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Cow asthma: lush pastures pose risk

by Wyoming Livestock Roundup

    As cows move from dry summer pastures to more lush lower meadows, UW Extension Beef Specialist Steve Paisley says to beware of pulmonary emphysema, or cow asthma.
    Cow asthma is a nutritional disease that occurs when rumen bacteria convert an amino acid, tryptophan, to a toxic compound that causes an allergic reaction in the lungs. Because late-summer moisture in parts of Wyoming has caused some lower meadows to green up, this can increase the risk of cow asthma occurring when cows are moved in for the winter.
    “Generally in Wyoming cow asthma occurs when cattle are moved from dry summer pastures to more lush irrigated pastures in the fall,” says Wyoming State Veterinary Lab Director Don Montgomery. “It can occur as a herd outbreak with several animals affected or with only one affected, but it usually occurs within two weeks of the pasture change.”
    He says the disease usually affects adult animals and that younger animals are less susceptible. “The disease is involved with the process of the rumen’s metabolism of lush grasses, so there may be more poison produced by more mature rumen flora,” he explains.
    Symptoms of cow asthma are labored respiration, with heads commonly held low and stretched out.
    “You really do have to be careful with these animals, because if they’re stressed and forced to move rapidly they can just keel over and die,” says Montgomery. “Their lungs are so severely compromised that any kind of forced movement or excitement can push them over the edge.”
    Wyoming Assistant State Veterinarian Jim Logan says at that point it’s important to work them slowly because they can die from suffocation simply from the exertion.
    Paisley says it’s the sort of situation where you leave the dog in the pickup. “You can trail them off the meadows, but you can’t startle them or run them.”
    Montgomery says there aren’t really treatment options available. “Generally you just need to handle the cattle only if necessary, and if you do, to do so slowly. Medical treatments haven’t been used with a great degree of success. Some may use anti-inflammatory treatments, but when there are large numbers affected it’s not really feasible.”
    Logan cautions that the disease can leave an area for bacteria to multiply, increasing the risk for pneumonia after an occurrence of cow asthma. “Typically it’s a good idea to get them on an antibiotic, after coordinating with a local veterinary practitioner,” he says.
    Paisley says the disease is pretty transient. “If you get them off the pastures the bacteria will stop producing toxin and they’ll come out of it,” he says.
    Montgomery also recommends feeding high quality hay as both a treatment and prevention. “The best way to treat this disease is to prevent it. Introduce the cattle to lush pastures gradually, if you can graze on adjacent pastures and move back and forth between them. A producer can also feed good quality hay prior to and during introduction to the pasture,” he notes.
    He also suggests waiting until after a very heavy freeze in the fall to use the lush pastures, or to pre-graze with sheep or cattle that are less than a year old. Another option is to cut and windrow the pastures. “There are quite a few management things you can do to prevent cow asthma,” he says.
    Paisley recommends treating cattle with ionophores such as Rumensin and Bovatec prior to introduction to new pastures. “If you think cow asthma is a possibility you can get the drugs into them before moving them onto the meadows,” he says.
    “It can be a serious disease once it occurs,” says Montgomery. “If producers have any questions or suspect a case they should talk to their vet.”
    Although the disease can be diagnosed at the State Vet Lab and it can be readily diagnosed in animals after they die, there is no specific test for the disease in a live animal. “There are a lot of other look-alike infectious diseases, like pneumonia, but the association with moving to lush pasture increases the suspicion for this disease,” explains Montgomery.
    Pulmonary emphysema isn’t seen in sheep for the same reasons it is seen in cattle, says Montgomery. “There are a whole lot of things that can trigger damage to the lungs, but cattle are the only true species where we see it associated with the change to lush pasture,” he says. “Sheep are very resistant, and that’s why you can run sheep ahead of cattle on these lush pastures.”
    This fall, with the cold weather Wyoming has already had, Montgomery says most pastures have probably already started to wilt with heavy freezes and therefore pose less of a danger.
    However, Logan says he’s seen occurrences of the respiratory disease as late as the day before Thanksgiving, and that producers should continue to be aware of the condition of their pastures when turning cattle out until they’ve had several hard freezes.
    Christy Hemken is assistant editor of the Wyoming Livestock Roundup and can be reached at

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