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Serious Threat to Calves

Mannheimia haemolytica, formerly known as Pasteurella, is the primary cause of BRD complex, including shipping fever and calf pneumonia. M. haemolytica is present in nearly 75% of all diagnosed cases of BRD, causing more death and economic loss than any other cattle disease.1

Severity and Transmission

M. haemolytica bacteria release leukotoxin, which attacks the calf’s immature defense system and is a major contributor to lung injury in shipping fever pneumonia. It’s also the bacteria most frequently isolated from pneumonic lungs in cattle and is often associated with acute cases of BRD.

M. haemolytica causes respiratory tract infections when the organism is inhaled and transferred into the lungs. Respiratory disease can compound when the bacteria is present simultaneously with other infectious pathogens—the severity of disease can depend on the degree of co-infection with associated viral agents such as IBR, PI3, BVD and BRSV.

Animals are more susceptible to infection when their natural defenses are compromised due to stress caused by weaning, handling, shipping, commingling or a change in environment. M. haemolytica is highly transmissible within a herd. The bacteria can be spread by direct contact or through feed and water that has been contaminated by nasal and oral discharges from infected cattle.

Signs of Pneumonia

M. haemolytica infections can develop and advance quickly. Clinical signs of pneumonia include:

  • Mild to profuse discharge from the nose and eyes
  • Coughing
  • High temperatures
  • Lesions on the muzzle and nostrils
  • Edema (fluid) in lower jaw and neck

Animals affected with respiratory disease have difficulty breathing and may be unable to eat or drink. Animals with severe BRD may develop substantial lung lesions that may result in death of the animal. Reduced weight gain is a common and costly effect of BRD. Though calves can survive infection, they may suffer from irreversible lung damage that is often associated with poor performance.

  1. Richey EJ. Pasteurella disease in beef cattle. Institute of Food and Agricultural Sciences Publication VM-63, University of Florida. Available at: Accessed 3/21/12.
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