Bloat

Bloat/Tympany

• When eructation fails, the rumen becomes distended due to the accumulation of gas produced by the fermentation process. This distension is known as bloat or tympany.

Clinical

• The disease is acute and progressive and will result in death in a matter of hours.

Pathology

• In severe bloating, that the rumen almost fills the abdomen.
  • Diaphragm is displaced forwards, compressing the lungs.
  • Posterior vena cava (lying dorsally) is also compressed, reducing the venous return to the heart.
  • Respiration is depressed and animals die from anoxia.
    

    Oesophageal "bloat line" (Courtesy of Elspeth Milne)
    • Blood is dark (hypoxic) and clots poorly.
• The anterior parts of the body are often characteristically acutely congested.
  • Oedema and subcutaneous haemorrhage of head and neck tissues.
  • Oesophageal "bloat line" at thoracic inlet.
    • Congested and haemorrhagic cranially, pale caudally.

Pathogenesis

• There are two forms of bloat:
  • Frothy bloat/ Primary bloat
    • Occurs following ingestion of large amounts of succulent green plant material. This is highly fermentable and produces large amounts of gas.
    • Material contains high levels of soluble proteins. These act as foaming agents by reducing surface tension but increasing surface viscosity of rumenal liquids and a stable rumenal foam forms.
    • The volatile fatty acids of the plant material consumed lower pH, optimising conditions for formation of froth.
    • Gas present in bubble form is insufficient to trigger eructation, and so the rumen becomes distended.
  • Free gas bloat/ Secondary bloat
    • May be:
      • Acute
        • Due to sudden oesophageal obstruction, for example by a solid foreign body (e.g. a piece of potato or turnip).
      • Chronic
        • Results from partial oesophageal obstruction/ compression, or from interference with the normal eructation mechanism, e.g. with:
          • partially obstructive foreign bodies
          • actinobacillosis in the oesophagus or oesophageal groove
          • oesophagus or groove tumours
          • chronic inflammatory or adhesive disease of the reticulum
        • Some passage of gas is possible, so gas build-up and distenesion is more prolonged.
        • Interference with cardiac and respiratory function is seldom life threatening.