Johne’s Disease: What have we learned from our Demonstration Herd Project? (Part 1)

William Shulaw DVM, Beef and Sheep Extension Veterinarian, Ohio State University

In late 2003, the USDA provided funding for interested states to participate in the National Johne’s Disease Demonstration Herd Project. The primary objective of the project is to evaluate the long-term effectiveness and feasibility of various management-related disease-control measures for Johne’s disease on dairy and beef cattle operations. Secondarily, the program has provided for educational opportunities for producers and veterinarians highlighting diagnostic testing and management and control strategies. Currently, 17 states with 66 dairy herds and 22 beef herds participate in the program. Ohio enrolled three herds in the summer of 2004, one dairy herd and two beef herds.

In Ohio, the beef cattle herds have been tested by individual animal fecal (manure) culture and blood serum ELISA testing every spring and fall since the fall of 2004. In addition to the individual animal tests, samples of the farm environment have been taken for culture of the causative bacteria; udder skin surfaces have been sampled for culture; and individual animal fecal samples have been pooled in groups of five for culture. Several other “spin off” projects have also been conducted. A large amount of data has accumulated as well as a number of observations concerning management of the disease. So after four years of intensive testing in Ohio, what are some of the things we learned?

Cows shedding Mycobacterium avium subspecies paratuberculosis (MAP – the cause of Johne’s disease) in their manure contaminate the environment with these bacteria which are then ingested by susceptible calves. After an incubation period of several months to several years, these animals may show the classic signs of weight loss and diarrhea and pass large numbers of MAP in their manure. However, most animals shed MAP for months to years before they show any signs of disease. We have known these things for a very long time. Nevertheless, we have only recently begun to appreciate just how many of these bacteria are actually being shed by some cows and how severely the environment can become contaminated. The environmental samples and udder and teat skin samples we have collected show just how severe this can be.

The udder and teat skin samples were collected by rubbing a small section of the skin of the udder at the base and side of the teat for fifteen seconds using a sterile gauze sponge soaked in sterile water. Care was taken to avoid any fresh manure on the skin. The gauze was taken to the lab where any barn dirt was mechanically shaken off, the gauze removed, and the dirt processed for culture much like a fecal sample taken from a cow’s rectum. Results from one of the beef herds may serve to illustrate the potential exposure an udder could provide for a calf. During the spring of the first year of the Project, we collected udder scrub samples and fecal samples from all cows in the herd. The herd had calved in a dry lot setting prior to going to pastures, and nearly all the calves had been born and were nursing their mothers at the time samples were collected. Of 88 individual animal fecal samples, 7 cows were culture positive, but of the 88 individual udder and teat skin samples, 33 were positive. Furthermore, a few of these skin samples had numbers of MAP in them approximately equal to that of manure samples taken from the rectums of cows that are classed as “heavy” shedders! Remember that these skin samples were taken only one time in a small area around one teat. Imagine the potential exposure a calf nursing that udder several times a day could get. At another sampling session the following year, only two of 117 animals were fecal culture positive, but 4 of 113 udder skin samples were positive, and all of these were on fecal culture-negative cows. Cows shedding MAP into the environment can make the udder of many of their herdmates sources of infection for the calves.

Results from the samples we collected from the environment on these farms were also revealing. At each visit we collected twenty samples, equivalent to about two ounces, of dirt, bedding, or manure slurry from various areas such as free stall alleyways, calving areas, and dry cow pens at the dairy farm, and loafing areas, around round bale feeders, and the calving areas at the beef farms. We strived to get bedding material or dirt from the pens that would mirror what a calf would get exposed to in the pens and lots or on its mother’s legs and belly. In general, when the numbers of infected individual cows were very low, the numbers of environmental samples that were positive was also low. However, the presence of many infected cows, or a few so-called “heavy” shedder cows, made it easy to find MAP around round bale feeders, in loafing areas, and in the calving area.

For example on one recent sampling on one of the beef farms, again when all the calves were born and nursing their mothers, a two-year-old heifer was found to be a heavy shedder. There were an additional 7 of 145 animals that were also culture-positive but which were classed as moderate to light shedders. Two of five samples taken from around round bale feeders, and two of five samples taken from a two-acre drylot/loafing area were positive. Because the calving area had been divided into two separate areas for calving and housing the calves and their mothers, and because one of the loafing areas could not be sampled, the remaining ten environmental samples were taken from these two areas. All ten of these samples were culture positive and all ten would have been classed as a “heavy shedder” if they had been taken from an animal! Because the culture-positive two-year-old had access to both these areas, we believe she was responsible for much of the heavy contamination of the entire area. Udder and teat skin samples were not collected from cows at this sampling, but I have no doubt that a high percentage of them taken from cows in this environment would have been culture-positive thus creating great risk of infection for this year’s calf crop. Of course the calves were housed in this area too and had exposure to the same environment.

Next week in Part 2 we’ll take a look at Johnes testing alternatives.