Treatments vary for summer pneumonia
BRD (bovine respiratory disease) is one of the biggest challenges for the beef industry, especially in feedlot cattle. It can also be a problem in younger calves, in some cow-calf herds. Pneumonia (infection in the lungs) can affect calves of any age. Most of the pathogens that cause pneumonia are already present in the environment or carried by other cattle, and some bacteria live harmlessly in the calf’s upper respiratory tract. They become a problem in the lungs when immune defenses are compromised, such as by viral infections or stress. Stress may be due to bad weather, extreme changes in temperature, a long truck haul, overcrowding in a dirty environment, co-mingling calves from multiple sources, etc. Nutritional stress can be due to deficiencies of an important mineral like copper or selenium.
One of the most frustrating respiratory infections in pre-weaned calves has been called “summer pneumonia” and the cause is not always easy to determine. “Pre-weaning pneumonia in beef calves is a condition we’re still trying to understand better,” says Russ Daly, DVM (Extension Veterinarian/Associate Professor, South Dakota State University. “It can be difficult to identify risk factors. We can understand the stress of transport, weaning, dusty corrals, and factors that affect pneumonia in feedlot calves, but those stresses oftentimes are not factors with summer pneumonia.”
He was part of a multi-state case-control study in 2012-2013, looking at herds that had numerous cases of pre-weaning pneumonia—comparing them with nearby herds that did not have problems. “We were trying to see if there were differences in how they manage and co-mingle cattle, move cattle, or administer vaccination programs,” he says.
“We know that not all pre-weaned calf pneumonias have the same risk factors. Typically there are 2 scenarios. One is in younger calves, one or two months old. They might not have had adequate colostrum to protect them from those early infections.”
The other group is older calves out on pasture with their mothers. “They might be losing their maternal antibodies around the same time. Sometimes what they’ve had (or not had) in terms of vaccines can make a difference, in when they get pneumonia and how severe it is,” says Daly.
There’s generally not a large death loss with pre-weaning pneumonia. They often respond well to treatment, and some may recover without treatment. “They generally recover if treated with appropriate antibiotics but it’s harder to find and treat them in big pastures or summer range,” he says.
The fact that antibiotic treatment is helpful indicates the infection is bacterial or an initial viral infection was complicated by secondary bacterial invaders that respond to treatment. “Most cases of pneumonia (regardless of the age of the animal) are bacterial by the time we see them. The primary viral infections like BRSV or bovine respiratory coronavirus simply set up those calves for a bacterial infection,” Daly explains.
“Just having a good viral vaccine program (vaccinating calves before pasture turnout) is not enough to completely protect those calves; we still see disease in some herds.” Stimulating the calf’s immune system as early as possible makes sense, but this often means we are trying to vaccinate a very young calf, which may not work very well.
“The immune system of calves less than a month old usually isn’t geared up yet to mount a good response. Giving the vaccine isn’t harmful, but you just don’t get the results you’d get with older calves,” says Daly.
It helps to try to minimize young calves’ exposure to other populations of cattle such as stockers or feedlot cattle, or neighbors’ herds across the fence. “If we can limit those kinds of interactions and not bring new animals into a herd without keeping them separate for a while, this may be beneficial.” Herds mingling on rangeland may be a risk. One herd may expose the other to something that doesn’t affect the source cattle at all, but the naïve cattle are susceptible.
Dr. Eugene Janzen (Professor Emeritus, University of Calgary) says the biggest difficulty he sees for many producers and their veterinarians is sorting out the differences between various recommendations for vaccination. “When talking about what we must do to help a calf develop adequate immunity, we have to realize that one size does not fit all,” he says. “The thing we often overlook is risk. There is also controversy about which vaccines are most effective,” says Janzen.
The main thing is to tailor the program to your own situation. If you take your cattle to a community pasture or they are out on summer range with other herds, you might vaccinate them a different way than if they stay home.
“Dr. Amelia Woolums (Mississippi State University) has also described how various factors can possibly lead to ‘summer pneumonia’ in calves,” says Janzen. If producers use AI and gather the cattle in mid-summer, sort the calves away temporarily to AI the cows, and have them stressed and congregated in a dusty pen, those calves may be at risk for respiratory disease.
Daly says there may be some stress on those calves—depending on the length of time they are separated from mom. “Often those calves are in close contact with one another. If some are shedding a lot of pathogens they may expose the other calves,” Daly explains.
A period of multiple very hot days and cold nights, coupled with dusty conditions, etc. might be a factor. “Extreme swings in temperature tend to allow pathogens to thrive in the nasal passages. This can affect the way those pathogens colonize in the respiratory system,” says Daly.
“We can’t make general recommendations about vaccinating calves,” says Janzen. “It’s probably up to the veterinarian who knows that client’s operation, to give specific advice and make a plan for that group of cattle. It all depends on what they are doing,” he says.
There is also the question of maternal antibodies from colostrum interfering with vaccination in a young calf; since the calf already has the antibodies, the immune system sees no need to respond to the vaccine to create antibodies.
“In spite of this situation, however, there is research to show that the body remembers. Even if the calf is not at risk for those diseases in summer, and doesn’t develop a great response, the vaccination still stimulates a little ‘memory’ and the body responds anamnestically (a secondary response to an immunogenic substance after serum antibodies can no longer be detected in the blood). The next vaccination later—such as at weaning time–acts as a booster.
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