Bovine respiratory disease, or BRD, is a complex of lung infections that stands as the single largest cause of sickness and death in feedlot cattle. It accounts for 60% to 90% of all illness and death in feedlots and costs the American beef industry an estimated $800 to $900 million every year in lost production and veterinary expenses. Often called “shipping fever,” BRD typically strikes when stress weakens a calf’s respiratory defenses, allowing viruses and bacteria to overwhelm the lungs.
How BRD Develops in the Lungs
BRD is not caused by a single germ. It’s the result of a chain reaction: stress suppresses the immune system, a virus damages the airway lining, and bacteria that normally live harmlessly in the upper respiratory tract seize the opportunity to invade the lungs. While single-pathogen infections can trigger an outbreak, co-infections involving a primary virus followed by secondary bacterial colonization are the more common pattern.
The viruses involved include bovine viral diarrhea virus (BVDV), bovine respiratory syncytial virus (BRSV), bovine herpesvirus 1, and parainfluenza 3 virus. Each attacks the respiratory tract in slightly different ways, but the end result is the same: they erode or degrade the protective mucous membranes lining the airways, killing epithelial cells and creating openings for bacteria to move deeper into the lungs.
The bacteria that take advantage of this damage are primarily Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis. These organisms normally live in the nose and throat without causing harm. Once they reach the lower lungs, though, they trigger severe pneumonia. In one study of feedlot cattle that died from BRD, Mannheimia species were present in 91% of cases, Mycoplasma bovis in 63%, and Histophilus somni in 57%.
What Triggers an Outbreak
Stress is the spark that sets BRD in motion. The biggest risk factor is the combination of transport and commingling, where calves are shipped to a new facility and mixed with unfamiliar animals. Cases typically peak in the first weeks after arrival. This is why the disease earned the nickname “shipping fever.”
The stressors are often layered on top of each other. A calf may be weaned from its mother, loaded onto a truck, hauled for hours, run through an auction, then placed in a pen with dozens of calves from different herds, all within a matter of days. Research has shown that additive stressors like weaning combined with transport produce greater inflammatory responses in the lungs and increased mortality during experimental infections. Shipping stress alone triggers heightened inflammatory immune responses in the airway lining, which paradoxically can make the lungs more vulnerable rather than more protected.
Other contributing factors include dust, temperature swings, poor ventilation, overcrowding, and inadequate nutrition. Any condition that taxes the animal’s body makes it harder for the immune system to keep respiratory pathogens in check.
Signs to Watch For
Cattle with BRD show a recognizable cluster of symptoms. The earliest and most reliable indicator is fever, with a rectal temperature above 39.5°C (about 103°F). Along with the fever comes lethargy, loss of appetite, and a general look of depression: drooping ears, dull eyes, and a lowered head.
Respiratory signs follow quickly. Nasal discharge, which may start clear and turn thick or colored, is common. Coughing, rapid breathing, and visible effort when breathing all point to lung involvement. In severe cases, cattle resort to open-mouthed breathing, a sign of serious respiratory distress. Ocular discharge, or “weepy eyes,” often accompanies the nasal symptoms.
Behavioral changes can be subtle but telling. Sick calves tend to sleep more, interact less with pen mates, and drink more slowly. That slower drinking speed has been identified as one of the more distinct feeding traits in calves with clinical BRD. These behavioral shifts sometimes appear before the more obvious respiratory signs, making close observation in the first weeks after arrival especially valuable.
How BRD Is Diagnosed
Traditionally, pen riders identify sick cattle based on visual observation: the animal that’s standing apart from the group, not eating, breathing hard, or showing nasal discharge. A rectal temperature reading then confirms or rules out fever. This approach catches many cases but misses others, particularly subclinical infections where lung damage is occurring without obvious outward signs.
Thoracic ultrasound has emerged as a more precise diagnostic tool. It provides real-time images of the lungs and can detect consolidations (areas where lung tissue has become solid and non-functional), fluid around the lungs, and other abnormalities. Compared to traditional methods like listening to the chest with a stethoscope, ultrasound offers superior accuracy in detecting both subclinical and advanced respiratory conditions. It also has prognostic value: the more lung consolidation visible on ultrasound, the higher the risk of relapse, reduced growth, and death.
Treatment
Because the disease-causing damage comes from bacterial infection in the lungs, antibiotics are the primary treatment. The goal is to target the main bacterial players: Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni. Several classes of antibiotics are approved for BRD treatment in the United States, including macrolides, fluoroquinolones, phenicols, and beta-lactams.
Early treatment matters. Cattle identified and treated at the first signs of illness respond far better than those treated after the infection has been established for days. Animals that fail to respond to an initial course of antibiotics may need retreatment with a different class, but each successive treatment tends to be less effective. Chronically infected cattle often suffer permanent lung damage that reduces their growth performance for the rest of their lives, even if they survive.
A growing concern is antimicrobial resistance. Studies of feedlot cattle that died from BRD have found that many of the bacterial pathogens involved carry resistance to multiple drug classes, making treatment selection increasingly important.
Prevention and Preconditioning
The most effective way to reduce BRD losses is to prepare calves before they face the stresses of transport and commingling. This preparation, called preconditioning, involves vaccinating, weaning, and acclimating calves to feed bunks and water troughs while they’re still on the ranch of origin, weeks before they’re shipped.
Vaccination timing plays a major role in how well calves are protected. The cow-calf phase, before any shipping occurs, is the most favorable window because it gives the immune system time to build protection before calves encounter BRD pathogens at a new facility. For calves that arrive at a stocker or feedlot operation without prior vaccination, delaying vaccination 14 to 30 days after arrival has been shown to improve health and performance outcomes in high-risk animals. Vaccinating on arrival day, when the animal’s immune system is already stressed, can be counterproductive.
Vaccine handling also matters more than many producers realize. Vaccines containing gram-negative bacteria need to be stored at proper temperatures, kept out of direct sunlight, and not shaken excessively. Rough handling can rupture bacterial cells in the vaccine and release endotoxins, which are compounds that trigger fever and inflammation. Giving multiple endotoxin-containing vaccines at the same time, a practice known as endotoxin stacking, can produce toxic reactions severe enough to kill an animal. Sick cattle or those experiencing heat stress should not receive these vaccines.
Beyond vaccination, practical management steps reduce BRD risk: minimizing the number of sources cattle are purchased from, reducing transit time, providing clean water and quality feed immediately upon arrival, and ensuring adequate pen space and ventilation. None of these measures eliminates BRD entirely, but together they substantially lower the odds of an outbreak.
Long-Term Impact on Performance
Even cattle that survive BRD pay a lasting price. The approximately 0.64% to 0.74% of cattle on feed in North America that die from BRD represent only the most visible loss. Animals treated for BRD gain weight more slowly, convert feed less efficiently, and often produce lower-quality carcasses at slaughter compared to pen mates that stayed healthy. Ultrasound studies confirm the reason: consolidated lung tissue doesn’t recover. A calf that loses 20% or 30% of its functional lung capacity will struggle to keep up with healthy animals for the rest of its feeding period, even if it shows no further clinical signs of illness.