By Obioha Durunna, Ph.D.,P.Ag. Regional Livestock Specialist, Prince Albert
Many producers move their cattle to new lush pastures this time of the year. If the pasture you are moving from was dry or overgrazed, your cows may be exposed to the risk of developing Atypical Interstatial Pneumonia (AIP). This respiratory disease also goes by other names such as fog fever or acute bovine pulmonary edema and emphysema (ABPEE). Further, if you had some mortality or observed some of your cows are struggling to breathe after you had recently moved them into greener pasture, your cows may have developed the disease.
What is AIP?
AIP is an irreversible lung condition that occurs in both sexes of beef and dairy adult animals, but adult beef cows are mostly affected. Nursing calves are not affected.
As summer advances into fall, producers may move cattle into new fields that haven’t been grazed. These fields may be lush from late precipitation and will most likely have better feed quality compared to the previous dry pasture that the cows have been grazing. Consequently, such rapidly growing or lush pastures will have higher protein content than the old fields, causing the move to have undesirable consequences.
Lung damage occurs when adult cattle that were previously on dry or overgrazed pasture for an extended period of time are moved into lush pastures (such as alfalfa, small cereal grains, ryegrass or kale). Such prior feeds or pastures are characterized by low dietary protein (below 6.5 per cent crude protein) and very high fibre (less than 50 per cent Acid Detergent Fibre). If the cattle spend a prolonged period of time on the low protein feed, it conditions the rumen microbes to such poor quality feed.
An amino acid triggers lung damage
L-Tryptophan is an amino acid that has been identified as the issue because the rumen microbes convert it into a toxic metabolite called 3-methylindole (3-MI) which causes damage in lung tissues. As more tryptophan compounds are converted to 3-MI by rumen bacteria, they enter the blood stream and do more damage to the lungs causing edema and emphysema. This damage reduces the oxygen exchange capacity of the lungs.
Signs and Symptoms
AIP can also be described as a nutritional or management issue and therefore is not infectious or contagious. As cattle are moved abruptly from a dry poor quality feed to a lush pasture, symptoms can develop within seven days of the move. Affected animals may show signs of difficulty breathing with loud grunts without coughing, or mild cases may go unnoticed. The lungs of affected animals are filled with frothy fluid. Shortage of oxygen causes faster heart rate (up to 150 beats per minute) and may lead to a heart attack.
Prevention and treatment of affected animals
Producers can adopt some strategies to prevent or manage the issue. If you recall that a previous move to a pasture had induced AIP, it may be a good idea to exercise caution when moving animals into that same pasture. You can gradually introduce forage from the new pasture to the animals while they are still on the dry feed. This could be achieved by harvesting and baling the lush forage. This strategy will enable the rumen microbes to gradually adapt to the new feed.
You may also limit the grazing area that such cows can access thereby reducing the amount of lush forage consumed. This strategy can be combined with feeding hay to the cattle before they are turned out to the lush pasture.
Producers can also graze risky pastures with cattle that are less than 15 months old, because they are less susceptible. Feeding monensin to cattle one day before turnout to the lush pasture may inhibit the bacteria that generate the 3-MI thereby reducing the risk of AIP. You can also allow the pasture to be more mature before grazing.
There is no known effective treatment because the damage to the lungs cannot be reversed. Your best option might be emergency slaughter of affected animals. Antihistamines or anti-inflammatories may help to provide some relief and minimize the conversion of the 3-MI into the toxic metabolite. Feeding monensin after the cows have developed the disease may not be useful. Avoid introducing any form of stress (such as moving the affected animals) as this may exacerbate the issue leading to exhaustion and death.