Acute bovine pulmonary edema and emphysema are two lung conditions that can occur with sudden pasture changes
Acute bovine pulmonary edema and emphysema can occur when animals are suddenly changed from dry pastures to lush green ones or from dry hay to healthy pasture.
Dr. Nathan Erickson of the Western College of Veterinary Medicine at the University of Saskatchewan said problems arise from metabolism of certain proteins, when toxic products end up in the lungs and build to damaging levels that can permanently reduce lung capacity.
“In an acute case there is a profound change in breathing,” said Erickson. “The animal struggles for air, with head extended, panting open-mouthed.”
Affected cattle are often called lungers or panters. They breathe with effort and will grunt and wheeze. Affected cattle have no fever and may seem perky and may still try to eat or drink, which are ways to distinguish it from infectious pneumonia. Respiratory distress is the main symptom, even with slight exertion.
The disease in pastured animals is connected to tryptophan metabolism and formation of 3-methylindole in the rumen. Lush, rapidly growing forage contains an amino acid called tryptophan, a component in protein and most green forages.
This compound is absorbed into the bloodstream and can be further metabolized in the lungs into other toxins that cause lung damage. The toxins in the lungs then produce edema and emphysema, said Erickson.
This fluid interferes with breathing and exchange of oxygen, resulting in severe respiratory distress.
“In Western Canada, the times I’ve had to deal with outbreaks were in the fall when cattle were moved from dry grass pastures into a green annual pasture like ryegrass or something that’s higher in protein than they came off of,” Erickson said.
Animals suffering from the ailment can die if overly exerted.
“People try to treat these animals with antihistamines and steroids, but usually this is not successful. To remove the herd from the pasture, you need to move them very slowly, especially if you try to take some to a facility for treatment. Roping them out in the pasture will probably stress them too much, as well.
“Even if you move the unaffected cattle off that pasture and onto dry feed, a few may still develop problems because it takes a few days for all cases to become clinical. After you get them on dry feed, you’d want to slowly transition them back on green feed at a later date.”
The best prevention is gradual adjustment from dry forage to green forage.
“With electric fence you could temporarily fence off a small portion of the new green pasture and limit the cattle to that for the first day, like about an hour’s worth of grazing time,” Erickson said. “Limiting their first few days allows them to gradually adjust.”
A seven-day transitional period gives rumen microbes time to adapt to the new forage and reduces 3-methylindole production.
“There is some evidence that using an ionophore like Rumensin prior to moving cattle into the green pasture may help reduce incidence of this disease. This alters the bacterial population a bit and reduces the ones responsible for converting that protein.
“This could potentially help, but cattle must be consuming the ionophore for several days before the change in feed, and some may not be eating enough of it.”
Introducing animals into cereal pasture after a hard frost is not entirely effective either, Erickson added. It might take several hard frosts to alter plant protein levels.
A similar illness is sometimes seen in feedlot cattle, but the problem is not necessarily related to protein in feed.
“It is different and we don’t have a good understanding of why it happens in the feedlot,” said Erickson. “In these cases we call it atypical interstitial pneumonia (AIP), though it has similar signs and the same result in the lungs.”