Bloat in Cattle

Bloat

• Bloat is an overdistension of the rumenoreticulum with gases of fermentation, either in the form of a persistent foam mixed with ruminal contents (primary or frothy bloat) or free gas separated from ingesta (secondary or free-gas bloat)
• Predominantly a disorder of cattle, but also seen in sheep
• Susceptibility to bloat varies and is genetically determined
• Death rates as high as 20% in cattle grazing bloat-prone pasture
• Economic loss from depressed milk production in non-fatal cases and from suboptimal use of bloat-prone pastures

Etiology and Pathogenesis

• Primary ruminal tympany (frothy bloat) caused by entrapment of normal gases of fermentation in a stable foam
• Coalescence of small gas bubbles inhibited, intraruminal pressure increases, and eructation cannot occur
• Factors influencing foam formation: soluble leaf proteins, saponins, hemicelluloses, salivary mucin, and chloroplast particles
• Bloat-producing pastures are rapidly digested, releasing small chloroplast particles that trap gas bubbles and prevent coalescence
• Protein content and rates of digestion and ruminal passage reflect the forage's potential for causing bloat
• Legume forages like alfalfa and clover have a higher percentage of protein and are digested more quickly, making them prone to bloat
• Other legumes like sainfoin, crown vetch, and fenugreek do not cause bloat due to condensed tannins that precipitate protein and are digested more slowly

Clinical Signs and Lesions

• In frothy bloat, the skin over the left flank becomes progressively more taut, and in severe cases, cannot be "tented"
• Dyspnea, grunting, mouth breathing, protrusion of the tongue, extension of the head, and frequent urination
• Rumen motility does not decrease until bloat is severe
• In secondary bloat, the excess gas is usually free on top of the solid and fluid ruminal contents
• Tympanic resonance over the dorsal abdomen left of the midline
• Free gas produces a higher pitched ping on percussion than frothy bloat
• Distension of the rumen can be detected on rectal examination
• Necropsy findings: congestion and hemorrhage of lymph nodes, epicardium, and upper respiratory tract, compressed lungs, and intrabronchial hemorrhage
• Cervical esophagus is congested and hemorrhagic, while the thoracic portion is pale and blanched (the "bloat line" of the esophagus)

Diagnosis and Treatment

• Clinical diagnosis of frothy bloat is usually obvious
• Emergency rumenotomy may be necessary in life-threatening cases
• Trocar and cannula can be used for emergency relief, but a larger bore instrument is necessary in peracute cases
• Antifoaming agents can be administered through the cannula or orally
• In frothy bloat, passing a stomach tube of the largest bore possible is recommended
• Various antifoaming agents are effective, including vegetable oils, mineral oils, and dioctyl sodium sulfosuccinate (docusate)

Control and Prevention

• Prevention of pasture bloat can be difficult
• Management practices to reduce risk of bloat: feeding hay before turning cattle on pasture, maintaining grass dominance in the sward, or using strip grazing to restrict intake
• Hay must constitute at least one-third of the diet to effectively reduce risk of bloat
• Continual administration of an antifoaming agent during the risk period is the most reliable method to prevent pasture bloat
• Antifoaming agents can be administered orally, sprayed onto the pasture, added to feed or water, or incorporated into feed blocks