In a herd of beef cattle with respiratory disease, which diagnostic test would most likely reveal a parasitic cause?

The Baermann exam for larvae in feces is a specialized technique that allows for the detection of certain parasitic infections, particularly those caused by nematodes, which may contribute to respiratory disease in cattle. This test is designed to isolate and identify the larvae of parasites that may be present in the gastrointestinal tract and can sometimes migrate to the lungs, leading to respiratory issues.

In cases where respiratory disease is suspected to have a parasitic origin, this method is particularly valuable because it directly focuses on detecting the larvae during a specific stage of their life cycle when they can migrate through tissues, potentially affecting the respiratory system.

Other diagnostic tests like the fecal smear examination may provide some insight into gastrointestinal parasites, but they are less effective for isolating larval forms that could be implicated in respiratory disease. A complete blood count can indicate the presence of infection or inflammation but does not specifically identify parasitic infections. Lastly, a chest X-ray is primarily used to visualize lung pathology and does not provide direct evidence of parasitic causes for the respiratory disease. Thus, the Baermann exam is the most relevant test for identifying parasitic involvement in respiratory conditions in cattle.