Bloat and Choke in Cattle: A Comprehensive NAVLE Study Guide

Overview
Bloat (ruminal tympany) is a condition characterized by the excessive accumulation of gas in the rumen, leading to distension and potential respiratory distress. It is classified into two types:
Primary (Frothy) Bloat: Gas is trapped in a stable foam, often associated with diets high in legumes or finely ground grains (Merck Veterinary Manual, Bivatec)
Secondary (Free-Gas) Bloat: Gas accumulates due to physical obstruction or impaired eructation mechanisms (NRCS, Vetscraft).

Frothy Bloat in Cattle

Classic Presentation

• Acute abdominal distention, primarily on the left side
• Tachycardia
• Open-mouthed breathing
• Frothy, green, stable rumen ingesta:
  • Foam with tiny, persistent bubbles that do not pop
• Inability to eructate (belch) → trapped gas
• May be found acutely dead with left-sided distention

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Etiology / Risk Factors

• Pasture-associated bloat:
  • Cows recently introduced to legume pastures (within last 2 weeks)
  • Common legumes: alfalfa, clover
• Feedlot bloat:
  • Exact cause unclear
  • Possible factors:
    • Slime-producing rumen bacteria
    • Finely ground, highly fermentable feed particles
• Free gas bloat (differential):
  • Due to obstruction of normal eructation pathway (e.g., choke, positional changes)

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Diagnosis

• Visual Observation:
  • Obvious bloating—distention more on left flank
• Differentiate Frothy vs. Free Gas Bloat:
  • Pass a stomach tube:
    • Frothy Bloat:
      • Small amount of frothy green rumen contents oozes out
      • No significant gas release or relief
    • Free Gas Bloat:
      • Large volume of gas released
      • Immediate relief of distention

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Treatment

Mild / Early Cases

• Antifoaming Agents:
  • Vegetable or mineral oil: 250–500 mL
  • Dioctyl sodium sulfosuccinate (DSS): often combined with oil
  • Poloxalene:
    • Effective for pasture (legume) bloat
    • Not effective for feedlot bloat

Severe / Life-Threatening Cases

• Emergency Procedures:
  • Rumenotomy (surgical intervention)
  • Large-bore trocar or rumen cannula (2.5 cm diameter)
    • Allows gas release over hours
    • Administer antifoaming agents through the trocar or cannula

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Key Points

Prognosis

• Good if recognized and treated early
• Poor outcome if animal found dead or if respiratory distress is prolonged

Prevention

• Pasture (Legume) Bloat:
  • Ionophores (e.g., monensin, lasalocid)
  • Gradual introduction to lush pastures
  • Feed hay before pasture access to limit sudden fermentation
• Feedlot Bloat:
  • Incorporate 10–15% coarse-chopped roughage into the diet
  • Use ionophores (e.g., lasalocid) as feed additives

Causes
Primary Bloat: Ingestion of lush legume pastures (e.g., alfalfa, clover), high-concentrate diets, or finely ground grains (Nebraska Extension, Ag & Natural Resources College)
Secondary Bloat: Esophageal obstruction (choke), hypocalcemia, vagal indigestion (PMC, Merck Veterinary Manual)

Clinical Signs

• Distension of the left paralumbar fossa (Ag & Natural Resources College)
• Discomfort, restlessness, vocalization (Bivatec)
• Dyspnea and open-mouth breathing
• Sudden death in severe cases (Wikipedia)

Diagnosis

• Clinical examination revealing ruminal distension
• Passing a stomach tube to differentiate between frothy and free-gas bloat (Merck Veterinary Manual)

Treatment
Frothy Bloat: Administration of antifoaming agents such as poloxalene via stomach tube (The Cattle Site)
Free-Gas Bloat: Relief via stomach tube or trocarization in emergencies (Bovine Veterinarian)
Emergency rumenotomy may be required in severe cases (Merck Veterinary Manual)

Prevention

• Gradual introduction to high-risk pastures
• Feeding dry hay before turnout
• Use of bloat-preventive feed additives (Nebraska Extension)

Choke in Cattle

Overview
Choke is esophageal obstruction caused by the ingestion of large food items or foreign bodies. It is a veterinary emergency due to the high risk of secondary bloat (CowDVM)

Causes

• Ingestion of large root vegetables, fruits, or poorly chewed feed
• Foreign bodies such as plastic, cloth (Merck Veterinary Manual)

Clinical Signs

• Excessive salivation and coughing (CowDVM)
• Repeated attempts to swallow (Texas Parks & Wildlife)
• Distension of the left paralumbar fossa due to secondary bloat (Ag & Natural Resources College)

Diagnosis

• History and clinical signs (CowDVM)
• Palpation of the esophagus
• Endoscopy or radiography if available (Merck Veterinary Manual)

Treatment

• Sedation and manual removal if the object is palpable
• Use of a stomach tube or probang to dislodge the obstruction (The Cattle Site)
• Surgical intervention (esophagotomy) in refractory cases

Prevention

• Proper feed processing to avoid large particles
• Avoid feeding large root vegetables or fruits whole

NAVLE-Style Multiple-Choice Questions

Question 1: Diagnosis
Clinical Scenario:
A 3-year-old beef cow presents with sudden onset of left-sided abdominal distension, discomfort, and dyspnea after grazing on lush clover pasture.

Question:
What is the most likely diagnosis?

A. Traumatic reticuloperitonitis
B. Primary (frothy) bloat
C. Secondary (free-gas) bloat
D. Choke
E. Left displaced abomasum

Correct Answer: B. Primary (frothy) bloat
Explanation: The sudden onset after grazing on legume-rich pasture suggests frothy bloat, characterized by stable foam formation in the rumen. (Bovine Veterinarian, Wikipedia)

Question 2: Treatment
Clinical Scenario:
A cow exhibits signs of bloat. A stomach tube is passed, and gas is released, relieving the distension.

Question:
What type of bloat is most consistent with this response?

A. Primary (frothy) bloat
B. Secondary (free-gas) bloat
C. Vagal indigestion
D. Choke
E. Abomasal impaction

Correct Answer: B. Secondary (free-gas) bloat
Explanation: Relief of bloat by stomach tube indicates free-gas bloat, where gas accumulates due to impaired eructation (Merck Veterinary Manual)

Question 3: Complication
Clinical Scenario:
A cow with esophageal obstruction is not treated promptly.

Question:
What is the most likely life-threatening complication?

A. Aspiration pneumonia
B. Secondary (free-gas) bloat
C. Esophageal stricture
D. Ruminal acidosis
E. Peritonitis

Correct Answer: B. Secondary (free-gas) bloat
Explanation: Esophageal obstruction prevents eructation, leading to gas accumulation and potentially fatal ruminal tympany (Merck Veterinary Manual)