Small lungs make cattle prone to respiratory diseases

Bovine respiratory disease costs the North American beef industry about $1 billion every year, said researchers from the University of Calgary veterinary school.

And it’s always likely going to be a difficult problem to control be-cause cattle are susceptible, said Edouard Timsit at the veterinary school’s annual beef cattle conference held in Calgary last month.

“Cattle are and will be more susceptible to pneumonia than other species because of their anatomy.”

When young animals leave the farm, they go through a series of stress factors that challenge their immune systems. Even if they were vaccinated, sickness can occur following weaning, commingling with unknown cattle, transport and inclement weather.

“They go through the same kind of viral exposure as children in a day care,” said Timsit.

Cattle have a high oxygen requirement, but proportionately small lungs compared to horses, people or dogs.

Cattle respiration is 30 breaths per minute, compared to a horse at 11 breaths.

Bacteria and contamination can more easily enter cattle lungs and that can cause a range of different strains of pneumonia.

Broncho pneumonia is the most common where bacteria such as mannheimia haemolytica, pasteurella multocida, histophilus somni and mycoplasma bovis can enter the respiratory system.

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Pneumonia often occurs after weaning and transportation, and within 50 days at the feedlot, calves become sick. Many respond well if they receive antibiotics early.

Interstitial pneumonia can enter the cattle’s blood system and cause lesions between the cells. This form affects two to three percent of the feedlot population.

It is sporadic and heifers seem to be more at risk. The animals may display an open and frothy mouth and may not have a fever.

Necropsy shows overinflated lungs, interlobular edema and emphysema with a checkerboard pattern — rubbery or dark lobules interposed with normal to pale, overinflated lobules.

Steroidal anti inflammatory drugs and antimicrobials can help but the prognosis is guarded, said Timsit.

Embolic pneumonia shows multiple abscesses of the lungs. Cattle with embolic pneumonia can hemorrhage and may have a bloody nose, anorexia and fever.

“Most of them die within two days,” Timsit said.

Research into identifying the four main bacteria contributing to pneumonia, as well as potential antimicrobial resistance, is underway.

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Considerable information has been gathered on mannheimia haemolytica, but less is known about the other bacteria, said Samat Amat, a PhD candidate at the University of Calgary.

“The clinical impact of BRD continues to be increasing with in-creased metaphylactic use,” he said.

Many feedlots give all cattle antibiotics upon arrival to try and stave off later infections.

Working with four commercial feedlots, the research found the most common bacteria was pasteurella multocida, while histophilus somni was the least prevalent.

However, samples collected from healthy cattle also found these bacteria in nasal cavities and other parts of the respiratory tract.

Researchers also found multi drug resistance to four commonly used antimicrobials among sick and healthy cattle, including tetracycline, neomycin and macrolides, as well as tulathromycin, the main ingredient in Draxxin.

“There is a need to find an alternative,” Amat said.

He is also working on a probiotic and essential oils that could be used as an additional treatment.

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