Bovine respiratory disease (BRD) remains one of the most common and costly health challenges in preweaned dairy calves. The challenge is that many cases develop long before calves show visible symptoms.
“By the time calves show obvious clinical signs of respiratory disease, lung damage may already be present,” says Aerica Bjurstrom, regional dairy educator at the University of Wisconsin-Madison. “That’s why tools that help us detect pneumonia earlier can make a big difference in calf health and long-term performance.”
Traditional diagnosis relies on symptoms such as coughing, nasal discharge, or elevated temperature. But these signs often appear late in the disease process. In many cases, calves may look completely healthy while still carrying lung infections.
This form of illness, known as subclinical pneumonia, can reduce growth, feed efficiency and even future milk production.
“The lungs can really act as an indicator organ,” Bjurstrom explains. “Respiratory disease often reflects larger management challenges, such as poor colostrum intake, nutrition issues, or environmental stress.”
The Hidden Pneumonia Problem
Research has shown that pneumonia often develops days before visible symptoms appear.
“Ultrasound allows us to see what’s happening inside the lung tissue, even when the calf looks normal from the outside,” Bjurstrom says. “In many cases, pneumonia can be present for days before any clinical signs appear.”
Studies suggest that 50% to 80% of pneumonia cases may remain subclinical for 7 to 14 days before producers notice symptoms. That delay can allow lung damage to progress before treatment begins.
“Sometimes calves with severe pneumonia don’t show obvious symptoms,” Bjurstrom says. “But an ultrasound exam can reveal lung lesions that tell us the disease is already present.”
How Lung Ultrasound Works
Lung ultrasonography allows veterinarians to examine calf lungs in real time using portable ultrasound equipment.
A normal lung appears air-filled on the scan and produces horizontal white lines that move with each breath. These lines indicate healthy lung tissue.
Changes in the image can reveal early disease.
“Comet tails are bright vertical lines that extend down from the lung surface,” Bjurstrom says. “A few may be normal, but severe or diffuse comet tailing can suggest interstitial disease caused by fluid or inflammation within the lung.”
More advanced disease appears as lung consolidation, where portions of the lung fill with inflammatory material instead of air. On ultrasound, these areas appear as solid gray regions.
Veterinarians often use a 0 to 5 lung scoring system to evaluate severity.
“This scoring system helps identify disease before calves begin coughing or showing nasal discharge,” Bjurstrom says. “Early detection allows for earlier treatment and better outcomes.”
Why Early Detection Matters
Even when calves show no visible symptoms, lung damage can affect their long-term performance.
In one study of more than 600 Holstein heifers, calves with lung consolidation detected at weaning were less likely to become pregnant and more likely to leave the herd before first calving.
Another study found calves with significant lung lesions in the first eight weeks of life produced 1,155 pounds less milk during their first lactation.
“These findings highlight why early detection matters,” Bjurstrom says. “Subclinical disease can still influence growth, reproduction, and milk production later in life.”
Improving Treatment Outcomes
Early detection can also make treatment more effective.
“When pneumonia is caught earlier, treatment tends to work better,” Bjurstrom explains. “We’re able to intervene before the disease becomes severe and causes permanent lung damage.”
Ultrasound can also help veterinarians monitor recovery.
“That monitoring aspect is important,” she says. “It helps ensure calves are improving and reduces unnecessary retreatment.”
A Management Tool for Farms
Beyond diagnosis, lung ultrasound is increasingly used as a herd management tool.
“Ultrasound gives producers objective information about lung health,” Bjurstrom says. “That can help guide decisions about treatment, culling, or adjusting weaning timing for calves that may need more time to recover.”
Regular scanning can also reveal herd-level trends tied to management practices.
“When used consistently, ultrasound becomes a benchmarking tool,” Bjurstrom says. “It can help farms evaluate colostrum programs, ventilation, sanitation, and other factors that influence calf health.”
A Growing Tool in Calf Health Programs
Portable ultrasound units have become more accessible and easier to use, making them more common in calf health programs. With proper training, scanning a calf’s lungs typically takes less than a minute.
“The equipment requires an initial investment, but the information it provides can be incredibly valuable,” Bjurstrom says. “Earlier detection can lead to better management decisions, improved calf growth, and fewer losses.”
As dairy farms continue adopting more data-driven management practices, lung ultrasound is giving producers a new way to detect disease sooner and protect the long-term potential of their calves.
“Lung ultrasound helps us move beyond waiting for visible symptoms,” Bjurstrom says. “It allows producers and veterinarians to identify problems earlier and take action before long-term damage occurs.”
