Acute Bovine Pulmonary Emphysema and Edema in Ox: Fog Fever Signs & Care
- See your vet immediately. Fog fever can cause sudden, severe breathing distress or death in adult cattle after a recent move onto lush pasture.
- This condition usually appears 5 to 10 days after cattle are turned onto better, rapidly growing pasture, especially in late summer or fall.
- Common signs include fast breathing, open-mouth breathing, an extended neck, drooling, an expiratory grunt, and worsening distress with exercise or handling.
- There is no reliably effective treatment once severe signs start, so calm handling, minimizing movement, and herd-level management are central parts of care.
- Prevention often focuses on gradual pasture introduction, feeding hay before turnout, limiting early grazing time, and discussing monensin or other herd strategies with your vet.
What Is Acute Bovine Pulmonary Emphysema and Edema in Ox?
Acute bovine pulmonary emphysema and edema, often called fog fever or atypical interstitial pneumonia, is a sudden lung disease seen most often in adult cattle on pasture. It causes swelling and damage in the lungs, making it hard for affected animals to move air normally. In severe cases, an ox may show dramatic respiratory distress or die suddenly.
This condition is classically linked to a recent move from dry forage onto lush, rapidly growing pasture. Outbreaks often affect a group of cattle, although only some animals become critically ill. Nursing calves are usually not affected, and the disease is most common in mature cattle with higher forage intake.
One frustrating part of fog fever is that mild cases may recover with time, while severe cases can decline very quickly. Because handling and exercise can sharply worsen breathing effort, a calm environment and prompt veterinary guidance matter right away.
Symptoms of Acute Bovine Pulmonary Emphysema and Edema in Ox
- Fast, shallow breathing
- Labored breathing or obvious respiratory distress
- Open-mouth breathing
- Extended head and neck while breathing
- Loud expiratory grunt
- Drooling or frothy saliva at the mouth
- Reluctance to move or worsening distress with exercise
- Sudden death
- Reduced appetite or subdued behavior
- Crackles or harsh lung sounds later in the course
When to worry is early. Any ox with rapid breathing, open-mouth breathing, neck extension, grunting, or distress after a recent pasture change needs urgent veterinary attention. Avoid driving, chasing, or forcing movement, because even mild exercise can sharply increase oxygen demand and may trigger collapse or death in severe cases.
What Causes Acute Bovine Pulmonary Emphysema and Edema in Ox?
Fog fever is most strongly associated with a sudden change to lush pasture. In the rumen, the amino acid L-tryptophan from rapidly growing forage can be converted by microbes into 3-methylindole, a compound that damages the lungs after it is absorbed and metabolized. The result is pulmonary edema, interstitial emphysema, and severe breathing difficulty.
The classic pattern is an outbreak in adult cattle 5 to 10 days after turnout onto better pasture, although signs may develop within about 1 to 14 days in some field reports. It is seen most often in mature beef cattle, but dairy cattle and bulls can also be affected under similar management conditions.
Risk rises when cattle are moved abruptly from dry feed or poorer pasture onto rich regrowth. Lush meadow grasses, alfalfa, ryegrass, small grain forage, turnip tops, kale, rape, and other rapidly growing forages have all been associated with outbreaks. The disease is often most noticeable in late summer or fall, but it can occur whenever forage conditions and management changes line up.
How Is Acute Bovine Pulmonary Emphysema and Edema in Ox Diagnosed?
Your vet usually diagnoses fog fever based on a combination of history, herd pattern, and clinical signs. A recent move onto lush pasture is a major clue, especially when adult cattle develop sudden respiratory distress without the typical fever-and-cough pattern seen with many infectious pneumonias.
On exam, your vet may find fast breathing, increased breathing effort, open-mouth breathing, grunting, and surprisingly quiet lung sounds early on. Later, harsher sounds or crackles may be heard. Because handling can worsen distress, the exam is often kept as low-stress as possible.
Diagnosis also involves ruling out other causes of severe breathing trouble, such as infectious pneumonia, allergic reactions, toxic exposures, or other forms of interstitial lung disease. If an animal dies, necropsy can strongly support the diagnosis. Typical findings include heavy, non-collapsing lungs with edema, emphysema, and sometimes large air-filled bullae.
Treatment Options for Acute Bovine Pulmonary Emphysema and Edema in Ox
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Urgent farm call or herd consultation
- Low-stress visual exam and breathing assessment
- Immediate removal from lush pasture when feasible
- Good-quality hay and quiet confinement with minimal handling
- Basic supportive medications if your vet feels they are appropriate for the individual case
Recommended Standard Treatment
- Farm call, full physical exam, and herd history review
- Low-stress treatment plan for the affected ox plus herd-level recommendations
- Supportive medications commonly used in practice, such as anti-inflammatory therapy, only if your vet judges them appropriate
- Monitoring plan for breathing effort, appetite, and additional herd cases
- Pasture management guidance, including hay before turnout and gradual reintroduction strategies
Advanced / Critical Care
- Emergency assessment with after-hours or referral-level fees
- Trailer transport only if your vet believes the ox can tolerate it
- Intensive monitoring and higher-level supportive care
- Oxygen support where available
- Additional diagnostics or hospitalization attempts in selected high-value cases
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Acute Bovine Pulmonary Emphysema and Edema in Ox
Bring these questions to your vet appointment to get the most out of your visit.
- Does this look most consistent with fog fever, or do we need to rule out infectious pneumonia or another lung problem?
- Is this ox stable enough to stay on the farm, or is referral worth discussing?
- How should we move or confine this animal without making the breathing distress worse?
- Which supportive medications make sense in this case, and what benefits or limits should I expect?
- Should the whole group come off this pasture now, or only the visibly affected animals?
- What pasture management changes would lower the risk for the rest of the herd this week?
- Would monensin or another prevention strategy fit this herd before future pasture changes?
- What warning signs mean I should call you back immediately or prepare for sudden losses?
How to Prevent Acute Bovine Pulmonary Emphysema and Edema in Ox
Prevention is centered on pasture management, because there is no reliably effective treatment once severe fog fever develops. The goal is to reduce sudden intake of lush, high-risk forage. Common strategies include feeding hay before turnout, limiting early grazing time, and increasing pasture exposure gradually over several days.
Other practical options include using suspect pastures before they become very lush, delaying use until after a hard frost when appropriate for your region, and using strip grazing to control intake. Some herd managers also start with less susceptible stock, such as younger cattle, before turning mature animals onto rich regrowth.
For herds with a known history of fog fever, talk with your vet about whether monensin fits your operation. Merck notes that monensin or lasalocid can reduce formation of the lung-damaging metabolite in the rumen when used preventively, but these products are not helpful after signs begin. Your vet can help match the prevention plan to your forage, season, class of cattle, and local regulations.