Thoracic ultrasound: How do we use it?

By Dr. Dave Renaud, ACER Consulting Ltd.

Ultrasound has long been an imaging technique used on dairy farms by veterinarians to determine the pregnancy status of an animal. However, this technology is now emerging as a diagnostic and monitoring tool used to help to detect respiratory disease in dairy calves. 

Why use thoracic ultrasound?

Thoracic ultrasound is the most accurate tool available to diagnose respiratory disease in calves. It involves taking an ultrasound probe and running it between the ribs of an animal to identify areas of consolidation in the lung, which are areas where air is not readily passing through.

Lung consolidation occurs when there is an infection in the lung that causes white blood cells, dead cells, and debris to fill the small airways in the lung, preventing air from passing through. Lung consolidation is one of the first changes to the lungs when disease is present and often calves with lung consolidation do not show any clinical signs of disease. Thoracic ultrasound is a tool that helps indicate where disease is occurring and provides an idea of when producers can intervene.

How often is lung consolidation found and what are the consequences?

Several recent studies have shown just how common lung consolidation really is. A study in Ontario that assessed calves weekly with ultrasound in the preweaning period found that 57 per cent of calves had an area of lung consolidation. Comparatively, in Ohio, 73 per cent of calves had lung consolidation when assessed on a weekly basis in the preweaning period.

These studies also identified several consequences of having lung consolidation. Specifically, calves with lung consolidation had a 120 g/d reduction in growth, an increased risk of being removed from the herd prior to first calving, a lower conception rate at first insemination as a heifer, a reduced chance of becoming pregnant, and have a 525 kg reduction in first lactation milk production. Cumulatively, it is estimated to cost approximately $400 per calf with lung consolidation.

Clearly, combining the high rate of lung consolidation with the significant consequences and long-term economic impact means preventing respiratory disease in calves should be high priority for producers.

When and how should thoracic ultrasound be used?

In a research setting, lung ultrasound can be used on a weekly basis, however, on-farm use needs to be a bit more pragmatic. By using ultrasound strategically with the herd veterinary team, producers can better understand how the calves and the individual producer’s management works to prevent respiratory disease.

Ultrasound can help determine how effectively producers and their calf management team are identifying respiratory disease based on clinical symptoms, such as coughing, where calves are evaluated at the start of treatment to determine the severity of lung consolidation. It could also be used to determine the impact of treatments provided for respiratory disease, where calves are evaluated for lung consolidation seven days after treatment to ensure resolution. Finally, it can be used to evaluate calf barn performance and the farm’s prevention program for respiratory disease, where calves are assessed at set times, like weaning, to evaluate trends over time.

How can lung consolidation be prevented?

There are four critical areas to consider when aiming to prevent respiratory disease:

1. Colostrum management: calves with failed transfer of passive immunity are 1.75 times more likely to have respiratory disease.
2. Milk nutrition: feeding at least eight litres of milk or milk replacer each day in the preweaning period has been shown to reduce respiratory disease.
3. Housing: one of the most critical areas is ensuring that calves are housed in a well-ventilated area where air is being delivered without a draft. In addition, providing enough bedding for calves to nest in can help prevent respiratory disease in the winter.
4. Vaccination: the use of intranasal vaccines in the preweaning period has been found to reduce lung consolidation.

Take home messages

Thoracic lung ultrasound is a validated method to detect respiratory disease early after its onset. Veterinarians can use lung ultrasound practically on the farm to better understand how effectively the calf management team is treating, diagnosing, and preventing respiratory disease.

Finally, lung consolidation can be prevented through excellent colostrum management, feeding a high plane of nutrition, ensuring the calf barn is well-ventilated, and strategically using intranasal vaccines. Producers should work with their veterinarian to determine how lung ultrasound could work on their farm.

This project was funded by the Canadian Agriculture Partnership, a five-year federal-provincial-territorial initiative.