28/10/2025
Fog Fever
Autumn grass has flourished this year following the dry spell. As a result, cattle have been grazed for longer during the Autumn period, but are we seeing a consequence to that?
We have heard reports of, and seen a couple of suspect Fog Fever cases in cattle (beef and dairy). This condition is medically known as Acute Bovine Pulmonary Oedema and Emphysema and triggered by a move to lush grass. Symptoms are typically observed 5-10 days after the move and may affect a group of animals, but their symptoms can vary greatly.
Mild cases often resolve spontaneously within a few days and include:
- Lethargy, but alert
- Increased breathing and heart rate (lungs sound clear)
Severely affected animals will have:
- Extreme respiratory distress (head stretched forward, tongue out and drooling)
- Relatively normal lung sounds and no coughing
- A loud grunt
- Emphysema (air under the skin, particularly over the back)
- A Normal temperature (despite the name!)
- Rapid improvement in a few days, or death.
The condition is caused by a sudden change from a low to a high protein diet, and high levels of the amino acid Tryptophan, found in fast growing, lush grass. Tryptophan is metabolised by the bugs in the rumen and converted into 3- methylindole, which is a toxic product that gets absorbs into the blood stream and actively damages the lung tissue.
Unfortunately there is no treatment for Fog Fever, apart from supportive therapy. Prevent animals from sudden exposure to lush grass by strip grazing / cutting / short grazing periods for at least 3 weeks and buffer with hay where necessary. Younger animals and sheep are much less susceptible so could be run ahead of adult cattle where grazing has run away.
