LINCOLN, Neb — Wildfires burning in western and central Nebraska are part of a broader trend of increasing wildfire frequency and magnitude across the western United States, and the fallout can extend beyond burned pastures and damaged infrastructure. In addition to immediate losses to beef production and rural communities, wildfire smoke may pose risks to both human and animal health, leaving producers to watch calves closely in the weeks and months after a fire.

Wildfire smoke is produced when biomass burns, generating carbon dioxide and water vapor along with ash made up of inorganic compounds. Of particular concern is ultrafine particulate matter smaller than 2.5 micrometers, which can travel deep into lung alveoli and enter the bloodstream. In humans, these particles have been associated with inflammation and oxidative stress.

Research on wildfire smoke exposure in cattle is limited, but a study by Ranches and others (2026) involving a small group of Simmental × Jersey calves found increased concentrations of cortisol, an indicator of stress, after exposure to smoke from a wildfire about 10 miles from the study site. The same study reported elevated ceruloplasmin, a marker of systemic inflammation, following the wildfire event. Antibodies, including IgM and IgA, were also increased, suggesting activation of the immune system.

Physiological stress and inflammation can hurt cattle performance and immune function, potentially making calves more susceptible to respiratory pathogens. In bovine respiratory disease, opportunistic bacterial pathogens such as Mannheimia haemolytica, Pasteurella multocida, Histophilus somni and Mycoplasma bovis are normally present at low levels in healthy calves. But when viral infection or physiological stress suppresses immune function, these bacteria can multiply in the respiratory tract, leading to illness, reduced performance and, in some cases, death.

Because stressors such as wildfire smoke may increase disease susceptibility, producers are urged to monitor calves for early signs of illness. One approach is the D.A.R.T. method:

Depression: Watch posture and behavior. Droopy ears or head carriage, lethargy, more time spent lying down and separation from pasture mates can signal illness. Because cattle tend to hide sickness, subtle changes may be easier to spot after calves become accustomed to a person’s presence.

Appetite: Reduced appetite at the feed bunk or during nursing can indicate a health challenge. On pasture, reduced gut fill compared with herdmates can also suggest decreased intake.

Respiration: Healthy cattle typically take 10 to 30 breaths per minute. An increased respiratory rate, shallow breathing or abnormal sounds such as coughing or raspy breathing may indicate respiratory disease. Nasal discharge or excessive eye secretions may also accompany illness.

Temperature: Rectal temperatures of about 103.5 to 104 degrees or higher can indicate fever and warrant further attention.

Early detection and treatment can improve the likelihood of recovery and help reduce performance losses tied to respiratory disease. Producers are encouraged to remain vigilant in the weeks and months after smoke exposure to help limit adverse health outcomes.