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.

In-herd comparisons

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,
he adds.

“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.