The potential link between Johne’s disease in cattle and human Crohn’s disease has made Johne’s disease a research priority for the beef industry. Johne’s disease is caused by a bacterium called Mycobacterium avium paratuberculosis (MAP). It is believed that cattle are most prone to MAP infection early in life, probably through the consumption of contaminated manure or colostrum. MAP then hides away and multiplies in the intestinal lining for a number of years. This eventually damages the intestinal lining and impairs nutrient absorption, resulting in the loss of body weight and condition, chronic diarrhea (which can infect more calves) and death.
The Beef Cattle Research Council and Alberta Beef Producers have supported several research projects that studied factors associated with Johne’s disease in beef operations. In the first three studies, cattle from 335 beef herds were tested for Johne’s disease across seven provinces, and a wide range of production and management information was collected. Statistical analyses were then used to examine whether 48 different environmental and management practices were associated with the risk that a herd would be infected with Johne’s disease. These projects were led by Dr. H. Morgan Scott (formerly with Alberta Agriculture, now with Kansas State University), Dr. Christine Powers of the Canadian Food Inspection Agency, and Dr. Steve Hendrick of the Western College of Veterinary Medicine in Saskatoon. A fourth study led by Dr. John Campbell of the WCVM provided some additional insights into the potential role of wildlife. Several particularly important risk and management factors were identified in these studies.
Colostrum is very important, but the source is critical. Calves are born before their immune systems are fully developed, so a newborn calf relies on maternal antibodies from colostrum for disease protection early in life. However, if the dam is infected with Johne’s disease, her colostrum can also be infected and pass the disease on to the calf. This means that when a Johne’s-suspect cow is culled, her daughters are probably infected and should be culled as well. Colostrum from Johne’s-suspect cows should not be saved for future use. Extreme caution should be exercised when sourcing “spare” colostrum from other producers. Pooled colostrum from a dairy should be avoided; the entire batch of colostrum will be infected if colostrum from one shedding cow is present. Colostrum should not be accepted from beef herds that appear to have Johne’s-infected cows. Finally, not all commercial colostrum replacers are equal. The Saskatoon Colostrum Company has developed a process that kills MAP while maintaining the antibodies. This product is more expensive than many alternatives, but is considerably less expensive than introducing Johne’s disease.
Ionophores may help. This is supported by other studies done in dairy cattle. Ionophores may reduce MAP shedding and reduce the risk that new animals will become infected. However, it does not appear to cure Johne’s disease in cows already infected.
Grazing management is important. In one study, continuous grazing was much more risky than rotational grazing. This may be related to the fact that cattle are less likely to pick up soil or manure when grazing pastures that are in better condition.
The role of wildlife is very unclear. In one study, herds that came in contact with deer were much more likely to test positive for Johne’s disease than herds where deer were never seen. Another study reported that operations with dogs (which could help keep wildlife off the yard, at least) were less likely to be infected with Johne’s. A third study indicated that beef herds in the Parkland and boreal forest regions of Alberta were more likely to have Johne’s than herds in grassland or mountainous regions. Some deer species prefer treed areas, but soil pH, alkalinity and moisture also differ among treed and open regions. These soil factors may also affect how long MAP can survive in the environment. None of these three studies actually collected any wildlife samples to culture for MAP. This is where the fourth study comes in. Dr. Campbell’s study collected 398 samples from a wide variety of wildlife, including a dozen fecal samples from deer, elk and pronghorn on six farms that were known to have Johne’s. No MAP was detected in any of the wildlife samples in this very small, preliminary study. This doesn’t mean that wildlife cannot harbor Johne’s disease, but it does suggest that they are not always the main culprit.
There is no quick fix for Johne’s. Preventing and reducing Johne’s disease requires a combination of management practices to avoid introducing infected cattle, colostrum or manure into the operation, and calving, feeding and grazing management practices that reduce the risk that young calves will consume infected manure and colostrum. These practices will contribute to overall herd health, particularly in terms of calfhood diseases like scours due to rota-and coronavirus,E. coli,Salmonella, Cryptosporidia, Giardia and Campylobacter.
It is believed that cattle are most prone to MAP infection early in life, probably through the consumption of contaminated manure or colostrum