NAVLE Urinary

Bovine Urolithiasis Study Guide

📅 March 28, 2026 ⏱ 25 min read

Obstructive urolithiasis is a major cause of morbidity and death in male ruminants, ranking as the fifth most prevalent cause of death in feedlot cattle.

Overview and Clinical Importance

Obstructive urolithiasis is a major cause of morbidity and death in male ruminants, ranking as the fifth most prevalent cause of death in feedlot cattle. The condition results from the formation of urinary calculi (uroliths) that obstruct the urinary tract, most commonly at the sigmoid flexure of the penis in cattle. Early recognition and treatment are critical for achieving positive outcomes, as untreated obstruction leads to bladder or urethral rupture within 24-48 hours.

This condition carries significant economic implications in feedlot operations and represents a commonly tested topic on the NAVLE. Understanding the pathophysiology, urolith types, clinical presentation, and treatment options is essential for veterinary practice.

Urolith Type	Dietary Association	Urine pH	Characteristics
Struvite (Magnesium Ammonium Phosphate)	High-grain diets, pelleted rations, low forage intake	Alkaline (7.2-8.4)	Most common in feedlot cattle; soft, easily crushable; multiple small stones
Calcium Carbonate	Legume hay (alfalfa, clover), high-calcium diets	Alkaline	Gold-colored beads; very stable structure; radiopaque on radiography
Silicate	Grazing silicaceous pastures (western US/Canada)	pH independent	Usually singular; affects all ages and sexes; silica content increases as grasses mature
Calcium Oxalate	Oxalate-containing plants (sugar beet tops, greasewood)	pH independent	Less common in cattle; associated with specific plant ingestion
Calcium Phosphate (Apatite)	High-grain diets similar to struvite	Alkaline (6.5-7.5)	Often found with struvite; feedlot cattle

Etiology and Pathophysiology

Urolith Formation

Urinary calculi formation is a multifactorial process occurring in three phases: (1) formation of an organic nidus (matrix of mucoproteins and epithelial cells), (2) supersaturation of urine with mineral components, and (3) precipitation of crystals around the nidus. Crystal formation occurs when the inhibitory capacity of mucopolysaccharides, ions, and organic acids in urine is exceeded.

Types of Uroliths in Cattle

Risk Factors

Anatomical Factors

Long, narrow sigmoid-shaped urethra: The bovine male urethra is long and has an S-shaped curve (sigmoid flexure) where uroliths commonly lodge
Early castration: Results in decreased urethral diameter due to lack of testosterone; steers 8-12 months old are at highest risk; delaying castration until at least 6 months may reduce risk
Distal sigmoid flexure: Most common site of obstruction in cattle near the insertion of the retractor penis muscle

Dietary Factors

Calcium:Phosphorus imbalance: Ratio less than 2:1 predisposes to phosphatic stones; high phosphorus in grains (corn, wheat, sorghum)
High-concentrate/low-forage diets: Reduced saliva production decreases phosphorus excretion via GI tract, increasing urinary phosphorus
High magnesium intake: Should not exceed 0.6% of total ration; contributes to struvite formation
Pelleted rations: Decrease saliva production, reducing phosphorus excretion through the GI tract

Water and Environmental Factors

Decreased water intake: Leads to concentrated urine; seasonal influence with higher incidence in late fall/winter and arid summer months
Water quality: High mineral content in water may contribute to urolith formation
Low salt intake: Reduces water consumption and urine output

NAVLE TipRemember 'FEEDLOT STEERS = STRUVITE' - the classic NAVLE scenario involves a young castrated male on a high-grain feedlot diet. Also remember: 'Ca:P ratio of 2:1 is the TARGET' - anything less than 2:1 predisposes to phosphatic stones.

Stage	Key Clinical Signs	Physical Exam Findings
Early Obstruction	Stranguria, dysuria, colic signs, tail swishing, restlessness	Distended bladder, calculi on preputial hairs, urethral pulsations
Urethral Rupture	Temporary relief then decline, anorexia, depression	Subcutaneous swelling ventral abdomen and perineum, peri-penile edema
Bladder Rupture	Progressive abdominal distension, weakness, uremic breath	Fluid wave on ballottement, empty bladder on rectal exam

Clinical Signs and Presentation

Early Obstruction (0-24 hours)

Frequent posturing to urinate with minimal to no urine production
Tail swishing and restlessness
Stranguria (straining to urinate) and dysuria
Signs of colic: bruxism (teeth grinding), stretching, treading hind feet, kicking at abdomen
Hematuria (blood in urine) if partial obstruction
Calculi or blood visible on preputial hairs - a key physical exam finding
Palpable pulsations of the pelvic urethra on rectal examination
Distended urinary bladder palpable per rectum

Advanced Obstruction and Rupture (more than 24-48 hours)

Urethral Rupture

Subcutaneous swelling ventral to the anus and perineum extending to the ventral abdomen
Peri-penile edema
Urine pooling subcutaneously - 'water belly' appearance
Initial apparent relief of discomfort followed by progressive deterioration

Bladder Rupture (Cystorrhexis)

Progressive abdominal distension - 'water belly' or 'uroabdomen'
Ballotable fluid wave in abdomen
Depression and weakness
Uremic odor to breath
Cattle can survive 2 weeks or more following bladder rupture before succumbing to uremia

Summary: Clinical Signs by Stage

Exam Focus: The NAVLE often presents scenarios asking you to differentiate obstruction from rupture. Key distinguishing feature: With obstruction, the bladder is DISTENDED on rectal exam; with rupture, the bladder is EMPTY but abdomen shows fluid accumulation.

Parameter	Expected Change	Clinical Significance
Creatinine	Elevated (most reliable)	Best indicator of renal function in ruminants
BUN	Elevated (less dramatic than monogastrics)	Ruminants excrete urea via rumen - elevations less pronounced
Phosphorus	Hyperphosphatemia	Common finding with obstruction
Potassium	Variable (often normal)	Ruminants excrete K+ via saliva - less accumulation
Sodium/Chloride	Hyponatremia, hypochloremia	Especially after bladder rupture

Diagnosis

Physical Examination

Rectal examination: Assess bladder distension, urethral pulsations, presence of nephroliths or ureteroliths
Palpation of the penis caudal to scrotum: May reveal location of large urethral calculi
Abdominal contour assessment: Evaluate for distension or ventral swelling
Preputial hair examination: Look for blood clots, crystals, or small stones

Serum Biochemistry

High-YieldUnlike dogs and cats, ruminants do NOT typically develop life-threatening hyperkalemia with urinary obstruction because they can excrete potassium via saliva. Creatinine is the most reliable indicator of renal impairment in cattle with urolithiasis.

Diagnostic Imaging

Ultrasonography

Ultrasonography is the most practical imaging modality for bovine urolithiasis. It can be performed transabdominally (inguinal region) or transrectally using a 5 MHz sector probe.

Assess bladder integrity, distension, and wall thickness
Detect free abdominal fluid (uroperitoneum)
Identify cystoliths, ureteroliths, or nephroliths
Evaluate for hydronephrosis or hydroureter
Detect peri-penile edema suggesting urethral rupture

Radiography

Calcium carbonate stones: Radiopaque - visible on survey radiographs
Phosphatic stones (struvite): Less radiopaque - often missed due to abdominal mass
Absence of visible uroliths on radiography does not rule out urolithiasis

Urinalysis

Hematuria, proteinuria, and alkalinuria are expected findings
Crystalluria may be present - crystal type helps guide treatment and prevention
Rule out concurrent bacterial cystitis or pyelonephritis

Confirming Uroperitoneum

Perform abdominocentesis and compare abdominal fluid creatinine to serum creatinine. A ratio greater than 2:1 (abdominal:serum) confirms uroperitoneum.

Treatment	Dosage	Purpose	Notes
Ammonium Chloride	200-350 mg/kg PO q24h	Urinary acidification	Target urine pH less than 6.5; dissolves struvite only
IV Fluid Therapy	Balanced crystalloids	Diuresis and azotemia correction	Continue 24-48 hours post-surgery
Flunixin Meglumine	1.1-2.2 mg/kg IV q24h	Analgesia and anti-inflammatory	Reduces urethral inflammation
Antibiotics	Procaine penicillin 22,000 IU/kg IM q12h or Ceftiofur 2.2 mg/kg SQ q24h	Prevent/treat UTI	Continue until 1 week after catheter removal
Smooth Muscle Relaxants	Acepromazine 0.05-0.1 mg/kg IV or IM	Urethral relaxation	Limited efficacy; historical use

Treatment

Treatment goals for cattle with urolithiasis include: (1) establishing urethral patency, (2) providing analgesia, (3) correcting fluid and electrolyte imbalances, (4) decreasing urethral inflammation, and (5) preventing infection.

Medical Management

Medical management may be attempted for partial obstructions only. Complete obstructions require surgical intervention.

Surgical Treatment Options

Surgery is usually required for complete obstruction. Choice of procedure depends on intended use (breeding vs. salvage), economic considerations, and severity of disease.

NAVLE TipFor NAVLE questions, remember that PERINEAL URETHROSTOMY is the most cost-effective salvage procedure for feedlot steers but has HIGH STRICTURE RATES. TUBE CYSTOSTOMY is the procedure of choice for VALUABLE BREEDING ANIMALS as it allows time for stone dissolution while preserving breeding ability.

Procedure	Indication	Pros	Cons	Breeding Preserved?
Perineal Urethrostomy	Feedlot steers, salvage animals	Cost-effective, can perform standing	High stricture rate; reobstruction common	No
Penile Amputation with Low Urethrostomy	Feedlot steers for salvage slaughter	Simple, fast, allows continued growth before slaughter	Will stricture within 30 days; salvage only	No
Tube Cystostomy	Valuable animals, breeding bulls	Preserves breeding; allows stone dissolution; temporary	Catheter complications; 10-14 day hospitalization	Yes
Urethrotomy	Single stone at palpable location	Direct stone removal; may preserve breeding	Stricture risk; may need combined with cystostomy	Possibly
Bladder Marsupialization	Recurrent urolithiasis, pet animals	Permanent solution; shorter hospitalization	Urinary incontinence; urine scald; ascending pyelonephritis risk	No

Prevention

Due to the poor prognosis and expense associated with clinical urolithiasis, prevention is critical. Herd or flock implications must be addressed when a case is diagnosed.

Dietary Modifications

High-YieldCRITICAL for NAVLE: Ammonium chloride only prevents/dissolves STRUVITE (phosphatic) stones. It does NOT work for calcium carbonate stones and may INCREASE calcium stone formation by over-acidifying urine and increasing calcium excretion. Know the urolith type before recommending urinary acidification!

"WATER SALTS" for Prevention: W - Water availability (adequate, palatable, clean) A - Acidify urine (ammonium chloride for struvite only) T - Two to one calcium:phosphorus ratio E - Eliminate legume hay for males R - Roughage (increase forage, decrease concentrates) S - Salt supplementation (2-5%) A - Avoid high-phosphorus grains L - Limit magnesium (less than 0.6%) T - Trace minerals (adequate vitamin A) S - Silica pastures - restrict access for males

Prevention Strategy	Specific Recommendations
Calcium:Phosphorus Ratio	Maintain 2:1 to 2.5:1 ratio to prevent phosphatic stones; phosphorus should not exceed 0.6% of ration
Magnesium Restriction	Limit to 0.2-0.3% of ration (DM basis); never exceed 0.6%
Increase Forage	Promotes saliva production for phosphorus excretion; use grass hay, avoid legumes for males
Salt Supplementation	Add NaCl at 2-5% of ration to increase water intake and urine output
Urinary Acidification	Ammonium chloride 0.5-2% of ration; target urine pH less than 6.5; effective ONLY for struvite prevention
Water Availability	Provide adequate palatable water at appropriate temperatures; warm in winter, cool in summer
Avoid High-Risk Feeds	Do not feed horse grain to cattle; avoid alfalfa/legumes for males; monitor silica-rich pastures
Delay Castration	Delay until at least 6 months of age to allow urethral development (consider welfare implications)

Prognosis

Prognosis depends on duration of obstruction, presence of rupture, degree of azotemia, and treatment approach. Published success rates range from 35-95% depending on procedure and case selection.

Poor prognostic indicators: Bladder rupture, severe azotemia, obesity, poor clinical condition at presentation, elevated creatine kinase
Tube cystostomy: 80% success rate for restoring urethral patency in small ruminants; cattle data limited but similar expected
Perineal urethrostomy: 50% or more develop stricture or reobstruction within 12 months; salvage procedure only
Note: Salvage slaughter is NOT an option due to uremia affecting meat quality

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