Weaning and shipping may be just the opening bacteria are waiting for — and when bacteria have the advantage, the results can be costly, or even deadly, for calves. Pasteurella bacteria are normally found in the upper respiratory tract of cattle. They wait for the animal to become stressed and more vulnerable to infection before they are able to invade the animal’s lungs.

Pasteurella pneumonia occurs when the animal’s normal defenses are compromised, often involving environmental or nutritional stress,” says Bruce Nosky, DVM, Merial Veterinary Services. “The stress that cattle experience during weaning, commingling and shipping can create ideal conditions for these bacteria to reproduce and cause damage that leads to pneumonia.”

When the animal’s defenses are compromised, such as during weaning or from a viral infection, the bacteria are able to get into the lower respiratory tract, reproduce rapidly and spread throughout the lungs. The severity of the disease depends upon which Pasteurella organisms are involved and the nature of the other infections present.

“At first, clinical signs of Pasteurella pneumonia are difficult to detect, as calves will likely exhibit slight depression and lack of interest in eating,” Nosky says. “However, as the disease progresses, these signs worsen quickly and can result in a high fever, refusal to eat, labored breathing, irreversible lung damage and possibly death.”

Pneumonia develops rapidly
He adds that Pasteurella pneumonia develops very rapidly. And, if the initial signs are missed, the chances for the calf to recover, or survive, decline. “Pneumonia is difficult to diagnose and treat because the early signs, such as lack of interest in feed, can easily be overlooked,” Nosky says. “This is why it is important for both the health and profitability of cattle for producers to vaccinate calves for Pasteurella to help them fight this costly disease.”

Mannheimia haemolytica and Pasteurella multocida are the two major pathogens associated with Pasteurella pneumonia. These bacteria have been documented to be present in 75% of bovine respiratory disease (BRD) cases. For this reason,  Nosky recommends producers use a vaccine that helps protect calves against both.

“Not all vaccines are effective against both Mannheimia haemolytica and Pasteurella multocida,” he says. “This is especially important because research suggests that the incidence of P. multocida is increasing.” As producers prepare for fall weaning, Nosky recommends they work with their veterinarian to develop a plan to help calves fight the stress of weaning.

“Helping calves fight this disease starts by keeping the resistance level of the animal above the disease challenge,” he says. “Producers should work with their veterinarian to implement a calf preconditioning program that includes a Pasteurella vaccine to help prevent both major causes of Pasteurella pneumonia. This can help calves prepare to weather the BRD storm this fall.”