Calves often victims | Weaning, vaccinating and castrating the same day overwhelms immune system
BANFF, Alta. — Bovine respiratory disease remains a major cause of sickness and death in beef and dairy calves, despite the availability of respiratory vaccines and treatments.
“How much bovine respiratory disease you get varies from year to year,” said veterinarian Anthony Confer of Oklahoma State University.
Most severe and fatal forms of BRD resulting from stress are traced back to bacteria, including mannheimia haemolytica and mycoplasmal pneumonia, he told a beef conference held in Banff last month.
The disease can be unpredictable. Beef cattle bacterial pneumonia occurs within the first six to eight days after a stress such as shipping or commingling. The animals may receive treatment but never do as well as they should.
A study from the United States estimates BRD costs the industry $500 million a year.
A western Canadian feedlot study found that 10 to 30 percent of calves bought from auction markets were treated for BRD with a fatality rate of five to 10 percent.
Agriculture Canada researcher Karen Schwartzkopf-Genswein said compromised animal welfare results in stress, which suppresses the immune system and puts animals at risk.
Calves may be weaned, castrated and vaccinated all in one day, which is highly stressful.
“We know the combination of all these management procedures done at one time really overwhelm the ability of that animal to cope in its environment. What we get is a bunch of sickness or a bunch of mortality,” she said.
Preconditioning has been around a long time and helps animals adjust when they leave the home farm. Softer weaning practices can also reduce stress.
For example, calves that are abruptly weaned and transported the same day show a higher level of sickness than those that were fence line weaned.
Slowly weaned calves demonstrate greater weight gain than abruptly weaned calves two weeks after weaning. There is also a lower incidence of pneumonia among the fence line weaned calves.
Confer said transportation is another major factor.
Long distances and possible exposure to air pollutants such as diesel exhaust may also have an effect. He said it has not been proven that diesel fumes are a problem, but there are pollutants that could effect tracheal cells.
Weather effects have not been proven, but maximum wind speed, wind chill and temperature change do correlate with increased incidence of disease.
Management effects such as commingling cattle from various sources have been shown to increase disease.
Feed and micronutrients are sometimes thought to help, but Confer was skeptical.
“You can’t feed your way out of a respiratory disease.”
He is also dubious about the benefits of chromium, copper and zinc supplements.
“Overall with many of these, no overall effect has been shown with these micronutrients and BRD,” he said.
It has been suggested that genetics may have a role, with quieter cattle seeming to have less BRD and better weight gains.
However, Confer said breeding for disease resistance may not work. Researchers have shown that heritability for BRD resistance is low, and a study on crossbreds did not show any particular disease resistance.
As well, pathogens are always changing, which means genetic selection may not work because viruses and bacteria are constantly evolving.
“If we breed for resistance to BRD today, will that resistance hold up five years down the road?”
With pneumonia, bacteria overwhelms the animal’s defence systems and the infection spreads within the lung, causing considerable damage.
It is not contagious in the same way as a virus.
“It is not like a viral infection where one calf comes in and infects all the others,” Confer said.
It appears during stress, with the normal flora of the respiratory system changing and causing diseases. Mixed infections are also common: 40 to 77 percent in bovine pneumonia.
“You have to start thinking that bacterial pneumonia is a very dynamic process,” he said.
Viruses may also enter the system and do further damage. The viruses modify the respiratory tract and diminish the host’s immune response to bacteria so that they can replicate easily.
Some viruses cause serious disease by themselves, such as infectious bovine rhinotracheitis.
Bovine viral disease may also be present and cause extensive damage to the immune response.