Many Texas Longhorn breeders are uncertain about Johnes Disease and how it affects cattle.
Currently there is a big push in the Texas Longhorn industry to test cattle which are consigned to sales for Johnes (pronounced Yo-nees) disease. Many Texas Longhorn breeders are uncertain about this disease and how it effects cattle, about testing, what is involved, how reliable the tests are and if a false positive test can occur. I hope this article will help answer some of those questions and make breeders more comfortable with testing their cattle and dealing with issues if some cattle are found positive.
This is a Texas Longhorn cow showing advanced stages of Johnes disease.
Johnes disease is a chronic enteritis of ruminants caused by M. paratuberculosis. When the disease was first recognized in cattle as early as 1905 it was thought to be tuberculosis in cattle but was proven to be caused by a different organism and was originally referred to as “pseudotuberculous enteritis”; a designation meaning inflammation of the intestine resembling intestinal TB but not actually the same as intestinal TB.
Dr. Heinrich A. Johne was a pathologist and Professor of Pathology at the veterinary school in Dresden, Germany and one of the early researchers of the disease. The disease was brought to the United States by dairy cattle imported from Europe. It was first recognized in the US in dairy concentrated Pennsylvania in the early 1900’s and has unfortunately spread into all breeds of cattle since then.
The disease is now known as Mycobacterium paratuberculosis, which, by microbiology convention, is simply written as M. paratuberculosis (MAP). The organism that causes M. paratuberculosis can be spread from an infected cow through her feces, her milk to her newborn calf and even through her blood in utero to her calf before it is born. One major difficulty in defeating the disease is that a cow can be infected with the organism and not show clinical signs for 2-12 years, thus silently spreading the disease to offspring and her herd mates. So, it is commendable to help prevent the introduction of infected cattle into uninfected herds in our industry. As a matter of fact it would be advisable for all breeders to determine the status of their herd through testing and prevent the introduction of infected cattle by insisting that purchased cattle also be tested or at a minimum be quarantined until testing can be completed.
This is a dairy cow showing a condition known as bottle jaw associated with low blood protein commonly seen with Johnes disease.
Ruminants are a natural host for M. paratuberculosis. A natural host is one that does not mount an immune response that ejects the microbe from the body and the microbe does not kill the host – at least not for a long time. MAP causes a thickening of the lining of the small intestines. There is a chronic inflammatory response to the presence of the organism and this thickening prevents the absorption of nutrients for the animal. Other than being thin and having chronic diarrhea, a cow may not appear sick. She typically eats well, does not run fever but just progressively goes downhill. The signs can be subtle early in the disease and therefore not recognized. Owners may try deworming the animal multiple times with no success. So, an infected cow may stay in the herd for years. Some unscrupulous breeders will consign such an animal to a sale where an unsuspecting buyer may purchase an animal at a “discounted” price thinking the animal just needs better feeding and conditioning.
Example of an extremely thin beef cow that is in advanced stage of Johnes disease.
Sale hosts are more commonly requiring or strongly suggesting animals consigned to a sale be tested for Johnes disease prior to the sale. While this is very commendable and can help prevent the spread of the disease, consignors need to be aware of certain things about testing. The testing for Johnes must be done well in advance of the sale so that any positives or false positives can be detected, and appropriate measures taken to substitute a test negative cow in the sale.
Testing for Johnes disease
There are basically two types tests for Johnes disease: one focuses on finding the organism (MAP) in the feces of the animal and the other looks for antibodies to the organism in the blood of the animal. First, it is bests to test an entire herd to determine the prevalence of Johnes in the herd rather than testing an individual animal. This can be expensive and time consuming and therefore many breeders are reluctant to do it, especially if they have not seen animals in their herd with symptoms. Even if all animals are tested, an owner still cannot call the herd “Johnes free” because of the long incubation period of the disease.
There are specific requirements set up by states to follow over years of testing and culling for a herd to be officially called “Johnes free.” So, some breeders question the testing of an individual animal and the value added by that testing. But it is a place to start and as more breeders want to know the status of animals they purchase to bring into their herds, it is a very reasonable request.
This is an example of the severe diarrhea a cow can have with Johnes and how the stool can look from an animal with Johnes. This is why an animal is unable to absorb nutrients from the food it eats.
The serum ELISA is the most common screening tests done. This test is for the detection of antibody against Mycobacterium avium subspecies paratuberculosis in the serum. While the average specificity of ELISA Johnes test is 97-99% a rare false positive can occur from a cross reaction to another environmental mycobacteria. There can also be a subset of animals that test negative with the ELISA test but are still shedding MAP.
There are other tests that look for the organism directly in the feces of cattle; the Johne’s direct fecal PCR, Johne’s culture or pooled fecal culture. These tests yield more definitive information, but they are also quite a bit more expensive.
Regardless of which test is chosen it should be done early enough to make decisions based on the tests results well in advance of the sale to which the animal is consigned.
While Johnes is commonly associated with middle-aged to older cattle, even very young calves can be affected with the disease.
Johnes disease is not an easy disease to eliminate from a herd but the consequences of managing a herd with Johnes disease is very expensive and quite challenging. So, it is much better to know the status of one’s herd and be sure not to introduce Johnes infected animals into the herd.
For those breeders interested in knowing more about this disease:
the following link is very information and quite all-encompassing: https://johnes.org/johnes-disease-a-to-z/