The Agriculture Canada Lethbridge Research Centre has identified a possible cause of Acute Interstitial Pneumonia, a cattle disease with a fatality rate of 30-50 percent.
In a two-year field study of southern Alberta feedlots, researchers found high levels of toxic metabolites in the blood plasma of cattle killed by AIP.
Those metabolites, which damage lung tissue, are derived from a compound called 3-methylindole.
“The results are the first that point to 3MI as a possible cause of AIP in feedlot cattle,” said researcher Tim McAllister. “By establishing that link, we have a much clearer target for finding ways of preventing the disease.”
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Though AIP causes less than five percent of feedlot deaths, the disease is costly because it almost exclusively infects heavyweight cattle that are close to slaughter.
The disease is not contagious, but appears sporadically from year to year, and over 90 percent of cases are in heifers. It seems largely confined to southern Alberta, where Canada’s cattle feeding industry is concentrated.
AIP makes it difficult for cattle to breathe and often causes other complications related to stress. Symptoms include panting, frothing at the mouth, lowering of the head, increased respiration rate and grunting. Many diseases have similar symptoms, so scientists have to diagnose AIP under the microscope.
To conduct the study, researchers worked with several commercial feedlots with more than 5,000 head in southern Alberta’s feedlot alley, which includes the 50 kilometre radius around Lethbridge. They collected eight AIP cases for study in 1995 and 42 cases in 1996.
Of the animals studied, the plasma of those killed by AIP contained almost double the level of 3MI metabolites in comparison to that of cattle killed by other respiratory diseases.
Before this research, others had proposed that Bovine Respiratory Syncytial Virus plays a role in the development of AIP, but the study found no evidence of this virus in AIP-infected cattle.
Since indications are the disease is not viral, a range of factors may come into play, said McAllister. Though the results suggest 3MI metabolites cause AIP, researchers don’t know what contributes to the level of 3MI metabolite production and susceptibility.
“It is becoming more apparent that AIP may arise from a complex interaction of feed intake, feed composition, individual animal physiology and possible environmental triggers,” McAllister said.
Since AIP is mainly a problem in heifers, fluctuations in sex hormones may play a role.
Researchers will explore potential contributing factors and examine the disease further in a new three-year study, supported by the Canada Alberta Beef Industry Development Fund. Initially, they will use samples collected from 125 cattle that developed AIP last year.
One aspect of the new study will explore the potential of control through management practice, said McAllister. Increasing the level of cysteine in the diet has been shown to reduce the severity of lung lesions in goats infused with 3MI.
If AIP results from a greater sensitivity of lung tissue to 3MI metabolites due to dust-borne allergens, dust control measures, such as sprinkling of feedlots, may reduce incidence of the disease.
Additionally, there are additives that have been identified that are capable of inhibiting the biochemical pathway.
