Fog fever

Fog fever, also known as acute bovine pulmonary edema and emphysema (ABPEE), is a non-infectious respiratory disease that primarily affects mature cattle, typically those over two years old. It is characterized by sudden onset of severe respiratory distress, often leading to death.

Etiology:

The primary cause of fog fever is the ingestion of lush pastures, particularly those containing high levels of L-tryptophan. L-tryptophan is converted in the rumen to 3-methylindole (3-MI), a pneumotoxic compound. When absorbed into the bloodstream, 3-MI is metabolized in the lungs to a toxic metabolite that damages type I alveolar cells, leading to pulmonary edema and emphysema.

Risk Factors:

Several factors increase the risk of fog fever:

• Sudden pasture change: Moving cattle from dry, sparse pastures to lush, rapidly growing pastures.
• Pasture type: Pastures high in L-tryptophan, such as those dominated by brassicas (e.g., rape, kale) or certain weeds.
• Cattle age and breed: Mature cattle are more susceptible than young cattle. Breed predisposition is not well-established.
• Weather: Foggy or humid conditions may contribute to the problem, possibly by affecting pasture growth and composition.

Clinical Signs:

Affected cattle typically exhibit the following symptoms:

• Sudden onset of labored breathing
• Rapid, shallow respirations
• Frothing at the mouth
• Anxiety and distress
• Extension of the head and neck
• Open-mouth breathing
• Crackles and wheezes on lung auscultation
• Death, often within hours of the onset of clinical signs

Diagnosis:

Diagnosis is typically based on clinical signs, history of recent pasture change, and post-mortem examination. Lung lesions, including edema, emphysema, and hyaline membrane formation, are characteristic findings.

Treatment:

Treatment is often unrewarding due to the rapid progression of the disease. Options include:

• Moving affected cattle to drylot or a different pasture.
• Administration of diuretics to reduce pulmonary edema.
• Administration of corticosteroids to reduce inflammation.
• Supportive care, such as oxygen therapy.
• Minimize stress to avoid further exacerbation of the condition.

Prevention:

Preventive measures are crucial to minimize the risk of fog fever:

• Gradual introduction to lush pastures.
• Supplementation with hay or other dry forage during pasture transitions.
• Avoidance of pastures known to be high in L-tryptophan.
• Monitoring cattle closely for signs of respiratory distress after pasture changes.
• Consideration of ionophore supplementation, which may reduce 3-MI production in the rumen.

Prognosis:

The prognosis for cattle affected with fog fever is generally poor, with a high mortality rate. Early detection and prompt treatment may improve the chances of survival.