Pneumonia seems to be a constant stalker of calves, and for good reason. Most of the bacterial pathogens that cause it are present in the calf’s upper respiratory tract; they just need the opportunity of an immune system compromised by viral infections
Summer pneumonia is among the most frustrating respiratory infections in nursing calves. The cause is elusive, and many cases occur during seemingly non-stressful conditions for the calves.
A multistate team of researchers is studying ranches in Nebraska and the Dakotas affected by the problem, and comparing them with ranches in the same veterinary practices that haven’t experienced the disease. The team includes Russ Daly, South Dakota State University; Jerry Stokka, North Dakota State University; David Smith, currently at Mississippi State University but formerly at the University of Nebraska; and Amelia Woolums, University of Georgia (UGA).
Smith, an epidemiologist, investigated outbreaks in Nebraska herds for several years. He consulted with Woolums to design the study because of her expertise in immunology and vaccination to control respiratory disease in cattle.
“We know a lot more about weaning and post-weaning respiratory cattle disease in calves, and how to prevent and treat it,” Daly says. “Basically, the lesson is that if we minimize calves’ stress levels and do a good job of early vaccination, we tend to see fewer problems,” he says.
However, there’s little data regarding the risk factors for summer pneumonia. “We want to understand why some ranches perennially have a problem, and others never do,” Woolums says.
Daly says what’s frustrating about pneumonia in nursing calves is that reduced stress and good vaccination programs don’t seem to prevent the disease as uniformly as they do for post-weaning respiratory problems.
“There may be management practices in some herds that put cattle more at risk. For instance, gathering cattle for artificial insemination (AI), sorting, exposure to dust, etc., may favor virus transmission or compromise the immune system. We don’t always know which factors might be important,” Smith says. In some herds, the pneumonia occurs in calves out on the range, absent of those activities.
“We’re looking at farms with summer pneumonia cases and comparing them with farms in a similar location and time that haven’t had issues,” Daly says. “We want to discover the factors that favor calf health on some farms, or that could help producers prevent this disease. Of course, environmental factors are hard to control, but at this point, we don’t even know if these are involved.”
He says some operations have problems in June and July. Others have sickness in very young calves, while some have pneumonia in calves a month before weaning. While these latter calves will respond to treatment, their weight gain takes a hit.
“If pneumonia happens close to weaning, that calf might not be able to be sold with the rest of the group. There’s also the issue of long-term damage and scarring in the lungs; those calves just don’t do as well later,” Daly says.
Looking at multiple factors
The study is looking at various factors, such as gathering cows and calves for AI or branding. “The calves are only apart from their mothers for a short time. We wouldn’t think it could be enough stress to affect them, but perhaps this handling facilitates transmission of bacteria or viruses,” Daly says.
Or perhaps multiple factors are at work. On some operations, for instance, ranchers move cattle for intensive grazing, or subpopulations are commingled at different times.
“Commingling cattle from different sources is a well-known risk factor for feedlot bovine respiratory disease. We don’t know if commingling young calves from different subpopulations on the same ranch increases the risk,” Woolums says.
When cattle on the range are moved to new pastures, stress could be a factor if it’s hot, dusty or a long drive. But what about cattle that aren’t being moved or handled?
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“Cattle diseases like calf scours are often multi-factorial; summer pneumonia may be, too,” Daly says. Colostrum intake has been looked at, along with calves’ ability to respond to vaccine at different ages. Weather, like a late-spring storm or a cold, rainy spell in early summer, might be a contributing factor in some situations.
“A respiratory pathogen may be circulating, with some unapparent mild infections, and a little extra stress might put them over the edge,” Smith says.
There may be genetic differences in calves’ ability to mount a good immune response as well. “We’re just scratching the surface of that possibility,” Daly says. “We know crossbred cattle have hybrid vigor, and part of that characteristic includes hardiness and
The study revolves around case herds that treated at least 5% of their preweaned calves. These are compared with nearby herds (the control animals) that treated less than 0.5%.
“We’re looking at about 30 cow-calf operations that had respiratory cattle disease this past summer. For each of those, we’re looking at two control herds, randomly selected, from the same veterinary practice,” Daly explains.
Woolums has three UGA veterinary students conducting blind interviews. “They don’t know if it’s a ranch with or without summer pneumonia. They just ask questions about management — how many acres the cattle run on, are they in one group or multiple groups, are they segregated by age, are calves creep-fed, and so on,” she explains.
Thus far, 50 operations have been interviewed — both case and control herds. The aim is to enroll between 75 and 90 farms and include information about the spring 2012 and 2013 calving seasons, she says.
Analysis of herd-level risk factors is another aspect of the research, and management practices of the herds will be compared. “We hope to find differences that may provide clues to the cause of summer pneumonia. However, at this point, we’re simply identifying management practices associated with summer pneumonia. But just because two things are associated, doesn’t necessarily mean that one causes the other,” Woolums explains.
“In future research, we might modify one or two things in some herds, and not modify those things in other herds with summer pneumonia; then we’ll see if there’s a difference in outcomes. This would provide stronger evidence regarding practices that truly cause summer pneumonia,” she adds.
The researchers also are gathering additional data from problematic herds. “If they have individual calf treatment records, we ask them to share those with us,” Woolums says. “Then we’ll compare characteristics of calves contracting summer pneumonia with calves that don’t. That’s the calf-level, risk-factor analysis.”
Age of calves also can be a factor. For instance, are they still protected by colostrum antibodies, or did a calf receive adequate colostrum to begin with? One of the differences they’ve observed is that the age of the dam plays a role.
“We also see this with calf scours, in that first-calf heifers may not give their calves as much immunity through colostrum,” Woolums says.
Such calves are more prone to respiratory disease and/or scours due to inadequate protection, simply because of fewer antibodies in heifer colostrum compared to that of an older cow. Older cows may also have a larger quantity of colostrum, as well as better maternal bonding skills that favor the calf nursing sooner.
“We’re looking at which animals get sick, and when,” Smith says. “Two patterns are emerging. Some herds have sickness in young calves [less than 60 days], but these cases tend to be sporadic.” Perhaps these are due to less resistance in individual calves, or the calf didn’t get enough colostrum and is at risk at an early age,
“The other pattern is outbreaks where many calves get sick. These tend to be older calves, 120 to 150 days of age. This could be because the majority of those calves have passed beyond the coverage of the maternal antibodies, but haven’t yet mounted enough of their own immunity,” Smith says.
There may be other explanations as well. For instance, the pneumonia may be occurring during a season when the environment favors virus pathogens, or certain management factors make pathogen transmission easier.
“The problem in sorting this out is that calves in well-managed herds are about the same age. They move into that window of susceptibility at about the same time. Is it something related to the calendar or season, or to the age of the calf?” Smith asks.
Questions on vaccination
Some producers have begun vaccinating calves at turnout, or are adding respiratory vaccines to branding-time protocols. This may help, depending on the age of the calves and the products used, the researchers say. Success may depend on whether the calves are old enough that their immune systems can respond to vaccination, since maternal antibodies from colostrum may interfere.
“Some research suggests that calves 60 to 90 days of age can respond to vaccination. In some instances, they do; sometimes, they don’t,” Woolums says.
Calf age at branding can vary greatly. The oldest might be 2 to 3 months old, while the youngest might be only a week old.
“A week-old calf isn’t likely to respond adequately to vaccination. A dairy calf that received no colostrum can respond to vaccine at a week of age, but a beef calf that received good colostrum won’t reliably respond. So it depends on the proportion of the herd that is 1 to 2 weeks old, vs. the proportion that might be 2 to 3 months old. If the proportion of really young calves is small, it may not be a problem,” Woolums explains.
Age at vaccination is an important aspect. “The other piece of that challenge is that even if you know when to vaccinate, you need effective vaccines against the pathogen that’s involved, or you’re just shooting in the dark,” Smith says.
Ranchers should work with their herd-health veterinarian to design a specific strategy for their operation. No one formula or schedule fits all herds, Woolums says.
Regardless of when you vaccinate, and with what, some calves won’t mount adequate immunity for one reason or another. “There is also a genetic component — not just in resistance to bovine respiratory disease, but also in response to vaccination,” Woolums says.
The challenge of sampling
Woolums would like to have a student sample calves when ranchers gather a herd for artificial insemination.
“Then later, if some calves get sick, we could sample them again and see if there’s a difference. One reason there isn’t more research on summer pneumonia is because it’s hard to sample the calves,” she says.
Beef calves aren’t conducive to sampling, except at branding. Calves could be captured during an artificial insemination (AI) program, but not all producers use AI.
“It’s also hard to sample them without changing the risk factors. If we bring them all in to sample them, we’ve grouped them in a situation where they wouldn’t ordinarily have been grouped,” she says. This creates even more risk factors — stress of handling and commingling in close quarters.
Is a virus involved?
Researchers want to find out more about the pathogens involved in summer pneumonia. Woolums says coronavirus is one bug of interest because the virus has been found on nasal swabs of some sick calves.
“But we can also find coronavirus in normal calves. We don’t know if a virus is the actual cause. Just because you find it on the nasal swab doesn’t necessarily mean it’s involved with illness,” she says.
“The fact some herds have more trouble with pneumonia than others might mean they have some pathogens present that are not present in other herds, but we don’t know,” says Smith. “It may be something like bovine respiratory syncytial virus or bovine virus diarrhea that is making them more vulnerable to other respiratory pathogens.”
Survey seeks disease associations
Woolums says earlier work on summer pneumonia seemed to indicate that certain management practices are associated with summer pneumonia.
“We mailed a list of questions to producers in Georgia, Florida, West Virginia, Kansas, Iowa and Nebraska, asking about their management and whether they had calf pneumonia. We did find some significant associations,” she says.
“We asked whether the producers saw any calves with respiratory disease, and also the proportion of calves they treated for pneumonia. Some things were associated with whether they saw respiratory disease, and different things were associated with the proportion of calves they treated. For example, if a farm had calf diarrhea, they were more likely to also see calves with respiratory disease. And farms that used artificial insemination were more likely to treat a larger proportion of their calves,” she says.
Depending on the conditions — whether it was low-stress handling, if the weather was hot or inclement, or corrals were dusty — there might have been factors making them more vulnerable. “It’s also possible that when calves are sorted away from their mothers and grouped together, they have more opportunity to spread respiratory viruses or bacteria among themselves,” she says.
Heather Smith Thomas is a rancher and freelance writer based in Salmon, ID.
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