This time of year, it is possible to move cattle off mature, dormant warm-season pastures onto cool-season pastures, which are lush, high in protein, wet and rapidly growing. However, in this situation, acute bovine pulmonary edema (ABPE) might be a concern. ABPE is more common in the fall than in the spring. This form of pneumonia typically occurs when cows are fed an all-dry dormant stage of growth forage and then are turned out on high-protein, wet pastures. A typical scenario is a grazing change in the late summer or fall from dry pastures to lush forage regrowth following haying.
ABPE can be avoided by introducing cattle to cool-season pastures over time. For example, limit their access to a few hours for a couple of days, then allow them to graze for a couple of mornings before letting them run full time on the pasture. This is much less of an issue if the pasture is mixed with small grains.
However, grazing management—not the forage—dictates the prevalence of ABPE. Swathing a section of the grass and allowing it to wilt before the animals eat it reduces the incidence. Feeding an ionophore, something with Rumensin or Bovatec, also helps reduce the chances of ABPE and improves the diet’s energy value. Consider feeding a couple pounds of MFA Full Throttle to balance the energy-to-protein ratio and add vitamins, minerals and an ionophore. Preventing ABPE is crucial because there is no effective treatment for affected animals.
Technically speaking, here’s why it happens. The lush, rapidly growing pastures contain an amino acid called tryptophan—a normal component found in protein. Rumen bacteria metabolize the tryptophan, converting it into a compound called 3-methylindole. This compound, in turn, is converted into another toxin that creates edema in the lungs. This fluid interferes with the breathing process and exchange of oxygen and can lead to animal mortality.
Because of the way we feed dairy cows, ABPE usually only occurs in beef cattle. Clinical signs of ABPE usually occur one to 14 days after an abrupt change in pasture, and death may follow in two to four days. Clinical signs are progressive. Animals may exhibit labored, shallow breathing, panting, an open frothy mouth and extended neck and head—all signs that the animal is having trouble breathing.The elasticity of the lung tissue is reduced, so the animals’ inhalation and exhalation are difficult.
Cattle that have been allowed to remain on dry, overgrazed range land are prime candidates for contracting ABPE. These animals will tend to be hungry and will often overeat when presented with lush, green pastures. Research has demonstrated that after two or three weeks of poor-quality forage with protein less than 6.5 percent and acid detergent fiber greater than 50 percent—something like corn stalks—the rumen conditions become conducive for elevated 3-methylindole production.
If an outbreak of ABPE occurs, all animals should be removed from the lush pasture and fed good-quality hay with at least 11-percent crude protein and 58-percent total digestible nutrients. Animals with ABPE have breathing problems and should not be chased nor spooked nor handled in any manner that will increase their oxygen needs.