Bovine Bloat and Choke Study Guide

Overview and Clinical Importance

Ruminal tympany (bloat) and esophageal obstruction (choke) are critical gastrointestinal emergencies in cattle that require rapid recognition and intervention. Bloat is an overdistension of the rumenoreticulum with fermentation gases, while choke refers to obstruction of the esophagus by foreign bodies or feed material. Both conditions can be rapidly fatal if untreated and represent significant causes of sudden death in beef and dairy operations. These topics are high-yield for the NAVLE due to their clinical prevalence and the need for immediate, decisive treatment.

Ruminal Tympany (Bloat)

Bloat is defined as overdistension of the rumenoreticulum with gases of fermentation. It is predominantly a disorder of cattle but can also occur in sheep and goats. The condition occurs when the normal eructation mechanism is impaired, leading to accumulation of carbon dioxide and methane in the rumen. Annual mortality rates from bloat can approach 1% in dairy cattle and up to 20% in severe pasture bloat outbreaks.

Classification of Bloat

Pathophysiology

Normal Eructation Mechanism

Under normal conditions, ruminants produce 30-50 liters of gas per hour through microbial fermentation. This gas (primarily CO2 and methane) rises to the dorsal gas cap in the rumen and is expelled through eructation (belching). The eructation reflex requires: (1) stimulation of tension receptors in the reticular wall by gas, (2) relaxation of the cardia, and (3) coordinated rumen contractions to move gas toward the cardia. Cattle normally eructate 15-20 times per hour.

Primary (Frothy) Bloat - Pasture Bloat

Occurs when cattle graze lush, immature leguminous pastures (alfalfa, clover, Lucerne) in the vegetative or pre-bloom stage. These highly digestible plants release soluble proteins (leaf proteins) that become denatured and form stable foam that traps fermentation gases. The foam prevents gas bubbles from coalescing into a large gas cap that can stimulate the eructation reflex. Reduced saliva production from succulent pastures (less chewing required) decreases the buffering capacity and increases foam stability.

Primary (Frothy) Bloat - Feedlot Bloat

Occurs in cattle fed high-concentrate (grain) diets, typically after 1-2 months on feed. Streptococcus bovis and other bacteria proliferate on rapidly fermentable carbohydrates and produce exopolysaccharides (mucopolysaccharide slime) that stabilizes foam. Finely ground grain (particle size less than 388 micrometers) exacerbates the problem by providing fine particles that further stabilize foam.

Secondary (Free-Gas) Bloat

Results from physical obstruction of eructation or neurological impairment of the eructation reflex. Causes include esophageal obstruction (choke), vagal nerve damage (hardware disease, chronic pneumonia, pleuritis), tetanus, botulism, hypocalcemia (milk fever), ruminal acidosis with atony, and positional factors (lateral recumbency, cast animals).

Clinical Signs

Diagnosis

Clinical diagnosis is typically straightforward based on history and physical examination findings. Key diagnostic steps include: (1) Visual inspection - distension of the left paralumbar fossa; (2) Percussion - tympanic resonance (ping) in free-gas bloat vs. dull sound in frothy bloat; (3) Passage of orogastric tube - diagnostic and therapeutic; determines bloat type based on gas release; (4) Rectal examination - rumen distension palpable; (5) History - recent access to legume pastures, grain diets, or underlying conditions.

Treatment

Prevention Strategies

Pasture Bloat Prevention

• Use grass-legume mixed pastures (aim for less than 50% legume content)
• Feed hay before turning cattle onto bloat-prone pastures
• Avoid grazing when pastures are wet with dew or after rain
• Turn cattle out when forages are more mature (post-bloom)
• Administer poloxalene prophylactically (10-20 g/head/day in feed, water, or molasses blocks)
• Consider sainfoin or birdsfoot trefoil (high-tannin legumes that do not cause bloat)
• Use strip grazing with daily poloxalene application to pasture

Feedlot Bloat Prevention

• Include 10-15% roughage in the diet (cereal straw, grass hay)
• Use rolled or cracked grain rather than finely ground grain
• Avoid pelleted rations made from finely ground grain
• Include ionophores (monensin) in the ration
• Gradual dietary adaptation over 2-3 weeks when transitioning to high-grain diets
• Consistent feed calling, mixing, and delivery to avoid intake variation

Esophageal Obstruction (Choke)

Choke is obstruction of the esophagus, most commonly by feedstuffs or foreign bodies. It is the most common esophageal disease in cattle and represents a veterinary emergency because complete obstruction prevents eructation and leads to rapidly fatal secondary (free-gas) bloat. Cattle characteristically obstruct on single, solid objects that are swallowed without adequate mastication.

Etiology

Common Obstructing Objects

• Apples, potatoes, turnips, beets, swedes
• Ears of corn, cornstalks, kiwifruit
• Medicated boluses (administered incorrectly)
• Trichobezoars (hairballs)
• Foreign bodies (feeding tubes, wire, plastic)

Common Obstruction Sites

• Cervical esophagus (most common; can be palpated externally)
• Thoracic inlet
• Base of the heart
• Cardia (entrance to rumen)

Clinical Signs of Choke

Diagnosis of Choke

• History and clinical signs: Recent access to root vegetables, apples, or foreign objects; characteristic signs of ptyalism and bloat
• External palpation: Cervical obstructions often palpable on the left side of the neck
• Oral examination: Rule out oral/pharyngeal foreign bodies (first rule out rabies in endemic areas!)
• Passage of stomach tube: Tube cannot pass beyond the obstruction; confirms location
• Radiography: Double-contrast radiography (barium + air) can localize obstruction and assess esophageal integrity
• Endoscopy: When available, confirms diagnosis and may allow removal of certain foreign bodies

Treatment of Choke

Step 1: Address Secondary Bloat First

If bloat is life-threatening, decompress the rumen BEFORE attempting to relieve the obstruction. Use a trocar/cannula or needle inserted into the left paralumbar fossa to release gas. This stabilizes the patient for further treatment.

Step 2: Conservative Management

• Withhold feed and water to prevent aspiration and further obstruction
• Sedation with xylazine (0.05 mg/kg IM) or acepromazine (0.05-0.1 mg/kg IV/IM) relaxes esophageal smooth muscle
• Smooth muscle relaxants (hyoscine-n-butylbromide) may aid passage
• Small volumes of lubricant (paraffin oil) per os
• Wait 3-6 hours for object to macerate and pass spontaneously (especially with feed pellets)

Step 3: Active Removal

• External massage: For cervical obstructions; gently massage object upward toward oral cavity for retrieval
• Probang/stomach tube: Gentle pressure may push object into rumen (preferred for smooth objects like potatoes)
• Lavage: Water delivered via stomach tube to soften and break up obstruction
• Endoscopic retrieval: When available; allows visualization and removal of foreign bodies

Step 4: Surgical Intervention

• Esophagotomy: Surgical incision into esophagus to remove foreign body; indicated when other methods fail; cervical approach preferred
• Rumenotomy: Access rumen surgically; retrieve object from the cardia; useful when object is near rumen entrance
• Two-layer closure: Esophagus sutured in two layers (mucosa/submucosa + muscular layer); longitudinal incision preferred

Complications of Choke

• Aspiration pneumonia: Risk from regurgitated material; especially chronic cases
• Esophageal stricture: Circumferential mucosal damage from prolonged contact (greater than 24 hours) leads to scarring and narrowing
• Esophageal rupture: Often fatal complication of chronic obstruction or aggressive manipulation
• Esophageal necrosis: Pressure necrosis from prolonged contact with foreign body
• Surgical complications: Wound dehiscence, periesophageal cellulitis (esophagus lacks a serosal layer)

Prognosis

Bloat: Good to excellent if treated promptly. Once recumbent, prognosis becomes grave. Recovery after treatment is usually uneventful.

Choke: Good for uncomplicated cases treated within hours. Prognosis worsens significantly with duration greater than 24 hours, development of complications (stricture, rupture, aspiration pneumonia), or need for surgical intervention.