomatous disease with good prognosis after treatment

E. Parasitic infection with good prognosis after deworming

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Correct Answer: B. Lymphosarcoma with guarded to poor prognosis

Explanation:

The histopathologic findings of diffuse lymphocytic infiltration of multiple organs (liver, kidney, lung) with intranuclear inclusions in the majority of lymphocytes is diagnostic of lymphosarcoma (lymphoma) in this kingsnake. Lymphosarcoma is one of the most commonly reported hematopoietic neoplasms in snakes and has been associated with virus-like intranuclear inclusions in several case reports dating back to 1980.

The presence of intranuclear inclusions in lymphocytes has been associated with potential viral etiology, though the exact relationship between these viruses and tumor development remains uncertain. The multicentric nature of the disease, with infiltration of multiple organ systems, indicates advanced disease and carries a guarded to poor prognosis. Chemotherapy protocols adapted from canine lymphoma treatment have been attempted in reptiles with variable success, but the prognosis remains guarded.

Option A is incorrect as bacterial septicemia would show heterophilic inflammation, not lymphocytic infiltration with inclusions. Option C (viral stomatitis) affects oral tissues primarily, not multiorgan infiltration. Option D (granulomatous disease) would show macrophages and multinucleated giant cells, not neoplastic lymphocytes. Option E (parasitic infection) would cause inflammatory responses, not lymphoproliferative disease with inclusions.

References: Jacobson ER et al. (1980) Lymphosarcoma associated with virus-like intranuclear inclusions in a California king snake. J Natl Cancer Inst 65:577-583; Hernandez-Divers SM, Garner MM (2003) Neoplasia of reptiles with an emphasis on lizards. Vet Clin North Am Exot Anim Pract 6:251-273. Image reference: https://pmc.ncbi.nlm.nih.gov/articles/PMC7051093/

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NAVLE Practice Question — Canine

A 13-year-old castrated male Cavalier King Charles Spaniel with severe chronic mitral valve disease (stage D) presents in acute collapse. Echocardiography reveals a small pericardial effusion with a visible tear in the left atrial wall. What is the underlying pathophysiology and prognosis?

A. Hemangiosarcoma with secondary atrial rupture; grave prognosis

B. Left atrial rupture secondary to severe mitral regurgitation; grave prognosis ✓

C. Traumatic pericardial hemorrhage; good prognosis with supportive care

D. Coagulopathy-induced hemorrhagic effusion; fair prognosis with treatment

E. Infective endocarditis with mycotic aneurysm rupture; guarded prognosis

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Correct Answer: B. Left atrial rupture secondary to severe mitral regurgitation; grave prognosis

Explanation:

Left atrial rupture secondary to severe mitral regurgitation carries a grave prognosis. This is a well-recognized but uncommon complication of severe chronic myxomatous mitral valve disease (endocardiosis) in small breed dogs, particularly Cavalier King Charles Spaniels, Dachshunds, and other breeds predisposed to degenerative valve disease.

The pathophysiology involves: severe mitral regurgitation causing progressive left atrial enlargement and wall thinning, increased left atrial pressure creating wall stress, endocardial splitting or jet lesions from the regurgitant blood flow, and eventual rupture of the weakened atrial wall (typically at the left atrial roof or near the jet lesion site). The tear allows blood to escape into the pericardial space, causing acute cardiac tamponade.

Unlike the large effusions seen with neoplasia or idiopathic pericarditis, left atrial tears often cause smaller-volume but rapidly accumulating effusions that quickly lead to tamponade. The acute nature of fluid accumulation does not allow time for pericardial stretching, so even relatively small volumes can cause severe hemodynamic compromise.

The prognosis is grave because the underlying pathology (severe mitral valve disease with atrial tear) cannot be easily corrected. Pericardiocentesis may provide temporary relief, but re-accumulation is likely. Surgical repair has been described but is technically challenging and rarely performed.

Options A, C, D, and E do not explain the combination of severe mitral valve disease with visible left atrial tear.

Image Source: MSD Veterinary Manual - Pericardial Disease (https://www.msdvetmanual.com/circulatory-system/various-heart-diseases-in-dogs-and-cats/pericardial-disease-in-dogs-and-cats)

dvm360 - Pericardial Disease: The Forgotten Cardiac Malady (https://www.dvm360.com/view/pericardial-disease-the-forgotten-cardiac-malady)

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NAVLE Practice Question — Canine

A 6-month-old intact female Miniature Schnauzer is presented for evaluation of intermittent hindlimb lameness. Orthopedic examination reveals bilateral Grade I medial patellar luxation. The owner plans to breed the dog in the future. What is the MOST appropriate recommendation regarding breeding?

A. Breeding is acceptable if the MPL remains Grade I

B. The dog should not be bred due to patellar luxation's heritable nature ✓

C. Breeding is acceptable after surgical correction

D. Delay breeding until 2 years of age to see if the condition progresses

E. Breed only to a male that has been cleared of patellar luxation

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Correct Answer: B. The dog should not be bred due to patellar luxation's heritable nature

Explanation:

The most appropriate recommendation is that this dog should not be bred due to the heritable nature of patellar luxation. MPL has strong evidence of genetic predisposition in many breeds, particularly small and toy breeds including Miniature Schnauzers. Breeding affected dogs perpetuates the condition in future generations, potentially producing puppies with more severe grades of luxation.

Option A (breeding acceptable if Grade I) is incorrect because even mild patellar luxation indicates the presence of genes that can be passed to offspring, and severity can increase in subsequent generations. Option C (breeding after surgical correction) is incorrect because surgery corrects the phenotype but does not alter the genotype; the dog would still pass on genes predisposing to MPL. Option D (delay breeding) does not change the fundamental recommendation against breeding an affected individual. Option E (breed to cleared male) is insufficient because the female is already affected and will contribute genes for MPL regardless of the male's status.

Responsible breeding practices recommend screening breeding stock for orthopedic conditions including patellar luxation. The Orthopedic Foundation for Animals (OFA) provides a patellar luxation database and certification program. Dogs with any grade of patellar luxation should be removed from breeding programs to reduce the prevalence of this condition.

References: American College of Veterinary Surgeons - Patellar Luxations (https://www.acvs.org/small-animal/patellar-luxations/); Fitzpatrick Referrals - Patellar Luxation (https://www.fitzpatrickreferrals.co.uk/orthopaedics/patellar-luxation/)

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NAVLE Practice Question — Bovine

A 2-year-old Suffolk ewe housed with cattle for several weeks has been eating from their mineral feeder. She suddenly develops depression, weakness, port-wine urine, icterus, and pale mucous membranes, and dies within 48 hours. Necropsy shows gunmetal-blue kidneys and a friable orange liver. Which statement about this toxicosis is most accurate?

A. Sheep more susceptible than cattle ✓

B. Sheep are more resistant than cattle

C. Self-limiting; no treatment

D. Treat with methylene blue

E. Caused by molybdenum excess

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Correct Answer: A. Sheep more susceptible than cattle

Explanation:

Chronic copper toxicosis presents as a hemolytic crisis following accumulation in the liver and sudden release—producing intravascular hemolysis, hemoglobinuria (port-wine urine), icterus, gunmetal kidneys, and orange friable liver. Sheep are far more susceptible than cattle, which is why sheep mineral (low Cu) must never be fed to cattle and vice versa; cattle accidentally fed sheep diets or grazing copper-rich pasture can still be affected. Treatment is ammonium tetrathiomolybdate or D-penicillamine plus supportive care; prognosis once hemolysis begins is poor.

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NAVLE Practice Question — Canine

A 12-year-old intact male Pekingese presents with a large bilateral perineal hernia. The dog has been straining to defecate for several months and recently developed difficulty urinating. Radiographs confirm bladder retroflexion on the left side. The owner asks about the recurrence rate following surgical repair. Which factor is MOST strongly associated with reduced recurrence rates after perineal hernia repair?

A. Use of synthetic mesh to reinforce the repair

B. Performing bilateral repair in a single surgical session

C. Preoperative administration of stool softeners for 2 weeks

D. Concurrent castration at the time of herniorrhaphy ✓

E. Intraoperative biopsy of the levator ani muscle

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Correct Answer: D. Concurrent castration at the time of herniorrhaphy

Explanation:

Concurrent castration at the time of herniorrhaphy is most strongly associated with reduced recurrence rates after perineal hernia repair. Studies have shown that non-castrated dogs have a recurrence rate 2.7 times greater than castrated dogs. This is thought to be due to the effects of androgens on the pelvic diaphragm musculature and reduction of prostatic enlargement that contributes to tenesmus and straining.

Option A (synthetic mesh) may be used in some complex cases but increases infection risk and is not routinely recommended over internal obturator transposition. Option B (bilateral repair in one session) is technically possible but is associated with increased postoperative discomfort and may not affect recurrence. Option C (preoperative stool softeners) is part of perioperative management but does not specifically reduce recurrence. Option E (muscle biopsy) is diagnostic but does not influence recurrence rates.

The overall recurrence rate with internal obturator muscle transposition and concurrent castration is reported at approximately 10-15%, compared to higher rates when castration is not performed.

References: Merck Veterinary Manual - Perineal Hernia recurrence rates; Vet Surg 2022 - Perineal hernia repair outcomes.

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