Even if you maintain a closed herd, every dairy farmer should be concerned about Mycoplasma bovis because of the devastating economic and health impact it can have on a farm. It is true that maintaining a strictly closed herd is the single most important strategy that a farmer can employ to reduce the likelihood of introducing Mycoplasma into a naïve herd. However, there are many reported cases of closed herds having M. bovis outbreaks, and that has been our clinic’s experience as well.
M. bovis fits all the disease criteria to make it a perfect nightmare for dairy farmers. The bacteria is highly contagious, can survive in the environment for long periods of time and can spread between animals through milking machines, equipment used to treat animals, the milker’s hands, milk fed to calves, and by direct contact between animals. Cows carrying the bacteria may not show any symptoms and spread the infection to other cows. Additionally, infected cows may be difficult to detect as they only shed the bacteria intermittently. If we test on the wrong day or collect the wrong sample, an infected animal may have a negative test. Therefore, we cannot simply perform a single test of the entire herd to identify and remove the infected cows. There are no effective treatments for M. bovis in lactating cows, and no vaccines that have been shown to be effective in preventing infection. Infected animals often eventually succumb to the infection either due to death, culling or incurable disease (lameness, pneumonia, or mastitis). Following the initial outbreak (where 20-30% of the herd can easily be lost), asymptomatic carrier animals may intermittently develop disease during periods of stress such as calving, changes in nutrition, or bad weather and continue to transmit the bacteria to healthy herd-mates. Besides the economic losses, the mental stress of an outbreak of M. bovis on producers can be devastating.
Cases of in-curable mastitis, swollen joints, chronic pneumonias and calves with droopy ears or head tilts could indicate the presence of M. bovis on a farm. M. bovis is not often part of routine disease surveillance and must be specifically tested for. We suspect there are many herds in Western Canada (including closed herds) that have mycoplasma-infected animals which have gone undetected and contribute to the background of non-specific disease on farms. There has not been much attention paid to the prevalence of mycoplasma herds in Western Canada, and that may be eye-opening research to perform.
In an effort to prevent infections, producers that can’t maintain a closed herd should try to reduce exposure. Testing new animals during quarantine, cleaning equipment (calcium bolus guns, drenching tubes) between uses, improving milking hygiene, and discussing biosecurity disinfection expectations with farm service providers may be helpful approaches. Routine surveillance testing of bulk tank or waste milk is helpful for identifying herd level infections. Although Canada has not taken any serious measures to eradicate M. bovis, unlike New Zealand, the grave health and economic impact it has should concern all producers (whether or not you have a closed herd) and the dairy industry as a whole.
– Dr. Derk Pierik, Barr-North Veterinary Services