A recent article in BEEF magazine created a bit of a stir among some veterinarians. In “Grappling With Mycoplasma,” (BEEF Feeder, May 2006), it's pointed out that mycoplasma as a disease of feeder calves seems to popping up in new areas with increasing virulence. Central to the story is whether or not the causative organism, Mycoplasma bovis, is a primary disease agent, or more of an opportunist, setting susceptible cattle up to infection from other viral and bacterial pathogens like the bovine viral diarrhea (BVD) virus.
The controversy though, surrounds Montana cattle feeder Dan Vogel's use of “high doses” of penicillin for treatment of mycoplasma. The concern is that since, as pointed out in the article by Ron Skinner, DVM, of Hall, MT, M. bovis has no cell wall, antibiotics such as penicillin and cephlosporins that work by affecting the cell wall are useless against mycoplasma.
Rolland Kramer, DVM, Logan County Veterinary Clinic, Stapleton, NE, in contacting BEEF, says he wants the record to be corrected. He says some antibiotics (other than penicillin and cephalosporin products) work against M. bovis because they affect other parts of the bacteria and that treatment with an inappropriate antibiotic (in this case penicillin) may make the disease worse.
Skinner and John Maas, University of California-Davis Extension veterinarian, feel Vogel, in using penicillin to treat for mycoplasma may be taking out some secondary organisms associated with the disease, as opposed to affecting the “primary organism” — M. bovis. Either way, while penicillin isn't effective against the organism, Vogel is seeing some kind of response to his treatment regime.
In an effort to shed other light on Kramer's concerns, we contacted Ricardo F. Rosenbusch, DVM, Department of Veterinary Microbiology and Preventive Medicine, Veterinary Medical Research Institute at Iowa State University.
“I can appreciate the interest of producers in finding means to lower the cost of dealing with mycoplasma problems,” he says. “But, there are risks being assumed.”
Those risks include:
Mycoplasma may not be the primary problem.
Stress levels on the cattle are unknown.
Wasting time with early ineffective treatments will escalate costs later.
“I struggle with a small body of hard evidence in answering the questions posed here,” Rosenbusch explains. “We've shown there is wide variation in pathogenicity among strains of M. bovis. This will impact directly on what the outbreak looks like.”
He says there are examples of mycoplasma outbreaks with 0% mortality and others where mortality reached 7% (much higher in small groups of cattle). Also, some outbreaks present signs of lameness (as in Vogel's case), though most don't.
Overall, it appears stress plays a critical role, Rosenbusch says. This can be body stress (due to shipment, weather, etc.) or joint stress (due to freezing ground, poor footing, etc). He also says other pathogens play a major role in making mycoplasma more severe. These pathogens are primarily Mannheimia haemolytica and BVD virus.
Treating M. bovis
So a producer facing an outbreak with an aggressive M. bovis strain, foot stress and persistent infection (PI) with the BVD virus in the feedlot, may not be able to control the disease with a penicillin product or related cell-wall antibiotics.
“We can cite multiple examples of this type of presentation,” Rosenbusch says.
In contrast, he says if the producer faces an outbreak where there is low stress, even with an aggressive strain of M. bovis, treating with penicillin may give results that are statistically as good as those obtained in treating with an antibiotic known to stop the M. bovis strain in question.
“We have a few well-studied examples of this,” he says. “We theorize that the M. haemolytica was controlled and this affected the mortality parameter, but it didn't reduce the percent repulls.” Therefore, he says there was moderate economic benefit to treating with the cheaper drug.
Bottom line, Rosenbusch says it's risky to depend on penicillin treatments to resolve a mycoplasma problem.
“But a producer may squeak by a few times,” he concludes. “We badly need controlled field studies on these questions of treatment, and prophylaxis in dealing with mycoplasma problems.”