Difference between revisions of "Category:Forestomach - Nutritional Pathology"

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.

Rumenal Acidosis

• Like bloat, rumenal acidosis is associated with mismanagement of feeding and involves cessation or depression of rumenal movements with development of a degree of tympany.
• More common in cattle and goats than in sheep due to differences in diet.

Clinical

• Animals display signs of abdominal discomfort, but usually recover if treated.
• Acute disease can result in death if acidosis is severe.

Pathogenesis

• Occurs following feeding of highly fermentable material, usually carbohydrate, in the form of concentrate or cereal
  • e.g. in barley beef feeding systems.
• An overgrowth of Gram positive bacteria results, breaking carbohydrate down very quickly.
  • Increased volatile fatty acid production decreases the rumen pH to about 5.
    • Rumen epithelium is damaged- ruminitis.
    • Osmotic effects of rumen contents produce severe dehydration.
    • Death may ensue when the rumen pH drops to 4.5 or below.
• Normal flora may invade the damaged wall of rumen e.g. Fusiformis necrophorum.
  • Results in areas with mushy necrotic papillae.
  • Especially on pillars and ventral parts of rumen.
• Excess gas production may occur
  • Concentrate does not contain soluble proteins, therefore foam does not develop.
  • Only mild to moderate free gas bloat is likely- much of the rumenal distension which occurs with rumenal acidosis is due to fluid sequestration in the rumen.

Pathology

Gross

• Gross PM findings may be non-specific.
• Ruminal stasis/bloat leads to rumen distension
• Rumen contents are porridge-like.
• Rumenitis may be present
  • Normal flora invading wall of rumen may enter blood as thromboemboli and travel in the portal flow to liver
  • Focal abscesses are produced, which heal with sunken star-shaped scars.
• Overgrowth of Clostridia may cause endotoxic shock with widespread petechial haemorrhages.

Histological

• Microvesicles may be present in the epithelium of the rumen papillae.
  • Contain mainly neutrophils
• May be focal erosions/ulceration.

Sequelae

• Scarring- necrotised papillae are replaced by smooth epithelium closely adherent to sub mucosa.
• Has economic significance since many barley beef livers are condemned at meat inspection.
• More persistent organisms can invade rumen wall producing chronic infection.
  • These are often fungi, e.g. Mucor (see Mucormycosis).