When a calf develops pneumonia, the immediate priority is treating the animal. The investigation, however, should extend beyond the individual case. What organisms are involved? Where might they be coming from? Are the same patterns appearing in other calves? And what can the findings tell the farm about preventing the next case?
Answering those questions takes more than one test. Dr. Curt Vlietstra, senior professional services veterinarian with Boehringer Ingelheim and the most recent guest on “The Bovine Vet Podcast”, encourages veterinarians to approach respiratory diagnostics as a way to build a broader picture of disease on the farm.
The goal is to understand what is happening in the affected calf while gathering information that can guide herd-level decisions.
Choosing the Right Respiratory Sample
Different collection methods reach different parts of the respiratory tract, and the results need to be interpreted accordingly. Vlietstra describes several options:
- Nasal swabs: One of the simplest and most accessible sampling methods, although the nose is exposed to organisms from the surrounding environment. “The nose of any animal is going to be dirty. There’s going to be bugs there, but it’s still better than doing nothing,” Vlietstra says.
- Deep nasopharyngeal swabs: A longer swab reaches the back of the throat to identify organisms that have moved beyond the nasal passages. This provides information about the upper respiratory tract, but does not establish what is present in the lungs.
- Lower respiratory tract samples: Transtracheal washes and bronchoalveolar lavage collect material from the lungs, providing a more direct assessment of organisms present in the lower airways.
The choice of sample depends on the diagnostic question, the condition of the calf and the resources available. A positive result from an upper respiratory sample does not necessarily tell the same story as one from a lower respiratory sample.
Timing is also important. When possible, samples should be collected before antibiotic treatment begins. Treatment can bias diagnostic results, making it harder to determine which organisms were present before therapy.
Lung ultrasound can help identify calves with lesions that may not be clinically obvious. Those calves can then be considered for additional sampling before treatment begins. Ultrasound identifies abnormal lung tissue, but it does not identify the organism responsible.
Postmortem Diagnostics Can Add Important Evidence
Live-animal sampling is only one part of the investigation. Calves that die from respiratory disease can also provide valuable diagnostic information, even after multiple treatments.
“Doing a full diagnostic workup on those dead calves is still beneficial,” Vlietstra says.
A laboratory may not always recover the organism responsible for the infection, particularly after treatment. Examination of the tissues can still reveal changes consistent with a particular pathogen or disease process. Considered alongside the clinical history and other test results, those findings can help with interpretation of the case even when an organism cannot be isolated.
Combine Diagnostic Findings to Understand the Herd
Vlietstra compares respiratory diagnostics to mastitis investigations:
“I think of it almost like mastitis, where you can take a culture from the milk to know what bugs get into the milk. And then you can take a culture from the bedding to know what bugs are in the environment and then obviously take a milk sample from the cows that have clinical mastitis to know which of those bugs are making it from the environment into the milk that are also impacting the cows.”
The same investigative approach can help build a picture of respiratory disease. Findings from affected calves can be considered alongside information about their environment and the patterns seen in other animals. Looking across those sources provides more context than interpreting an individual sample in isolation.
Detecting an organism does not automatically establish that it is responsible for the clinical disease. However, as Vlietstra explains: “The only way to prove an infection is to find a bug to associate with it.”
Identifying an organism is only part of the investigation. Viruses and bacteria can contribute to respiratory disease in different ways. Some viruses damage lung tissue or suppress immune function, making calves more susceptible to secondary bacterial infections. Understanding those interactions allows the interpretation of diagnostic findings in the context of the disease process.
The challenge is to determine which findings are relevant to the respiratory disease pattern on a particular farm.
Vlietstra says farms that use diagnostics most effectively have a routine for ongoing testing and a plan for investigating more thoroughly when respiratory disease increases.
Routine testing establishes a baseline. When disease rises, you can compare current findings with what is normally seen on the farm and determine where additional sampling may be useful. Without that reference point, it can be difficult to know whether a new finding represents a meaningful change.
Use Diagnostic Results to Guide Prevention
A rise in respiratory disease should prompt a look beyond the calves currently receiving treatment. As Vlietstra puts it: “In some ways, the sick calf isn’t the one that you should be worried about. It’s the next calf that’s going to get sick.”
That perspective shifts the focus from responding to individual cases to identifying what could put other calves at risk.
A farm’s historical records can help establish normal respiratory disease incidence, including the proportion of calves with measurable lung lesions or the number requiring treatment. Vlietstra emphasizes the value of consistent measurement: “If you measure it, you can monitor it. And then if you monitor it, you can use it to make the decisions.”
When disease incidence numbers change, records and benchmarks provide a reference point for deciding whether a deeper investigation is warranted. The same approach can be applied to management factors such as passive transfer, colostrum quality, bedding and hygiene. Establishing benchmarks before disease increases makes it easier to identify what may have changed.
Diagnostic findings can also inform vaccination and treatment protocols. Vaccines are useful tools, but they do not cover every pathogen. Understanding which organisms are involved can help veterinarians evaluate whether the current vaccination program is appropriate, whether vaccine timing should change or whether treatment protocols need to be reassessed.
Those findings should also be considered alongside management conditions. Vlietstra points to moisture, seasonal temperature fluctuations and bedding as potential contributors to respiratory challenges. When disease increases, these factors deserve attention alongside laboratory results.
The value of diagnostics, he says, also depends on how producers view the expense.
“Diagnostics aren’t free,” Vlietstra says. “So to have a plan and to kind of shift your mindset from this is a cost to this is just another input for prevention and optimizing performance is important.”
For veterinarians, that investment can help identify changes that reduce future cases, improve treatment decisions and support the productivity of replacement animals. A well-designed diagnostic plan connects findings from individual calves with herd records and management conditions. The resulting picture gives veterinarians a stronger basis for deciding what to investigate and how to reduce the risk to the next calf.
To hear more from Dr. Vlietstra on pneumonia and respiratory disease management, tune in to the latest episode of “The Bovine Vet Podcast":
