A survey of records of bovine respiratory disease (BRD) cases at the Kansas State Veterinary Diagnostic Laboratory showed that drug resistance in Mannheimia hemolytica, one of the primary organisms associated with BRD, increased over the three year period from 2009 to 2011.  Researchers found that over that period a high percentage of the organisms recovered from cattle lungs were resistant to several of the drugs typically used to treat that pathogen.  Six antimicrobial drugs were tested.  Using the parameter of resistance to at least three of the six drugs as a definition of multi-drug resistance they found that 63% of the bacteria were multi-drug resistant in 2011 compared to 46% in 2010 and 42% in 2009.

Several factors are known to contribute to the development of drug resistant organisms.  These include use of antimicrobial drugs when they are not indicated, improper dosing, and failure to follow label directions.  Perhaps the greatest factor is discontinuance of the therapy when improvement is seen rather than maintaining drug levels throughout a full recommended course of treatment.   To prevent or delay the development of resistance, always follow closely the label as well as your veterinarian’s directions.

While many of the recovered organisms were resistant to three or more of the six antimicrobials tested, none were resistant to all six.   This emphasizes the importance of antimicrobial sensitivity testing that can be done easily and inexpensively by your veterinarian or the Oklahoma Animal Disease Diagnostic Laboratory.   Using the right drug for the particular organisms causing your BRD problems not only helps to prevent the development of further resistance but also minimizes death loss, economic loss, labor, and animal suffering in your herd.

Source: Dave Sparks DVM, Oklahoma State University Area Extension Veterinarian