Texas livestock health officials are increasing disease surveillance for cattle tuberculosis (TB), and one of the targets is Mexican-origin roping steers.

"Texas is at a particular risk for cattle TB, because, each year, livestock brokers import nearly a million feeder cattle from Mexico, where cattle TB is still a serious problem. A number of these Mexican-origin steers are selected for roping practice, competitions or rodeos. Between events, these animals, which often have a four- to five-year life span, occasionally are commingled on pastures with local cattle herds, including calves that may later become Texas feeder cattle," said Dr. Linda Logan, Texas' state veterinarian and executive director for the Texas Animal Health Commission (TAHC), the state's livestock health regulatory agency. Dr. Logan also pointed out that these Mexican-imported roping steers sometimes are in close proximity to dairies, breeding operations and other at-risk animal populations.

"Although Mexican-origin cattle are tested for cattle TB prior to entering Texas, there's always a possibility that the animals were exposed to TB bacteria shortly before importation. In this scenario, the cattle would be incubating infection and not test positive for the disease," she explained. "To reduce this potential risk for disease introduction, we are strictly enforcing TAHC regulations that require Mexican-origin roping steers to undergo a retest for cattle TB prior to entering competition and annually thereafter."

Dr. Logan explained that the cattle TB skin test must be conducted by an accredited veterinarian, who injects tuberculin into the skin near the animal's tail, in an area called the "caudal fold." The veterinarian examines the site 72 hours later for swelling that might indicate that the animal had been exposed to TB. If the animal has no response, the accredited veterinarian will provide the owner with a document that can be presented as proof of testing.

If, however, swelling, thickening or a lump is detected on the "caudal fold" test, a second skin test must be run on the animal's neck by a state or regulatory veterinarian. The animal is free to move if this second test, called a "comparative cervical" is negative. A positive response on the "comparative cervical" test, however, is a strong indication the animal may have cattle TB. The animal must be slaughtered and its carcass carefully examined for internal TB lesions. Tissue samples are collected and forwarded to the National Veterinary Services Laboratory (NVSL) in Ames, Iowa for laboratory confirmation.

Since summer 2001, two of Texas' 153,000 domestic cattle herds have been diagnosed with cattle TB, and the U.S. Department of Agriculture will cancel the state's TB-free status in early June. "We can get our 'free' status reinstated in two years, but only if we find the last of any infection and conduct tight disease surveillance," Dr. Logan pointed out. "We cannot provide 'zero risk' in a global trading environment, but by re-testing and ensuring that imported animals are disease-free, we can reduce disease risks for Texas livestock producers."