Dr. William P. Shulaw, Extension Veterinarian, The Ohio State University
Producers in Ohio have enjoyed a very high level of support for Johne's disease testing for many years. Although warning signs that this could change have been visible for the past two to three years, the changes that came about in March of this year were a surprise to some producers and veterinarians. What changed?
Actually, not all that much. Ohio still has a Johne's program that mirrors the federal guidelines of the Voluntary Bovine Johne's Control Program. Veterinarians still administer risk assessments and help producers develop management plans, much as they have in recent years, and Ohio still has one of the best-equipped and best-staffed diagnostic laboratories for Johne's disease in the USA. And Johne's disease is still costing the Ohio cattle industry enormous amounts of money in lost milk production and premature culling of animals. The only real difference, admittedly a very important one, is that the Ohio Department of Agriculture has been required to begin charging substantial fees for fecal cultures and ELISA blood tests. And the timing couldn't have been much worse. Why?
For the past several years, the same issues that have affected the budgets of other state agencies have steadily eroded the state-supported budgets for our veterinary diagnostic laboratory and Animal Industry Division personnel. At the same time, costs for materials and supplies to perform diagnostic tests have steadily risen. In addition, other diseases, such as avian influenza, chronic wasting disease, and viral hemorrhagic septicemia in Great Lakes fish have absorbed increasing amounts of dollars and personnel time. Johne's disease control and assistance to farmers has been a high priority for this State, and until recently, federal contract monies have offset much of the cost of testing and allowed Ohio to keep testing for Johne's disease free. This was possible because of Ohio's nationally recognized leadership in Johne's disease control efforts and the volume of diagnostic testing conducted in Ohio.
At the federal level, from a Congressional support level of about $18 million in 2002 for assistance in controlling Johne's disease, monies available to the states have fallen dramatically. Ohio's share of federal support monies has fallen from $910,000 to just over $200,000 this year which is being used to maintain the Test Negative Status Herd Program. The timing of this reduction is unfortunate in that many producers in Ohio have just begun to realize the seriousness of this disease in their herds, at least in large part because of the efforts of practicing veterinarians in helping them to assess their risks and to develop a sound management strategy. The good news in all this is that Ohio still received proportionally more money this year than most other states, but the bad news is that combined with weak state support, this amount is no longer sufficient to maintain all the free testing we have enjoyed in the past. Currently, culture for the causative organism of Johne's disease, Mycobacterium avium subspecies paratuberculosis or MAP, costs $25.50 per sample and ELISA on blood samples is $4.50 per sample. Because these are real testing costs, excluding labor, producers can get some idea of ODA's historical commitment to Johne's disease control.
Lack of State and federal dollars does not change the need to manage Johne's disease effectively to prevent continued financial losses and spread of the disease. If your only approach to Johne's disease control was a "test and cull-the-positives" approach, you may not have seen much apparent improvement in your situation, especially in the past couple of years when culture methods in use at the laboratory became more sensitive in finding infected animals. Culling infected animals, especially heavy shedders, can be very helpful in reducing the overall burden of MAP on the farm. But, if adequate steps aren't taken to effectively prevent transmission to calves and heifers, progress will be likely be very slow or absent.
Environmental sampling in this State, and others, has shown that even when the prevalence of infected animals in the herd drops below 10%, it is not difficult to find MAP in the cow environment and on the udder. These recent findings underscore the importance of developing a management plan that reduces the potential for a young calf to ingest MAP. In one of the herds enrolled in our Johne's Demonstration Herd Project, this was done by prompt removal of the calf and allowing someone else to raise the heifers at a completely different, but clean, site. In another of these Demonstration Herds, a beef herd, the producer made the decision not keep his own replacement heifers at all until he could get the prevalence of MAP-infected cows in his herd to zero. This necessitated buying a few heifers from herds in the Test Negative Program to maintain herd numbers, but because beef herds don't usually have the luxury of removing calves right after birth, this may be the most important element of his control program. This herd has gone from a 10% infection level in 2003 to zero for the past two years.
The maternity area is the place most calves are likely to get their first exposure to MAP. The sooner they can be removed to a clean place, the less the risk of them ingesting it and becoming infected. Likewise, the greater the environmental burden of MAP in the maternity area, the more likely the calf is to get an infectious dose before it is removed from the cow. Some veterinarians are now using environmental sampling of the maternity area as a kind of "report card" for overall hygiene and the risk to the calf. These samples of bedding can be taken at periodic intervals, perhaps quarterly, to assess overall contamination and the need to improve hygiene of that area. Research has shown that the udder, belly, feet, and legs of cows can be heavily contaminated with MAP and that the dry cow area may be a source of contamination for the maternity area, even if a cow about to calve is placed in a freshly cleaned and bedded calving stall. The dry cow area can also be sampled to assess this risk. Work we have done so far suggests that five samples for culture can give a producer and the practitioner a glimpse of the level of contamination of maternity or dry cow areas and the need for corrective action.
Quite a few states, including Ohio, have investigated the possibility of using pooled fecal samples for culture to: 1) determine whether MAP is present on the farm, and 2) estimate the prevalence of MAP infection in the herd. Although culturing pooled fecal samples from five cows at a time can reliably determine if MAP is in the herd, sampling the environment is less costly and probably just as efficient for that purpose in dairy herds. In fact, environmental samples can now be used by dairy herds for entry into our Test Negative Status Program at level one.
Pooling of fecal samples will not likely be useful to producers who already know they have a serious problem with Johne's disease; however, this approach can be useful to assess strings of cows in large dairy herds, and it can be useful in estimating the overall prevalence of infection in some herds that do not already have an idea of the prevalence or which have just found out they have an infected cow. Currently, samples can be collected by producers and sent to the laboratory, through their herd veterinarian, for pooling and culture. This may be attractive for owners of small beef herds where the cows are not handled frequently. Pooled sample results can be used to determine which groups of five animals may have "heavy" MAP shedders. Further testing can identify these animals for culling or segregation. Pooling could also be used to assess infection in groups of purchased animals. Pooling in groups of five substantially reduces the cost of testing and can provide valuable information to the herd owner.
We are currently assessing the usefulness of culturing heifers to see if it is possible to identify MAP-infected animals at a younger age and redirect them to options other than the milking herd. In addition, Ohio and other states are currently evaluating some additional approaches to individual animal tests that may be more sensitive than ELISA and less costly than culture. However, in the short term, producers can still use testing strategies that will help them manage this disease. They don't have to be costly. Consult with your veterinarian for options that may be useful in your herd.