A syndrome rather than a single disease, BRD often has multiple causative factors and pathogens.
By Dr. Jim Sears, Veterinary Technical Services, Bayer Animal Health
Replacement heifer calves represent the future of your dairy herd. One of the significant threats to their health and productivity is BRD, or Bovine Respiratory Disease. This article will address some items to consider when BRD occurs in your calves.
BRD is really a syndrome rather than a single disease. Most scientific journals refer to it as BRDC, or Bovine Respiratory Disease Complex, to convey that it often has multiple causative factors and pathogens. The time-honored “formula” (Stress + Viruses + Bacteria = BRD) still provides an accurate description of our overall understanding of this syndrome. After some type of stress, often complicated or initiated by a viral infection, the immune system of the calf is weakened sufficiently that a bacterial infection then takes hold in the lungs.
Where do the bacteria come from? Basically they are present in a dormant form in nearly all normal cattle. The calf typically becomes infected immediately after birth through the process of suckling the dam. The bacteria tend to stay dormant in the calf for weeks or months and become a problem when / if the immune system becomes weakened.
There are four bacterial pathogens most often associated with BRD: Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis. Each of them can cause a slightly different clinical syndrome, but there are some important commonalities:
· Once a bacterial infection takes hold, it can progress very rapidly. Calves can go from clinically normal to severely diseased or even dead within one to two days.
· If a bacterial infection goes unchecked, it can result in permanent lung damage, even if the calf returns to apparent normal health. Mycoplasma bovis, for example, is notorious for causing mild disease initially and advancing slowly but resulting eventually in severe and permanent lung damage.
· The more advanced an infection is before effective therapy is initiated, the more difficult the response and the more likely permanent lung damage or even death becomes. Early detection and effective treatment is essential. Consider these items:
Evaluate calves between milk feedings. Many calves with BRD will continue to drink until the disease becomes severe.
Evaluate the entire clinical appearance; not just rectal temperature. Some calves can be clinically ill but have a normal or slightly elevated rectal temperature. Routinely evaluate calves for such things as depression, cough, nasal or ocular discharge, ear droop, head tilt, head shaking, and ear scratching, to name a few.
Select an antibiotic that is labeled for BRD and follow the label. An ideal antibiotic is one that quickly achieves therapeutic levels at the site of infection and achieves a rapid response. This gives you the best chance to minimize lung damage.
Establish a consistent and systematic method for clinical assessment of calves before treatment and subsequent evaluation of results. A good option is the Calf Health Scoring System developed by Dr. Sheila McGuirk of the University of Wisconsin College of Veterinary Medicine. It can be viewed at www.vetmed.wisc.edu, downloaded or obtained from Bayer Animal Health in a Breathe Easy® BRD Detection and Treatment Kit. Contact your Bayer Food Animal Sales Representative or call Bayer Animal Health at 800-633-3796 to obtain a copy to use in your operation.
With a good plan in place and a systematic method for clinical assessments and evaluation of treatment results, you can minimize the damaging effects of BRD in your replacement heifer calves and help protect their future productivity.
Contact Dr. Sears at firstname.lastname@example.org.