buffalo field campaign yellowstone bison slaughter Buffalo Field Campaign
West Yellowstone, Montana
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Yellowstone Bison Slaughter
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Brucellosis in Wild Bison Fact Sheet
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Summary: Brucellosis was first detected in the Yellowstone Buffalo herd in 1917. The buffalo were exposed to brucellosis by domestic cattle that were grazed in the park and held in confinement with buffalo. Brucellosis is most commonly transmitted among and between species through ingestion of infected birthing materials. Yellowstone buffalo developed a natural immune response to brucellosis and do not typically suffer from the disease. It is believed that many buffalo may also have a genetic immunity to brucellosis. Failed pregnancies, the most common symptom of brucellosis, are relatively unknown in Yellowstone buffalo. The most likely mode of exposure among buffalo is ingestion of small amounts of bacteria from newborn live calves. Essentially, the buffalo in Yellowstone are vaccinating themselves for brucellosis, developing an immune response, and clearing the bacteria. There has never been a documented case of brucellosis transmission between buffalo and domestic cattle under natural conditions. In Grand Teton National Park, where vaccinated cattle and brucellosis exposed buffalo have been commingling for decades, no transmission has ever occurred. The chances of transmission between wild buffalo and vaccinated domestic cattle have been characterized as “very low”.

Issues: A number of factors including the incidence and transmitability of brucellosis in buffalo, the distribution of cattle in the Greater Yellowstone Area, and the regulatory structure in place for brucellosis relate to the current situation that has led to the death of nearly 4,000 buffalo since 1985.

1. Testing methods: There are currently two methods to test buffalo for brucellosis exposure and infection; serology and culture. Serologic testing involves drawing blood from live animals to determine if long-term antibodies for brucellosis are present. Buffalo that test positive are considered infected and sent to slaughter. Approximately 45 percent of Yellowstone buffalo test sero-positive on the CARD test, the one most commonly used by the agencies. Culture testing involves tissue sampling from slaughtered buffalo to determine if actual bacteria are present. Culture testing is considered to be the “gold standard” in determining infection. Drastic differences between sero-positive and culture positive buffalo indicate that many buffalo are being slaughtered simply because they have developed immunity to brucellosis and are not actually infected. A combination of test results indicate that only between 2 and 20 percent of buffalo actually have brucellosis bacteria in their bodies at any given time.

2. Transmitability: The most likely method of transmission between species is ingestion of infected birthing materials from an aborted fetus. Buffalo bulls, calves, yearlings and non-pregnant females do not pose a significant risk of shedding infected materials in the environment. When a female buffalo is infected with brucellosis, she will pass the bacteria in her first pregnancy. After the first calving, the uterus will “superprotect” itself from brucellosis preventing infected material from being shed in subsequent calving even if she is re-exposed. Therefore, only pregnant female buffalo in the first calving cycle after exposure have the possibility of shedding infected material in the environment. Brucellosis related abortions, even among infected females, are extremely rare in Yellowstone buffalo. Given the very small segment of the population that can even potentially transmit brucellosis combined with the low probability of transmission occurring in natural settings, the real chances of brucellosis transmission are extremely low. Additionally, brucellosis bacteria will not survive in warm weather and direct exposure to sunlight, and the activity of predators/scavengers all but guarantee that fetuses or infected birthing material will not persist in the environment beyond mid-May.

3. Distribution of Cattle: Relatively few cattle graze in the GYA at any time of the year, particularly in the winter and spring months when transmission is even a possibility. In the Western Boundary Area, no cattle are present within 45 miles of Yellowstone National Park in winter and spring. Cattle are typically only in the area between mid-June and mid-October, a period when there is no possibility of brucellosis transmission. The vast majority of cattle that graze in the summer in the Western Boundary Area are imported from Idaho and are already subjected to brucellosis vaccination and testing. In the Northern Boundary Area, there are never any cattle on the west side of the Yellowstone River between Gardiner and Yankee Jim Canyon. One producer grazes about 25 cows on the east side of the Yellowstone River approximately 4 miles north of Gardiner on Rt. 89. This same producer brings his cattle to private land adjacent to the Eagle Creek Special Management Area in the spring months. Untested buffalo are allowed to be in the Eagle Creek SMA as well and no transmission of brucellosis has ever occurred. One additional producer grazes cattle on the east side of Yellowstone River north of Gardiner. Both of these ranchers have publically stated that they welcome wild bison on their properties and are not concerned about a brucellosis transmission.

4. Regulatory issues: Montana is currently certified brucellosis class free. Class free status allows producers to transport reproductive cattle across state lines without brucellosis testing. The United States is not certified brucellosis free by the OIE, the international regulatory body. Therefore, brucellosis testing is required to transport reproductive cattle across international boundaries. In order for the US to be certified brucellosis free by the OIE, no livestock in the country can have been vaccinated for three years.

Conclusion: Only a relatively small percentage of Yellowstone buffalo are actually infected with brucellosis. Brucellosis does not have any significant impact on the health of the Yellowstone buffalo. The risk of transmission from wild buffalo to cattle is infinitesimally low. Relatively few susceptible cattle graze in the GYA and most are not present when transmission is even a possibility. Herd management plans that adjust stocking dates could be developed to insure that transmission does not occur. Montana can easily comply with the National Brucellosis Eradication Program to insure that brucellosis class free status is preserved. The GYA could be exempted from the OIE certification process and allow the rest of the country to enjoy international brucellosis free status. Montana can develop risk management strategies for domestic cattle to allow for wild, free roaming population of buffalo in GYA and beyond.

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