Author: Elizabeth Brock

Parelaphostrongylus tenuis (the “meningeal worm”) resides in white-tailed deer without causing clinical disease but is the catalyst for devastating neurologic disease in camelids, and sometimes in sheep and goats as aberrant hosts. If you practice where deer and camelids co-exist, monitor closely for signs like hindlimb weakness and ataxia.

Who Gets Sick (and Who Doesn’t)

Deer are asymptomatic carriers, whereas llamas, alpacas, and small ruminants develop progressive neurologic signs after infection. Seasonality follows intermediate host (gastropod) activity, but cases can appear whenever an animal encounters infective larvae.

Clinical Signs to Know

Expect a number of neurological deficits, including:

• Ataxia
• Pelvic limb weakness
• Circling
• Stiffness or lameness
• Scoliosis (occasionally)

Animals may appear to improve temporarily after anti-inflammatory therapy, misleading owners, but clinical deterioration often resumes.

Diagnosis by Clinical Sign Recognition

No simple ante-mortem test or gold-standard treatment exists for P. tenuis. Clinicians diagnose the disease by recognizing characteristics and clinical signs and confirming findings with CSF when feasible. During necropsy, collect biopsies to confirm infection.

The absence of fever can help distinguish P. tenuis from listeriosis, but clinical overlap occurs. Rely on pattern recognition and pragmatic testing to guide your diagnosis.

Treatment Realities

There’s no definitive, universally effective treatment regimen. Clinicians typically use anthelmintics such as fenbendazole or ivermectin but must stay alert for resistance issues. Combine anthelmintics with anti-inflammatories, attentive nursing care, and physical support. Prepare owners for a guarded prognosis, especially if animals become recumbent.

In-Field Prevention

• Exclude deer: build sturdy fencing at least 9-10 feet high to prevent deer access
• Strategic deworming: use targeted anthelmintic protocols during at-risk seasons (every 30-45 days from spring to fall, tailored to avoid resistance) while following local guidance
• Pasture management: drain standing water, control vegetation, and rotate grazing areas to reduce gastropod vectors

Prevention is Key

With Parelaphostrongylus tenuis, clinicians cannot rely on a definitive test or standardized treatment protocol. That reality makes prevention the most powerful intervention. Focus on reducing exposure through effective deer exclusion, thoughtful pasture and gastropod control, and strategic, resistance-conscious deworming plans. Clear owner education about environmental risk and early neurologic changes helps set realistic expectations and supports earlier intervention when cases arise.

More from Zuku Learning

• Master more NAVLE^® concepts
• Subscribe to the Question of the Day to receive a NAVLE^® question delivered to your inbox daily
• Review the No Zebras: How to Triage your NAVLE^® Study for Maximum Points blog
• Review the How to Triage your NAVLE^® Study for Maximum Points blog

When a fresh dairy cow goes off feed and milk production drops, your diagnostic radar should light up. One of the most common culprits behind these signs? A displaced abomasum (DA), a condition that every veterinary student should master for both clinical practice and NAVLE^® success.

What Is a Displaced Abomasum?

The abomasum is the glandular, true stomach in ruminants. In healthy cows, it sits on the ventral midline of the abdomen, slightly right of center. But during early lactation, especially in cows experiencing postpartum complications, it can become distended with gas and “float” out of position. This can result in a left displaced abomasum (LDA) or, more critically, a right displaced abomasum (RDA), which can escalate to abomasal volvulus.

LDAs are more common and often stable. RDAs, on the other hand, are surgical emergencies because they may compromise blood flow. 

Clinical Signs and Common Presentations

There’s a classic pattern to DA cases that you’ll hear time and again:

• Fresh cow (within 4 weeks of calving)
• Off feed
• Down in milk production

If you hear an audible “ping” during percussion between the left elbow and the tuber coxae, you’ve got a strong case for LDA.

Other possible signs include:

• Decreased rumen contractions
• Caudal ribs on left, in front of paralumber fossa pushed outward by LDA (“sprung”)
• Mild dehydration
• Changes in manure output (scant or liquid)
• Tachycardia and colic behaviors in volvulus cases

Key Diagnostic Tools

While clinical signs often point the way, these tools help confirm the diagnosis:

• Auscultation & percussion: A high-pitched ping over ribs 9–13 on the left side = LDA
• Bloodwork: Common findings include hypochloremia, hypokalemia, and mild metabolic alkalosis
• Ketone testing: Increased blood or urine ketone levels suggests concurrent ketosis (either primary or secondary)
• Rectal palpation: RDAs or volvulus may be palpable; LDAs generally are not
• Liptak test: Rarely used, but abomasal fluid tapped near the ping is acidic (pH ~2)

Treatment Options and When to Use Them

Treatment depends on severity, cow value, and available resources. 

Medical Management (LDA only):

• Roll the cow (right → back → left) to reposition the abomasum: RECURRENCE LIKELY
• Administer oral propylene glycol for ketosis
• Provide IV or oral calcium if suspect hypocalcemia
• Feed palatable, high-quality forage
• Optional: rumen transfaunation from a healthy cow

Surgical Management (LDA, RDA, volvulus):

• LDA ONLY: Roll and toggle/tack (blind procedures; more common than the two below) 
• Standing right flank omentopexy
• Ventral abomasopexy (more anatomically correct but requires cow to be in dorsal recumbency)

As a rule of thumb: “Never let the sun set on an RDA.” RDAs and volvulus are emergencies and require immediate intervention. 

Prognosis and Prevention Tips

Prognosis is excellent for simple LDAs, moderate for RDAs, and poor for abomasal volvulus, especially with high heart rates or prolonged illness. 

To reduce incidence:

• Balance prepartum nutrition to prevent negative energy balance
• Monitor fresh cows closely for other periparturient diseases
• Maintain excellent record-keeping and target <1% DA incidence in the herd

DA Management = Pattern + Practice

Whether you’re in the clinic or prepping for NAVLE^®, remember: DA cases reward pattern recognition. Recognize the triad of a classic presentation. Know your ping locations. Match your treatment plan to the cow in front of you.

More from Zuku Learning:

• Master NAVLE^® concepts
• Subscribe to the Question of the Day to receive a NAVLE^® question delivered to your inbox daily
• Review the LDA vs. RDA in Dairy Cows: Key Differences Every Vet Student Must Know blog
• Review the Ketosis in Fresh Dairy Cows: Causes, Diagnosis, and How to Treat It blog

When a high-producing dairy cow gives birth to a calf, her energy demands surge, and her appetite often can’t keep up. The result? Negative energy balance and a condition every veterinary student must know cold: bovine ketosis.

Whether primary or secondary, ketosis is more than a metabolic footnote. Left unchecked, it can lead to displaced abomasum (DA), immune suppression, and decreased fertility.

Let’s break down how to catch it early, treat it effectively, and prevent it from tanking your herd’s productivity or your NAVLE^® score.

What Is Bovine Ketosis?

Ketosis occurs when cows, especially in the first 3 to 6 weeks postpartum, mobilize fat faster than the liver can convert it into usable glucose. This overflow produces ketone bodies (like beta-hydroxybutyrate, or BHB) that accumulate in the blood and urine.

There are 2 key types:

• Primary ketosis: Driven by poor feed intake or high milk output
• Secondary ketosis: Triggered by another disease that suppresses appetite, like metritis or left-displaced abomasum (LDA)

Risk is highest in:

• Over-conditioned cows at calving 
• Multiparous cows 
• Herds with poor transition nutrition

Clinical Signs to Watch For

Unlike obvious, acutely sick animals, cows with clinical ketosis often initially fly under the radar.

Common clinical signs include:

• Dull or lethargic demeanor 
• Reduced dry matter intake 
• Drop in milk production 
• Mild dehydration 
• “Sweet” or acetone-like breath (in advanced cases)

In a classic case, a recently fresh cow with ketosis can show these clinical signs, all of which may also precede the diagnosis of other problems, like LDA, for example. Test blood BHB on every cow with this pattern of signs to avoid missing cases.

Bottom line: ketosis might not shout, but it whispers persistently. Tune into the pattern.

Diagnosing Ketosis in Cows

Early diagnosis is critical to prevent complications. Two primary tools:

1. Blood BHB meter
   • Normal: <1.2 mmol/L 
   • Subclinical ketosis: 1.2–3.0 mmol/L 
   • Clinical ketosis: >3.0 mmol/L
2. Urine ketone test strips
   • Fast, affordable, but less precise than blood

Also assess:

• Appetite and rumen activity 
• Signs of concurrent conditions (e.g., DA, metritis) 
• Bloodwork for hypocalcemia, hypokalemia, and alkalosis, which often coexist

Treatment and Nutritional Support for Ketosis

Once diagnosed, early intervention can turn things around fast.

Key treatment components:

• Oral propylene glycol (300–500 mL daily for 3–5 days): provides a glucose precursor for liver metabolism 
• Calcium supplementation: oral or subQ calcium is typically warranted, and, if there is clear evidence of  hypocalcemia (especially in sluggish or cold cows), give slow IV calcium borogluconate 
• Potassium support: use KCl boluses or drenches for cows off feed (they quickly become hypokalemic) 
• Access to high quality, palatable forage

Prevention Through Nutrition and Monitoring

Preventing clinical ketosis begins before calving.

Dry cow nutrition goals:

• Avoid over-conditioning
• Balance dietary cation-anion difference (DCAD)
• Promote consistent feed intake

Transition strategies:

• Introduce lactation diets gradually
• Monitor cows using wearable rumination technology
• Keep detailed records to spot patterns and intervene early

If more than 15–20% of fresh cows are testing positive for subclinical ketosis, it is time to audit the herd’s transition protocols.

Tune Into the Subtle Signs

Ketosis isn’t always obvious. But vet students and new grads who learn to recognize its early signs, especially when paired with post-partum risks (e.g., LDA, retained placenta, metritis, mastitis), will be miles ahead in both herd management and boards prep.

Remember:

• Know the risk windows
• Use cow-side diagnostics
• Treat early and proactively
• Be proactive with nutrition

More from Zuku Learning

• Master NAVLE^® concepts
• Subscribe to the Question of the Day to receive a NAVLE^® question delivered to your inbox daily
• Review the Displaced Abomasum in Dairy Cows: A Complete Guide for Vet Students blog
• Review the LDA vs. RDA in Dairy Cows: Key Differences Every Vet Student Must Know blog

Displaced abomasum is one of the most NAVLE^®-tested conditions in dairy practice, and for good reason. It is common, clinically relevant, and a perfect case for diagnostic reasoning.

But not all displacements are created equal.

Understanding the key differences between left displaced abomasum (LDA) and right displaced abomasum (RDA) can help you respond appropriately in the field and choose the right answer under pressure.

What Is a Displaced Abomasum?

The abomasum is the cow’s true stomach, normally positioned on the ventral midline of the abdomen, slightly right of center. Displacement happens when gas accumulates, causing the abomasum to “float” out of place.

This usually occurs in the first month postpartum, especially in cows with other issues like:

• Metritis 
• Retained placenta 
• Ketosis 
• Hypocalcemia

Why? All of these reduce feed intake and rumen fill, increasing gas buildup and disrupting motility.

LDA vs. RDA: What’s the Difference?

In an RDA, the abomasum has space to twist on its axis, much like gastric dilatation/volvulus (GDV) in dogs, cutting off blood supply and leading to shock or death if untreated.

Clinical Signs: Left vs. Right DA

Shared signs:

• Off feed 
• Drop in milk production 
• Reduced rumen contractions 
• “Ping” on percussion 
• Recent calving history (often, but not required)

RDA/Volvulus-specific red flags:

• Tachycardia (HR > 100 bpm) 
• Colic-like behavior (restless, kicking at belly) 
• Severe dehydration 
• “Papple” shape to abdomen (left side = apple, right side = pear) 
• Rapid deterioration

The degree of tachycardia is proportional to prognosis: the faster the heart rate, the worse the outlook.

Diagnostic Clues That Help You Tell Them Apart

LDA ping:

• Location: ribs 9-13 on the left, along a line between elbow and tuber coxae 
• Accompanied by history of gradual decline, +/- ketosis

RDA ping:

• More caudal and ventral on the right side 
• May extend to 9th rib space 
• Often accompanied by distended abdomen and altered rectal findings

Volvulus-specific signs:

• Severe colic 
• Decreased or absent manure 
• Metabolic alkalosis with hypochloremia and hypokalemia 
• Distended abomasum on rectal palpation in right cranial abdomen

Treatment and Prognosis: When to Act Fast

LDA can be managed medically first, with an omentopexy or toggle if relapse occurs:

• Sedation + rolling (recurrence is likely!) 
• Oral calcium and propylene glycol 
• High-quality forage 
• Rumen transfaunation

RDA or volvulus, on the other hand, always requires:

• Immediate surgical correction
• Right flank omentopexy or abomasopexy
• Possible fluid and electrolyte support

NAVLE^® Tip:

Only LDAs are eligible for roll-and-toggle procedures. Blind tack surgeries are dangerous in RDAs due to risk of torsion or misplacement.

Summary Table: LDA vs. RDA Cheat Sheet

Recognize the Pattern, Respond with Confidence

Whether you are palpating in the field or selecting answers in a timed test, the key to success with displaced abomasum is pattern recognition:

• Fresh cow 
• Off feed, down in milk 
• Ping → determine side and urgency 
• Tachycardia or colic? → think volvulus 
• Move quickly, treat confidently

As the old saying goes: “Never let the sun set on an RDA.”

More from Zuku Learning:

• Master NAVLE^® concepts
• Subscribe to the Question of the Day to receive a NAVLE^® question delivered to your inbox daily
• Review the Displaced Abomasum in Dairy Cows: A Complete Guide for Vet Students blog
• Review the Ketosis in Fresh Dairy Cows: Causes, Diagnosis, and How to Treat It blog