USDA works on better tests for cattle TB

USDA works on better tests for cattle TB

*Krissa Welshans holds a bachelor's degree in animal science from Michigan State University and a master's degree in public policy from New England College. Welshans has long been involved in agriculture and has worked with numerous agricultural groups, including the Animal Agriculture Alliance.

IMPROVING tests and vaccination methods is one strategy U.S. Department of Agriculture scientists are using to overcome obstacles that prevent the eradication of bovine tuberculosis (TB) in cattle worldwide.

Scientists at the Agricultural Research Service (ARS) National Animal Disease Center in Ames, Iowa, are developing new methods to prevent and control TB in cattle and white-tailed deer.

Veterinary medical officers Ray Waters and Mitch Palmer and microbiologist Tyler Thacker are collaborating with international groups, other U.S. government agencies, the cattle industry and private companies to combat TB. They are developing better tests to help producers identify and remove TB-infected cattle from herds and keep healthy animals.

Widespread pasteurization of milk, development of a diagnostic tuberculin skin test for cattle and establishment of a USDA eradication program have significantly helped decrease the incidence of bovine TB in humans in the U.S.

While the tuberculin skin test for cattle has helped eradication efforts, it does have drawbacks.

"The test is not sensitive enough and requires a 72-hour waiting period for results," Palmer said. "It's very difficult to test a herd of 100 cows and say that this one has TB and this one doesn't because the test may not detect one or two animals that actually have TB."

Interferon-gamma-release assays, another method used to detect TB, are whole-blood tests that require live white blood cells to work. Fresh blood samples must not get too hot and must be processed within 8-30 hours, which requires getting samples to a lab in good condition within a reasonable time frame, Waters said.

He pointed out that tests requiring only the liquid part of the blood, the serum, would be more convenient and less expensive.

The problem is identifying antigens that are very specific and sensitive for use in serum tests, he said. An antigen is a substance — like foreign bacteria or viruses or matter within the body — that causes the immune system to produce antibodies against it.

Waters said over the last 12 years, scientists in the Ames lab have shown that improved antigens, such as one known as "MPB83," are crucial in developing effective assays. These findings played a key role in a new serum TB diagnostic test developed by IDEXX Laboratories Inc.

According to Waters, this test is more convenient and could potentially be used in combination with skin and interferon-gamma tests to identify undetected TB-infected animals. "It's another tool in our diagnostic toolkit," he said.

Waters pointed out that, until recently, the skin and interferon-gamma tests were the only approved tests for use on U.S. cattle. However, the U.S. recently approved serum tests for use with samples from deer and elephants. Even more recently, the IDEXX M. bovisELISA test was approved for use with samples from cattle.

Thacker has developed another type of test based on polymerase chain reaction (PCR) analysis of DNA. The new PCR test detects Mycobacterium bovis, the causative agent of bovine TB, in fresh tissues rather than the traditionally fixed tissues prepared for viewing under a microscope. It is quicker, accurate and helps distinguish between M. bovis and environmental mycobacteria that can cause false-positive results.

"The objective was to be able to confirm M. bovis in fresh tissue to speed up the process," Thacker said. "That way, we wouldn't have to wait potentially two months for the bacterium to grow."

Last, there is the Bacillus Calmette-Guerin (BCG) vaccine, which is safe and has been partially effective against TB in humans for more than 100 years. The BCG vaccine was first tested in cows and showed protection against virulent M. bovis. Soon afterwards, it was used in humans and demonstrated protection against Mycobacterium tuberculosis, the most common cause of TB in humans.

"Rather than trying to reinvent the wheel, BCG seemed like a logical choice to try with deer," Palmer said. "We're looking at its efficacy in deer. Does it actually protect them? Are there any undesirable side effects? Is it safe to use in deer that may become food for hunters?"

Today, several different strains of BCG are used to vaccinate people in countries where TB is still a problem. BCG is not used in the U.S., however, because those who have been vaccinated might test positive when given a TB skin test, even if they don't have the disease.

"The concern wasn't that BCG was going to hurt people; it doesn't produce disease or cause an infection. The concern was that if a person ate venison from deer vaccinated with BCG and subsequently had a skin test for TB, the result might be a false positive," Palmer explained.

Palmer and his colleagues fed a BCG oral bait vaccine to captive deer and examined them one to 12 months later to determine how long the vaccine remained in the deer.

BCG was not detected in deer given a standard dose. Deer that received elevated dosages — 10 times the standard — had traces of BCG in their lymph nodes and other tissues not commonly used for food. The vaccine was never found in common cuts of deer meat in any of the safety experiments.

Although the BCG bait, which resembles a hard cookie, worked well for captive deer in Iowa, it did not appeal to wild white-tailed deer in Michigan.

Palmer and his team are collaborating with scientists at USDA's National Wildlife Research Center in Ft. Collins, Colo., to develop a new bait to deliver the BCG vaccine to deer. They are experimenting with apple, acorn and peanut butter flavors in hopes that one of these will appeal to wild deer and provide an effective vaccination delivery method.


Bale feeder choice

Recent drought has meant that cattle producers cannot afford to waste a valuable resource like hay in even the best years.

"Management of input costs is a key business concern and can mean the difference between operational profit or loss, and when it comes to hay waste, using the right type of bale feeder can make a significant cost-savings difference," said Dave Lalman, Oklahoma State University Cooperative Extension beef cattle specialist.

Research conducted by Lalman and other scientists with the Oklahoma State University Division of Agricultural Sciences & Natural Resources examined four bale feeder designs: a conventional open-bottom steel ring, a sheeted-bottom steel ring, a polyethylene pipe right and a modified cone feeder with a sheeted bottom.

The findings indicated that using a cone-style feeder or modified cone feeder with a sheeted bottom should reduce hay waste to approximately 5-6% of the original bale weight.

"We found that open-bottom hay feeders can waste as much as 21% of the original bale weight," Lalman said. "Unfortunately, one of the most common types of hay feeders on Oklahoma livestock operations is the open-bottom round bale feeder."

Division scientists discovered that differences in hay feeder design do not restrict dry matter intake by the cattle but can significantly affect the amount of feed wasted and, subsequently, the amount of hay fed.

"Feed cost is the single largest variable influencing profitability of a cow/calf enterprise," Lalman said. "Costs associated with nutrition have been shown to contribute between 40% and 60% of the annual budget of a typical cow/calf operation."

State cattle operations already suffering under tight profit margins cannot easily weather such costly waste, especially during years such as 2011, when additional feed costs were a major contributing factor to approximately $668 million in drought-related livestock production losses.


Benefits of early weaning

It pays to wean calves early when severe weather conditions like drought hinder beef cattle production, USDA studies have found.

During drought, limited forage for livestock grazing can restrict calf growth, resulting in lighter calf weaning weights. Drought may also cause cows to lose bodyweight and may weaken their immune functions, reducing their overall health and reproductive performance.

Animal scientist Richard Waterman at the ARS Ft. Keogh Livestock & Range Research Laboratory in Miles City, Mont., examines management options to minimize the effects of severe drought on rangeland livestock production.

Working with local ranchers, Montana State University scientists and American Simmental Assn. collaborators in Bozeman, Mont., Waterman evaluated the early weaning of beef calves and its impact on cow, heifer and steer performance.

Calves at two locations in Montana — Judith Gap and Ft. Keogh — were weaned early at 80 days of age and at the more traditional age of 215 days.

Cows that weaned a calf early weighed more and were in better body condition at the start of winter. As a result, the amount of harvested feedstuffs required for cows to maintain satisfactory bodyweights and condition throughout winter was reduced.

Waterman confirmed that early weaning is a viable management option, presents fewer problems and allows producers to better control their production environment. He also demonstrated that early weaning increases the likelihood that heifers will become pregnant on time in the following breeding season.

Additional studies showed that early-weaned steers reached maturity sooner than traditionally weaned steers when weight gain, feedlot performance and carcass traits were measured.

Waterman noted that management of early-weaned steers can directly affect how they grade at harvest. In some cases, early-weaned steers had poorer USDA yield grades because their carcasses were too fat.

However, Waterman demonstrated that producers can maximize the carcass value of early-weaned steers if the animals are identified before they enter the feedlot and then harvested at an earlier age.

Volume:85 Issue:38

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