Pneumonia in pre-weaned beef calves continues to vex cattle producers and veterinarians every summer. Because it occurs in well-vaccinated and managed herds as well as in minimally managed herds, and because of its unpredictable nature, summer pneumonia can be frustrating.
Veterinarians have some tools at their disposal when it’s warranted to investigate these outbreaks more closely. It’s a good idea for cattle producers to know how some of those tools work and whether they make sense for their situation.
In particular, the tools we’re talking about are diagnostic techniques to identify bacteria and viruses that may be contributing to a summer pneumonia outbreak. Veterinarians have close connections with veterinary diagnostic labs, such as the SDSU ADRDL (contact info below), that can employ these techniques.
Why take samples?
Why wouldn’t one want to know exactly which germs are involved in a summer pneumonia outbreak? In a strictly practical sense, it might not matter. Many bovine pneumonia outbreaks in general are bacterial in nature, with Mannheimia hemolytica, Histophilus somni, or Mycoplasma bovis common culprits. The broad-spectrum antibiotics commonly used to treat pneumonia are typically effective against all of them. This often makes identifying the germ to guide treatment a moot point.
But sometimes treatments don’t work, or pneumonia outbreaks due to viruses occur. In these cases, germ identification can help guide future treatments or vaccination programs. The first step in the diagnostic process therefore, should be a good conversation with the herd veterinarian about what knowledge and advantages should be expected from doing the diagnostics.
What animals to sample
We know that pneumonia in cattle is a complex state of affairs that involves viruses, bacteria, and external factors such as weather and stress. Bacteria that are commonly associated with severe pneumonia can be found in the nasal passages of normal, healthy calves, causing no ill effects. These calves have healthy mechanisms (called pulmonary clearance) that keep these bacteria confined to the nose. When viruses such as IBR or BVD enter the picture, or external stresses knock down the immune system, pulmonary clearance mechanisms fail, allowing the bacteria access to the fertile ground of the lower lung. Inflammation, fever, and difficult breathing are the results.
Knowing this, the best sample for identification of pneumonia pathogens is the lung itself. Lung tissue can be sent to the diagnostic lab for bacterial culture, viral identification techniques or PCR tests which can identify germs present in the lungs.
However, using lung tissue for pathogen identification has some obvious downsides. First, lung tissue is only available from dead calves! Many summer pneumonia outbreaks occur with no death losses. Additionally, by the time pneumonia has progressed to a fatal condition, the triggers (viruses) that precipitated the outbreak are sometimes no longer present in the lung. Another pitfall occurs when calves have been treated with antibiotics. In those cases, antibiotics in the calf’s system will have killed off bacteria in the organs even if they were not successful in making the calf better.
Getting meaningful diagnostic results means sending in samples that are in good condition. Calves that have been dead for more than a few hours in hot summer weather are poor candidates for diagnostics due to decomposition of the lung tissue. Samples should be put on ice and kept cool all the way from the pasture to their arrival at the diagnostic lab.
Your herd veterinarian is the best source of information about post-mortem sampling. They should be enlisted to take the samples from calves since they can perform a complete post-mortem examination at the same time. What outwardly may seem like pneumonia, sometimes isn’t; that’s why a skilled look at the entire body is also important.
What if taking post-mortem samples isn’t possible or feasible? The second part of this article will discuss the use of nasal swabs in summer pneumonia diagnostics.