With summer pastures dry in many places, this could be a bad year for acute bovine pulmonary edema (also called emphysema, lung fever, fog fever, bovine asthma and atypical interstitial pneumonia).

Cattlemen should be aware of this possibility when moving cattle from dry pastures to greener ones. The sudden change in feed quality can be disastrous, says Robert Cope, a Salmon, ID, veterinarian.

Affected cattle are often called lungers or panters. The problem hits cattle suddenly when they come off dry grass onto green pasture or irrigated fields. There is a sudden filling of the lungs with fluid, occurring a few days after the change in feed. It's not infectious or contagious. It's like an allergic reaction (similar to human asthma) and can sometimes be successfully treated with antihistamine, cortisone and adrenalin.

The problem seems to be caused by an animo acid called tryptophan, found in lush green forages. After being ingested in the feed, tryptophan may be transformed by gut bacteria into a poison under certain conditions, says James Carlson, animal scientist at Washington State University.

The change from dry, sparse, poor-quality pasture to lush, rapidly growing forage results in an undesirable fermentation in the rumen and production of 3-methylindole (3MI), which is rapidly absorbed from the rumen into the blood, he says. As blood carrying 3MI circulates through the lungs, a toxic intermediate compound is produced that causes lung damage and results in emphysema. Cattle develop difficult breathing one to 14 days after appearance of symptoms.

Cope says this problem "occurs primarily in adult cattle, usually within four to seven days following the pasture change." Affected cattle show severe respiratory distress, and even slight exertion may kill them.

The exertion of being moved from pasture to a corral for treatment may cause the animals to become so short on oxygen that they collapse and suffocate. Sometimes, the best thing to do with a serious case is to leave the animal alone or try to get antihistamine or cortisone into her without distressing her, then leave her alone.

The toxic reaction in the lungs results in extreme constriction of the bronchial passages, says Cope. "This traps tiny bubbles of air in the lungs. This trapped air soon expands to form larger bubbles, allowing less of the lungs to be utilized for gathering oxygen. The demand for oxygen soon outgrows the supply," he says.

Symptoms Appear Suddenly Symptoms come on fast. The most obvious sign, says Cope, is labored breathing, often with grunting or wheezing sounds. The animal may try to breathe through its mouth and may froth at the mouth.

"The tongue is often extended from the mouth, and the mouth is frequently kept open. The nose may seem bluer than usual," he says.

Heidi Smith, veterinarian in Terrebonne, OR, says affected cattle may seem bright and perky (compared to animals with pneumonia); there's no apparent toxemia or high fever. They may still try to eat and drink.

"A cow may stand with head and neck outstretched, mouth open, breathing very rapidly and shallowly. Heart rate rises because of the shortage of oxygen and may get as high as 150 beats per minute," Smith says.

If the heart rate is over 120, the animal is probably in the final stages of the disease and won't last much longer, she adds. Death can occur within 12 hours of the onset of symptoms. Mild cases will recover. Some chronic cases linger for weeks, even months, with periods of partial recovery and then relapse.

Ranchers can usually avoid the problem by not putting cattle into lush, green pasture directly from dry range or dry pastures. A transitional period in a not-so-green pasture, or feeding hay, will usually prevent occurrences.

Take Immediate Action If cattle begin to show signs of emphysema after being moved into a greener pasture, the herd should probably be moved out of the offending pasture into a drier one, taking care not to excite or exert them, Cope says. Severe cases should not be moved but treated, if possible, by a veterinarian.

The problem comes on swiftly. Unless the herd is being checked often, the first indication of trouble may be the discovery of a dead cow.

Cope says he's had "fair success" treating affected cattle with antihistamine. This treatment alone is not enough to save the cow if she's left in the pasture, however. She still must be moved either back where she came from or to a dry lot.

In some areas of the country, entire herds can be affected, Cope says. Washington State's Carlson adds that the problem occurs most commonly in beef cows.

"It's the largest animals with the highest feed intake capacity that most often succumb to the disease," he says.

Carlson adds that the condition occurs worldwide. It has been reported in parts of Europe, Canada and throughout the U.S. In the West, it's often associated with pasture change in late summer or fall from dry mountain range to lush meadows with regrowth following the removal of hay. It can be found anywhere cattle are intensely managed and abrupt feed change occurs.

Most Prevalent In The Fall Outbreaks of emphysema are possible during periods of active plant regrowth in spring and summer, Carlson says, but the problem is most prevalent in the fall.

Occurrence usually coincides with cattle being moved from one pasture to another. The disease occurs on many types of forage including rape, kale, alfalfa, turnip tops, small cereal grain forage, ryegrass, Bermudagrass and mixed meadow grasses. Any lush forage apparently can result in the formation of 3MI when the rumen is not adapted to the new forage. Grazing management, rather than type of forage, is the determining factor in the onset of emphysema, he says.

Proper management of feed and pastures is the best way to prevent cases of emphysema. Dry range years can take a heavy toll, and ranchers should keep this in mind when preparing to bring cattle off range and into the home meadows or fields.

On any pasture, cattle should be moved before they exhaust their current feed supply, Carlson advises. Cattle allowed to remain on dry, overgrazed pasture are prime candidates for trouble.

"These animals will be hungry. When given access to lush forage, they will tend to overeat. Research has demonstrated that after two or three weeks of poor-quality forage - crude protein less than 6.5% and acid detergent fiber greater than 50% - ruminal conditions become optimal for elevated 3MI production," he says. "Whether or not cows have been on overgrazed pasture, provide them with hay or other feed before a grazing transition."

Preventive management includes providing a gradual adaptation to the lush forage of the new pasture. Besides feeding hay, limiting cow access to the new pasture for the first few days will aid the adaptation process, Carlson says. This may mean allowing them only an hour or two of grazing the first day, gradually increasing their grazing time on the new pasture for the first several days before allowing them to remain in it full time.

"For example, allow cows that are full of hay one hour to graze lush pasture. On the second and subsequent days, increase grazing time by one hour over the previous day for the first seven days. The adaptation period gives the rumen microorganisms time to adapt to the new forage and reduces 3MI formation, Carlson says.

Other Management Tips Feeding restricted quantities of mechanically harvested green forage (green chop) in addition to hay will also adapt the rumen to lush forage, he adds.

Other practices that can reduce losses from emphysema include the use of antibiotics (monensin) and/or cutting the pasture before turning in the cows, says Carlson.

"Experimentally, 200 mg of monensin/head/day in at least 1 lb. of grain for one or two days before the pasture change, and for seven to 10 days after the change, has proven to reduce 3MI formation," he says. "Cows fed monensin and given access to pasture containing mowed, partially dried forage had lower ruminal 3MI concentrations than cows fed supplemental monensin alone."

One problem with use of monensin is that some cows may refuse to eat the supplements or won't eat enough of it.

The most important factor in treating this problem is early detection, Cope says. He recommends that all herds be checked closely at least twice a day for the first 10 days after they are brought off the range or moved from dry pasture to green fields.

"Treatment of this condition is not always successful, but we have a chance if the cattle are not too bad off when treatment is begun," he says.

Adult cattle are generally affected most by the change in feed. Calves usually aren't at risk. Thus, one way to avoid losses in range country is to bring cattle home directly to the corrals, instead of putting them into green fields, and weaning the calves. The calves can then be put on the green feed, and the cows taken back to dry pastures.