Johne’s Disease-causing bacteria are around the farm
Environmental sampling on infected farms farms shows that the bacteria that causes Johne’s Disease can be found commonly, and, therefore, represents a threat to vulnerable animals.
Johne’s Disease (JD) is a disease of the small intestine caused by the bacterium Mycobacterium avium paratuberculosis (MAP). As the disease progresses in infected cows they shed the bacteria in their manure—100 to 140 pounds of manure every day. At first, bacterial shedding may be intermittent, but eventually, it will become continuous with as much as 1,000,000 bacteria per gram of feces. Therefore, the potential exists for widespread dissemination of the bacteria in the environment through the manure of an infected cow.
Samples were taken throughout the farm including the floor, feed and water of housing areas for calves, heifers, lactating cows and the maternity pen as well as samples from the manure pit, spreader or recycled sand pile. Of the 731 samples taken, 81 (11%) tested positive for MAP.
The most likely samples to be culture positive (46%) were samples from the manure storage or spreader. We can easily understand that when all manure is pushed into a pit or loaded into a spreader that the impact of shedding by individual animals can be detected.
The MAP pathogen was also cultured from 39% of samples taken from the floor of the lactating cow barns. It would follow that as employees or other personnel are in the cow pens, they pick up manure on their boots and clothes. This may serve as a source of JD transmission to other parts of the farm (or even to other farms). Of most importance would be transmission to areas where youngstock are housed as these animals are most susceptible to JD infection.
Detecting the bacteria in environmental samples was related to the prevalence of the disease in the herd. When the JD prevalence was found to be greater than 2%, MAP was cultured from the lactating cow floor or manure storage 75% of the time. In addition, positive samples were obtained from floors of each age group sampled including calves (9%) and heifers (5%). Even more critically, MAP was commonly found in the maternity pen. The maternity pen results will be discussed in a separate article.
There are several implications of this distribution of MAP bacteria on infected farms. First, environmental sampling is an easy way to tell whether a herd is infected. Taking a sample from the manure pit or other common cow areas (e.g. the scrape alley or holding pen) can tell us if there are positive and shedding animals in the herd. However, it would be best to base any negative conclusion on multiple samples taken over time since even in infected herds, negative environmental samples do occur.
The second major implication is that the MAP bacteria can be widespread in the environment on infected farms. Implementing practices to reduce the spread on farms of manure and the pathogens it carries is biosecurity. Most critically, management practices should be implemented that reduce the risk of adult cow manure being carried to young animals on clothes and boots, shared manure/feed handling equipment, runoff, waste feed from adult cows to heifers, and fence line contact. Truly, in this case, cleanliness means protection.
Learn more about the Michigan Johne’s Disease Control Project.