Fog fever, a rapid-onset respiratory disease in cattle, is most commonly associated with sudden forage changes during the grazing season. In a recent Cattle Chat podcast episode, K-State beef cattle experts discussed how producers can recognize risk factors early and implement management strategies to reduce losses due to fog fever.
Also known as acute bovine pulmonary emphysema and edema (ABPEE), fog fever typically affects adult cattle within days of being moved from dry or low-quality forage to lush, high-protein pastures — particularly in the spring and fall.
The sudden dietary change triggers bacterial production of a compound that damages lung tissue, leading to severe breathing difficulties, frothing at the mouth, anxiety, and, in many cases, death. The experts suggested there is no specific cure once clinical signs develop, placing emphasis on prevention.
“Understanding how cattle adapt to forage changes is key,” says K-State toxicologist Todd Gunderson. “If producers gradually introduce cattle to lush pasture — starting with only a few hours of access per day — it gives the rumen microbes time to adjust, which can significantly reduce the risk of fog fever.”
Experts also highlighted nutritional practices that help support rumen adaptation prior to turnout.
“Feeding quality dry hay for several days before grazing lush growth gives cattle a fuller rumen and slows the abrupt shift in diet that often triggers fog fever,” Gunderson says.
Prevention suggestions from the team include:
- Introduce lush forage gradually.
Begin with limited grazing hours and increase exposure over 10–14 days to allow rumen microbes to adapt. - Provide dry hay ahead of turnout.
A full rumen at pasture entry helps prevent overeating high-protein grasses that can lead to toxin formation. - Consider ionophores when appropriate.
Technologies such as monensin can moderate ruminal fermentation patterns, potentially lowering risk during transitions, but should be used in consultation with a veterinarian. - Manage pasture timing.
Delaying grazing of lush regrowth until after frost or cutting it for hay first can lessen exposure to high tryptophan levels.
Fog fever’s rapid onset and high mortality rate mean producers must be proactive. Although there is no proven effective treatment once severe signs develop, careful management strategies can drastically reduce the likelihood of outbreaks.
