A coughing calf almost always points to one of three things: a respiratory infection, lungworm, or irritation from poor air quality in the housing environment. Respiratory disease is the single most common cause, especially in calves between three weeks and six months old. Figuring out which cause is at play depends on the calf’s age, temperature, and the pattern of the cough itself.
Bovine Respiratory Disease: The Most Likely Cause
Bovine respiratory disease (BRD) is responsible for more calf illness and death than any other condition. It typically starts with a virus that damages the lining of the airways, then bacteria that normally live harmlessly in the upper respiratory tract move into the lungs and cause pneumonia. The combination of viral damage and bacterial infection is what makes BRD so dangerous.
Several viruses can kick things off. Bovine respiratory syncytial virus (BRSV) and bovine parainfluenza-3 virus are two of the most frequently identified in young calves, particularly around weaning. Bovine herpes virus-1 causes heavy virus shedding and spreads rapidly through a group. Once any of these viruses weaken the airway defenses, bacteria like Mannheimia haemolytica and Pasteurella multocida take hold. These bacteria are already present in a healthy calf’s nose and throat. Stress from the viral infection, transport, weaning, or overcrowding gives them the opening to invade the lungs.
A calf with BRD will typically have a rectal temperature above 103.1°F (the normal range for cattle is 100.4 to 103.1°F). You’ll often see nasal discharge that progresses from clear to thick and cloudy, droopy ears, watery or crusty eyes, and reduced appetite. The cough may start as something you can only trigger by pinching the trachea, then progress to frequent spontaneous coughing as the disease worsens.
How to Score the Severity
The University of Wisconsin developed a simple calf respiratory scoring system that helps you decide whether a cough needs treatment. It grades four signs on a 0 to 3 scale:
- Cough: 0 is no cough, 1 is a single cough when induced, 2 is repeated induced coughs or occasional spontaneous coughing, and 3 is repeated spontaneous coughs.
- Nasal discharge: 0 is clear, 1 is a small amount of cloudy discharge from one nostril, 2 is cloudy discharge from both nostrils, and 3 is heavy, pus-like discharge from both sides.
- Eye score: 0 is normal, progressing to 3 for heavy discharge from both eyes.
- Ear score: 0 is normal, 1 is ear flicking or head shaking, 2 is a slight droop on one side, and 3 is a head tilt or both ears drooping.
A combined score of 5 or higher generally indicates the calf needs treatment. Catching BRD early, when the cough is still at a 1 or 2 and only one other sign is present, dramatically improves outcomes.
Lungworm Infection
If your calf has been on pasture, lungworm is a real possibility. Calves pick up the larvae by grazing contaminated grass. The larvae migrate through the gut wall, travel through the bloodstream, and end up in the lungs, where they mature into adult worms in the airways.
The coughing from lungworm tends to develop more gradually than viral pneumonia and persists longer. Infected calves show coughing, nasal discharge, rapid breathing, and labored abdominal breathing. Research comparing the two conditions found that BRSV infection produces more acute signs that resolve faster, while lungworm symptoms build slowly and linger. A fecal test can confirm the diagnosis by detecting larvae. Calves in their first grazing season are most vulnerable because they haven’t built any immunity yet.
Aspiration Pneumonia in Very Young Calves
If a calf develops coughing in the first few days of life, or shortly after being tube-fed, aspiration pneumonia should be high on the list. This happens when milk, colostrum, or electrolytes enter the windpipe instead of the esophagus. A misplaced esophageal feeding tube is one common cause. Calves weakened by a difficult birth or diarrhea may also have a poor swallow reflex, making it easy for fluids placed in the mouth to slip into the airway.
One clue that points to aspiration: only one lung may be affected. If the calf was lying on its side when the fluid entered, it tends to settle into the lower lung. Aspiration pneumonia can be severe and often responds poorly to standard antibiotic treatment because the lung tissue is damaged by the fluid itself, not just by bacteria.
Poor Air Quality and Housing Problems
Sometimes the cough isn’t caused by an infection at all. Dusty bedding, poor ventilation, and ammonia buildup in calf barns can irritate the airways enough to cause chronic coughing. Research from the University of Wisconsin found that calves exposed to ammonia levels above 4 parts per million (ppm) had a higher prevalence of lung lesions. The recommended target is below 5 ppm at calf nose level, which for a lying calf is right at the surface of the bedding.
This is an easy problem to miss because the calf may look otherwise healthy. If you crouch down to calf height in the pen and your eyes sting or you can smell ammonia, the levels are too high. Clean, dry bedding and proper ventilation that moves stale air out without creating drafts on the calves are the fix. Straw bedding works well for warmth but can get dusty. The key is keeping it dry and replacing it frequently enough to prevent ammonia from building up.
Why Some Calves Get Sick and Others Don’t
The biggest single factor in a young calf’s disease resistance is whether it absorbed enough antibodies from colostrum in the first hours of life. Calves are born with essentially no immune protection of their own. They depend entirely on antibodies absorbed from the dam’s first milk. If blood antibody levels fall below 10 g/L, the calf has what’s called failure of passive transfer, and its risk of respiratory disease climbs sharply. In one study of 225 beef calves across 45 herds, 19% had inadequate antibody levels.
Calves that didn’t get enough quality colostrum within the first 6 to 12 hours are more susceptible to every respiratory pathogen on this list. Stress compounds the problem. Mixing calves from different sources, transport, sudden weather changes, and overcrowding all suppress immune function and give bacteria their window to invade the lungs.
Treatment and What to Expect
BRD and bacterial pneumonia are treated with antibiotics, typically given as a single injection under the skin or into the muscle. Several long-acting options are available that provide therapeutic levels for days after a single dose, which reduces handling stress. Your veterinarian will choose the antibiotic based on the calf’s age, weight, and the severity of signs. Early treatment, before the calf stops eating and becomes visibly depressed, gives the best chance of full recovery.
Lungworm is treated with a dewormer rather than antibiotics. If the cough is environmental, no medication will fix it. You have to fix the housing.
For prevention, intranasal vaccines against BRSV and parainfluenza-3 can be given to very young calves. These vaccines are sprayed into the nose and stimulate local immunity in the airways, working even in the presence of maternal antibodies that would block injectable vaccines. Timing matters. Vaccination before the period of highest risk, typically before weaning or before mixing with new animals, gives the best protection.
What to Check Right Now
If your calf is coughing today, start with a rectal temperature. A reading above 103.1°F strongly suggests infection. Look at both nostrils for discharge and note the color. Check the ears for drooping and the eyes for discharge. Watch the calf’s breathing from a distance before approaching: is it faster than the other calves, and is the belly heaving with each breath?
A calf that is still eating, has a mild cough, clear nasal discharge, and a normal temperature may just need better ventilation or monitoring. A calf with a temperature over 104°F, cloudy discharge from both nostrils, droopy ears, and spontaneous coughing needs treatment that day. Pneumonia can progress from treatable to fatal in 24 to 48 hours in a young calf, so waiting to see if it improves on its own is a gamble with poor odds.