Despite report of decreased effectiveness of BRD drug therapies, cow/calf producers should focus on BRD prevention such as vaccination and good nutrition.
RESULTS from a three-year study at Kansas State University identified an increasing drug resistance to one of the primary pathogens that causes bovine respiratory disease (BRD).
Brian Lubbers, assistant professor in the Kansas State Veterinary Diagnostic Lab, reported that a high percentage of Mannheimia haemolytica bacteria recovered from cattle lungs were resistant to several drugs that are typically used to treat that pathogen (Feedstuffs, July 1).
"Many of these bacteria are resistant to not one but almost all of the antibiotics that we use to treat BRD in cattle," Lubbers said.
Because there are a limited number of antimicrobial drugs that can be used for treatment of these pathogens, multi-drug resistance poses a significant threat to the livestock industry.
"This Kansas State University study underscores the importance of pneumonia prevention," said Dr. John M. Davidson, professional services veterinarian with Novartis Animal Health.
"M. haemolytica, formerly known as Pasteurella haemolytica, has been around since the turn of the (20th) century," Davidson added. "It's the leading bacterial cause of BRD complex in cattle today. BRD complex continues to be the number-one cause of death among calves. Data from the most recent National Animal Health Monitoring Service report shows that 29% of all calf deaths are caused by BRD."
Davidson said the costs associated with calves that are treated for BRD and survive are high — ranging from $40 to $300 per calf when medicine, labor and reduced carcass value are taken into account.
"We know that through prevention, we can specifically target M. haemolytica at a much lower cost than the producer ultimately bears by bringing high-risk cattle that are not prepared for the feedlot to the marketplace," Davidson said.
"We encourage veterinarians and producers to consider the value of vaccination and the benefit to that calf's well-being in preventing M. haemolytica in the first place and how that is far superior to relying on mass medication after the stress and onset of disease."
To be most effective, Davidson said producers should vaccinate calves prior to stressful periods.
"To get the maximum response from vaccines, it's important that we don't overwhelm the animal's immune system," Davidson said. "In the summertime, this means avoiding vaccinating cattle at extremes in heat index."
Vaccinating in the morningis advantageous in hot climates or periods of high humidity.
Davidson encouraged producers to focus on key management and preconditioning practices that help minimize the incidences and effects of pneumonia. Calves also should be vaccinated for viral diseases that contribute to BRD, including bovine virus diarrhea, bovine respiratory syncytial virus, infectious bovine rhinotracheitis and parainfluenza-3.
"Good nutrition also strengthens the calf's immune response. Well-nourished calves have the propensity to better avoid becoming ill in the first place," Davidson said.
BVD virus strain
The U.S. Department of Agriculture has issued a Veterinary Biological License for Viralign 6, the first combination modified-live virus vaccine to provide targeted protection against bovine viral diarrhea (BVD) virus 1b — the most predominant BVD virus strain in the U.S.
Marketed by Elanco, the vaccine also provides protection against BVD viral strains 1a and 2, bovine respiratory syncytial virus, infectious bovine rhinotracheitis virus and parainfluenza-3 virus.
"Until now, veterinarians and producers have relied on combination vaccines with BVD 1a and 2 to cross-protect against what is now the most predominant strain: 1b," Dr. Carl Guthrie, director of Elanco beef technical services, said.
This first-of-its-kind vaccine enables low-volume, subcutaneous administration in cattle five months of age or older, Elanco said.
"Even though producers have vaccinated for the BVD virus for years, research shows that its incidence has not gone down, and 1b has replaced 1a as the most predominant BVD strain," Guthrie said. "The good news is that ongoing vaccination programs appear to have decreased the predominance of 1a in the U.S., but it also suggests that current modified-live 1a vaccines may not adequately protect calves from 1b infections."
The BVD virus is an RNA virus, which means it is more susceptible to mutation, Elanco said. That's why researchers monitor BVD viral strains to identify changes in predominance.
In fact, a USDA Agricultural Research Service analysis of diagnostic samples shows that there has been a shift in predominance of BVD viral strains in the U.S. In 1988, subtype 1a was predominant at 51%, but 20 years later, 1a ranked third at 18%, while subtype 1b had increased in predominance from 41% to 61%. At the same time that 1a was decreasing, the overall incidence of BVD virus did not decline, Elanco said.
"One of the primary sources of the BVD virus is exposure to persistently infected (PI) animals — cattle that are few in number but shed large amounts of the virus throughout their lives," Elanco senior technical consultant Brad Williams said. "Comprehensive research involving 21,743 head shows that 78% of PI cattle were infected with 1b."
According to another study, Elanco noted that calves exposed to a PI calf are 43% more likely to require treatment for BRD. Also, due to the immune-suppressing nature of BVD, cattle might not show signs of infection even though they suffer from subclinical respiratory and other profit-robbing diseases.