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Management practices can impact frequency of summer pneumonia in calves

by Wyoming Livestock Roundup

David Smith, an epidemiologist at Mississippi State University, says he largely studies infection diseases of cattle with the idea of trying to understand how to manage cattle to prevent problems. 

“Recently, we’ve been studying pneumonia in calves prior to weaning,” Smith explains, noting several management practices can impact pneumonia in calves. “I’m talking about work that’s been done by a large number of people.”

“The tradition in veterinary medicine is to think about a host-agent interaction,” Smith says. “Sometimes we think about what’s going on in the environment, but we often think about the bug and then ask if there is an antibiotic to kill it or vaccine to prevent the infection.”

He continues, “For pneumonia, we have to think broadly, because there are much broader issues that sometimes affect disease ecology.”

Disease challenges

When a calf is born, Smith says there are many hazards the calf faces between the moment it hits the ground and weaning.

“In the first few weeks of life, the calf’s big risks are the weather, injury, predators and disease,” he says. “From three weeks of age until weaning, the leading cause of death in calves is pneumonia.” 

Smith focused on pneumonia, opting to look at what goes on outside the animal that influences the risk in the herd to have the disease.

Disease agents

Further, when looking at the cause of pneumonia, Smith says all bacterial pathogens that may be connected to pneumonia are found in calves, including Mannheimias, Pasturellas, Histophilus, et cetera can be found. 

“We’re confident this is not necessary just a bovine respiratory disease (BRD) problem,” he says. “It may be present in some cases, but it’s not in all cases.” 

Further, Smith says they are suspicious about the role of bovine corona virus.

As antibodies are lost when the calf ages, Smith comments, “It doesn’t matter how high the antibody counts were, they’re gone by 90 days of age.”

While calves can also respond to disease after that point in time, prior to five to eight months of age, the immune response is slower, weaker and easy to overcome.

“There is a point in time when antibodies from colostrum are disappearing and the immune system hasn’t ramped up to full power,” Smith says. “That’s the time calves get sick.”

Risk factors

Smith explains his team looked for risk factors impacting sick calves, saying, “Those calves that got sick in the first 75 days were most likely to have a two-year-old dam for a mother. In fact, they were five times more likely to get sick if their dam was a two-year-old in the first 75 days.” 

Later illness was more likely to result in calves born to older cows. 

“We thought illness in calves before 75 days might have to do with lack of passive transfer in terms of colostrum in heifers,” he says. “Failure to receive colostrum puts calves at risk of pneumonia prior to 75 days of age.” 

  Rapid epidemics of sickness is often seen in calves that are between three and five months of age, Smith says, explaining, “These calves have lost their immunity all at the same time, leaving them more susceptible to disease.” 

“There are two patterns resulting from passive transfer of immunity, resulting in sporadic cases of disease in young calves and loss of immunity, resulting in larger outbreaks in calves that are 75 to 150 days of age,” he explains.

Environmental factors

Management practices, environmental conditions and more have implications on pneumonia in calves. 

“There was a positive association with the use of estrus cycle synchronization programs in cattle and pneumonia,” Smith says. “Producers who reported problems with pneumonia in calves also were more likely to say they use estrus cycle synchronization.”

Further, Smith adds, “They were also more likely to say they introduced calves from an outside source or that they offered supplemental feed to calves using creep feed.” 

Following the survey, Smith’s research team introduced a second study, randomly selecting control herds with less than half of one percent of calves affected by BRD and case herds, which treated more than five percent of calves treated for BRD.

Thirty control herds and 54 case herds were identified, and three factors were significantly associated with case herds, says Smith, including number of cows, whether intensive grazing was used and whether or not cows were synchronized for breeding. 

“The odds for a case herd increased with the size of the herd,” he says. “Herds that did intensive grazing were three times more likely to be a case herd, and the use of a synchronization program increased the odds that they had BRD was 4.5 times greater.” 

“We’re looking at pneumonia in calves prior to weaning as a childhood disease in cattle due to their age-related susceptibility because they’ve lost their colostrum and herd immunity,” Smith says. “Paradoxically, it seems to be associated with highly managed herds – larger herds following intensive grass and reproductive management.” 


To evaluate whether factors are important is determined by running calculations, which Smith’s team did. 

“In herds with 499 head with summer pneumonia, 71 percent of the risk is explained by herd size,” he says. 

Producer who do intensive grazing and have pneumonia can attribute 60 percent of the risk of the disease to intensive grazing. 

Finally, herds with BRD challenges that also utilize estrus synchronization can attribute 64 percent of their risk due to the synchronization strategy.

“Those are big numbers. They’re important,” Smith adds. “These three factors explain more than half of the occurrence of calf-hood BRD. Intensive management practices and larger herd size seem to be associated with BRD.” 

Explaining why

The reasons why intensive management and larger herds can lead to increased risk for BRD, according to Smith, is that the practices increase the opportunities for calves to be closer together.

“If we talk about a contagious pathogen, there are greater opportunities for one calf to share with another with these practices,” he explains. 

In particular, use of estrus synchronization can stress calves, also exposing them to dust and commingling them in pens for longer periods of time.

“As we tighten up the calving distribution and have more and more calves in a shorter period of time, they all become susceptible in a shorter window of time, leading to the sudden loss of herd immunity,” comments Smith. 

He continues, “The question for producers to ask themselves is, can we get the cost associated with summer pneumonia back by using estrus synchronization?”

Saige Albert is managing editor of the Wyoming Livestock Roundup. Send comments on this article to

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