Bloat

Description

Bloat is the ruminal distension caused by excessive accumulation of gas produced by the fermentation process. Bloat can be categorised according to cause into Primary bloat (frothy bloat) and secondary bloat (free gas 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.

Seconday bloat

Secondary bloat or free gas bloat results from any condition that causes oesophageal obstruction or interferes with eructation.

• • • • 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.

References

• Andrews, A.H, Blowey, R.W, Boyd, H and Eddy, R.G. (2004) Bovine Medicine (Second edition), Blackwell Publishing
• Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial

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.

Also known as:

Ruminal tympany