A confounding pneumonia striking feedlot cattle without warning may be triggered by a series of events.
Feedlot checkers may not realize an animal has acute interstitial pneumonia until they find a dead one in the pen.
A study based at Agriculture Canada’s Lethbridge Research Centre found this pneumonia, also called AIP, may arise from a complex interaction of feed intake, feed composition, individual animal physiology and environmental triggers like dust.
Since AIP is mainly a problem in heifers, fluctuations in sex hormones may play a significant role.
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Working with a North American research team, beef scientist Tim McAllister reported that a two-year study of southern Alberta feedlots showed high levels of toxic metabolites in the blood plasma of cattle killed by AIP. Those metabolites, which damage lung tissue, are derived from a naturally occurring compound in the body called 3-methylindole.
The disease AIP is responsible for less than five percent of deaths in feedlots but typically occurs in cattle 20-40 days before slaughter.
“In certain months of the year it can suddenly be a very significant cost for the producer because it appears over a limited period in the summer,” McAllister said at the national beef seminar held in Calgary Nov. 16-17. His project was funded in part by the Canada Alberta Beef Industry Development Fund.
The onset of the disease is quick and animals seldom recover. Emergency slaughter is often the only option because they may not survive the stress of transport.
AIP symptoms may resemble other forms of respiratory problems and it can be accurately diagnosed at post-mortem only when lungs are checked for lesions. Symptoms include difficulty breathing, increased respiration, fever, a lowered head, grunting and frothing at the mouth.
The search for common denominators of the disease proved elusive.
Since AIP is mainly a problem in feedlot heifers, the researchers checked those receiving the hormone MGA to suppress heat and improve growth. There was no indication that MGA increased levels of 3-methylindole.
Climate may play a role in that more cases seemed to appear during dry and dusty conditions. Sprinkling pens to reduce dust may help because 66 percent of cases occur during dry periods.
Researchers found Aspirin for therapy was useful if the disease was caught in the early stages. Their test group showed 63 percent survived and could be slaughtered through normal channels while 33 required emergency slaughter and three died before slaughter.
Bovine respiratory syncytial virus was implicated but researchers found no connection when AIP-infected lungs were examined.
