TUBERCULOSIS: What Does Discovery Of Bovine Tuberculosis In A Herd In Ohio Mean For Ohio Livestock Farmers?

09/01/2010
The July 7, 2010, press release from the Ohio Department of Agriculture announcing that a dairy herd had recently been detected with bovine tuberculosis (bTB) and subsequently depopulated was perhaps a surprise to some people, but to those who have been observing similar kinds of discoveries in other states, it was not. In fact in an article in the Ohio BEEF Cattle Letter that appeared just before the ODA press release, we briefly discussed biosecurity and the concern of introducing diseases, like tuberculosis and others characterized by "silent" infections, into herds and flocks. In the short term, the impact of this discovery on Ohio farmers will be rather minimal and limited to the herd affected, the herds in which animals from this herd were traced, and the regulatory agencies charged with the tracing and testing activity (of course they are supported with our tax dollars). Should additional herds be discovered in the next two years, the possibility of loss of our "free" status with respect to bTB exists. This could have a profound impact on Ohio farmers.The current situation in Ohio and the USA, with respect to bTB, does give us some insight into changes that have occurred over the past 20-30 years. Herd size has tended to increase, especially in the dairy industry. Some of this expansion occurred with retention of natural additions to herds, but for many herds it also involved movement of animals from one herd to another. In some cases bTB has been traced to Mexican cattle entering the US as Holstein feeder animals and roping/rodeo steers. Unfortunately, in a few cases contact between these animals and other animals destined for breeding herds has occurred. This time frame has also seen the growth of farmed deer, elk, and bison herds, much of which was unregulated until recent years and in which some level of bTB may have persisted.The conspicuous feature of this change is the nature and amount of animal movement. In a recent news article, it was reported that last year more than 19 million of the nation's 30 million beef cows and 9 million dairy cows crossed state lines. (1) It is now fairly common for herds, both beef and dairy, to contain animals that were born in one state; raised, comingled with other animals, and bred in one or more different states; and relocated to yet another for breeding or production purposes. In fact, in the Ohio herd recently found with bTB, the animals in that herd had their origin in at least 17 different states and Canada. Much of this movement is done with no, or minimal, attention to the potential for introduction of disease. Some of it is done illegally; perhaps more than we would like to believe. The recent National Animal Health Monitoring System surveys suggest that routine biosecurity measures for animal disease prevention are not regularly practiced by many farms. (2) Diseases like bTB, Johne's disease, anaplasmosis, and BVD are readily moved about by animals that are infected but which show no visible signs of disease. This tremendous amount of movement of animals back and forth across the country, which happens virtually every day, has led some people in the animal health field to observe that we now have a "national" herd merely split up among different temporary owners. To the extent that animals are moved without individual identification and records, the job of tracing disease outbreaks becomes enormous. Perhaps this is a good time to discuss "health certificates." Actually, the term "health certificates" is a bit of a misnomer since they do not really certify the complete "health" of the animals being moved. Although the term is still used almost universally, today it is reserved for forms and certificates provided by the USDA for interstate and international animal movement (including dogs and cats). Most states, including Ohio, now issue a "certificate of veterinary inspection" which perhaps more appropriately describes what they are. They are the paperwork that is usually required for interstate, and sometimes intrastate, movement of animals. They list all official forms of identification of each of the animals, their source/owner and destination, and the results of any tests that may have been required for movement to the destination. In some cases, no actual animal tests are required. They also require the signature of a veterinarian that indicates that he/she has performed the appropriate tests, that the information on the certificate is correct and complete, and that he/she has examined the animals for evidence of infectious or contagious disease. Some states require additional statements regarding the status of a specific disease for the source herd to be placed on the certificate. An accredited veterinarian and state of origin issue the certificate with the original accompanying the animal and copies sent to the state of destination.Although the certificate of veterinary inspection is a very important legal document and does verify testing and examination for some kinds of diseases, it does not imply that the animals listed on the certificate are free of disease. For infectious diseases that have long incubation periods, like bTB, or diseases that may be transmitted from apparently healthy carriers or shedders, like Johne's disease, BVD, or anaplasmosis, a "health certificate" may provide little protection to the farm or herd of destination. Furthermore, the requirements for interstate and intrastate movement may vary somewhat by state depending on what a state believes is in the best interest of their citizens. For example, a disease of beef cattle that is getting more attention every year is trichomoniasis (commonly called "trich"), an infection carried by non-virgin bulls that can be transmitted to cows at breeding and cause early embryo loss and a high level of open cows at calving. It has been most common in several western states and is gradually spreading other states. Some states require multiple tests for this infection on bulls prior to them entering their state, and some do not. Currently a farmer in Ohio can buy a potentially infected bull from another state and move it to Ohio without any testing for this disease.The United States embarked on a bTB eradication program in 1917 at a time when an estimated one in every nine human deaths was from tuberculosis. It has been estimated that 10% or more of those human tuberculosis cases were due to the bovine form acquired from cattle or indirectly from cattle products. (3) That estimate does not count the crippling, non-fatal infections. We made astounding progress in just the first few decades, thanks to the financial and moral commitments of your grandparents and mine, and we continued to make significant strides toward eradication through the early 1990s when most states were declared "Free" and granted that status by the federal government. [For a very interesting account of this read (3)] Today many states do not require tuberculosis testing for cattle being imported from "Free" states. In the next installment of this series, we will discuss the meaning of a bTB Free status today.
Source: William Shulaw, Extension Veterinarian, Ohio State University
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