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Newsletter of Penn Dutch Cow Care July 2004

Hi Folks,

           J is for July, but it can also stand for Johne’s, which is what I would like to discuss this month. Most producers are very aware of the obvious clinical signs of Johnes: a cow that keeps on eating yet won’t quit scouring no matter how much hay you stuff into her and she keeps getting skinnier. The final straw is when she develops “bottle jaw” – the soft fluid build-up under the jaw that slowly becomes larger. If you have ever had one of these cows, there is a very high likelihood that you have more cows infected but not yet showing clinical signs. But they are still likely shedding it into the environment.           

So what causes Johnes disease and when does it begin? The disease itself is a syndrome (as just described), which initially gets its start when the Mycobacterium avium paratuberculosis (MAP) colonizes the gut. There are likely nutritional and genetic factors which affect the animal’s ability to withstand infection, as there are for any infection. However, it is extremely well documented that the environment in which the animals live plays a major role in the spread of infection to new animals. Calves are definitely the most susceptible, especially at the time of birth. Calves made to be in areas where there is adult cow manure (especially from cows shedding the actual organism in the manure) will most likely to pick up the disease either by sucking on dirty, manure coated teats or by nibbling the bedding around them that has adult manure on it. The most susceptible are new born calves within the first 72 hours of life. This is because the calf’s gut which is “open” to absorb the beneficial colostrum of its mother unfortunately can also absorb viruses, bacteria and toxins. As the calf’s immune system matures and the animal can mount a defense against outside invaders into its system, the likelihood of MAP inoculating the gut lessens. Adult cows are fairly resistant to it unless experimentally inoculated with it by tube feeding the MAP organisms in high concentration.

 The MAP organisms that do inoculate the gut cause a reaction in the animal which tries to fight it off as best as it can. The reaction between the bacteria and the animal’s immune system thickens the wall of the gut very slowly (specifically the small intestine) and eventually thickens it so much that the ability of the intestine to absorb fluids is decreased and diarrhea starts to occur. Diarrhea is simply a condition in which the intestines and colon do not re-absorb fluid as they normally should and the result is very fluid manure (scours). The diarrhea is usually an effortless, pipe-stream diarrhea. The cow doesn’t strain as it puts out large quantities of manure. As the cow scours on and on, she is also losing protein from her circulatory system. The decreased protein levels make for leaky vessels and this is when the bottle jaw occurs.

 There are various tests that can be run to detect MAP infection in a cow. In order of increasing sensitivity, the test which only picks up very clinical cases is the AGID test. This test only takes 3 days to run. The next best test is the ELISA test which detects if antibodies are being generated by the cow to MAP. It is about 80% accurate if screening a whole herd. It is nearly 100% accurate if testing an individual cow with clinical symptoms. Milk can now also be sampled for presence of antibodies to MAP during your monthly DHIA sampling. The blood testing and milk testing are considered to give equivalent results and will end up costing roughly the same amount. The “gold standard” at picking up the slightest level of infection is the fecal culture which unfortunately takes 12-16 weeks until there is an answer.

 Although testing and culling will reduce the amount of animals shedding the MAP into the farm surroundings, some herds will still be vexed by Johne’s even with near perfect management. It is at that time that vaccinating calves between 1-35 days of age could be considered. In Pennsylvania, we are allowed to vaccinate calves against MAP as long as the farmer commits (by signing up) to a program to maintain management so that infection will not spread (by using separate feeding implements and manure implements for adult cows and for calves). Blood or milk ELISA testing can no longer be done since it checks for antibodies, which of course will be present due to vaccination. The other thing is that animals will usually have a lump on the brisket at the site of vaccination that grows along with the animal. The bright side is that a farmer doesn’t need to vaccinate forever, only for a few years until the worst cows are gone and management practices are firmly in place.

 A voluntary, national testing and management program is soon to be launched. It is based partly on the Handbook for Veterinarians and Dairy Producers which is a guide for Johne’s disease risk assessments and management plans to improve biosecurity and reduce pathogens. The handbook is broken out into calving area, pre-weaned calf group, post-weaned calf group, bred heifer group and cow group. Some questions for the calving area are: Is the area used for more than one calving cow at a time? Does manure build-up in the calving area pose a risk for calf ingestion? Are sick cows kept in the calving area? Are high risk/ Johnes clinical and suspects in calving area? Are calving cow’s udders soiled with manure? Are calves born in other areas that hold cows i.e. outside the calving area? Do calves stay with their dams for >60 minutes? Are calves allowed to nurse dams?    I realize that there are many farmers who allow a calf to nurse its cow. And there are other farmers who intentionally have nurse cows for many calves. While I agree with these practices, it would be wise to test any cows for Johne’s that are allowed to nurse calves. The MAP organism can be cultured from raw milk and would make for an easy route of infection. There are no questions regarding length of time calves are on cows in the section on beef operations, however, there are still questions regarding beef calf access to clean water and clean surroundings. Questions for risk assessment in the pre-weaned group include: Is colostrum pooled from multiple cows and fed to calves? Is colostrum fed from individual cows to calves? Is unpasteurized milk pooled and fed to calves? Can calf’s colostrum and/or milk be contaminated at any time? Can calf’s feed or water be contaminated with manure at any time? Are calves able to come in contact with cows or cow manure in the environment? Questions for risk assessment in the post-weaned group (until a year of age) are: Do heifers have contact with cows or their manure? Is it possible for manure from cows to contaminate feed? Is it possible for manure from cows to contaminate water sources? Do heifers share pasture with mature cattle? Is manure spread on pasture then used by or fed to heifers?

 Obviously, the less contact with adult manure, the better. Yet it can still be very difficult to do all the management practices to keep calves from cow manure. Change can be very difficult when you are used to a routine. But at least by testing your herd, you know where you stand in regards to this disease and can then make appropriate changes if need be.


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