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January 5, 2001

Disease-resistant bull
cloned at Texas A&M

This bull calf, named 86², is the genetic clone of a bull resistant to tuberculosis, brucellosis and salmonellosis.

By Mike Barnett
Editor

The idea of developing lines of disease-resistant cattle has been pretty well pooh-poohed by most researchers over the years. That is, until now.

The announcement in late December that a bull calf has been successfully cloned from a bull resistant to tuberculosis, brucellosis and salmonellosis, coupled with new gene identification techniques, has sent quivers of excitement down the backs of the animal science community.

The calf, named 86² (squared), due to his expotential genetic potential, researchers say, was born three years after the death of his donor, Bull 86, who was found to be naturally resistant to brucellosis, and under laboratory conditions, resistant to tuberculosis and salmonellosis.

In 1985, cells from the tip of Bull 86's ear were frozen for future genetic study. Fifteen years later, Drs. Taeyoung Shin and Mark Westhusin, from the Experiment Station and the College of Veterinary Medicine, were able to clone Bull 86.

For the first time, this breakthrough could make it practical for animal scientists to develop lines of livestock resistant to infectious diseases. Developing disease-resistant crops is old hat for plant breeders, where short generation-intervals make it practical to test crosses and backcrosses.

However, the same doesn't hold true for livestock. For example, the gestation period for a calf is 283 days. Add at least another year-and-a-half to two years until that calf reaches sexual maturity. Then that animal has to be bred. And then his offspring have to be tested.

That type of time-consuming research is rare in the animal science world, but it is the type that Drs. Gary Adams and Joe Templeton started in 1979 that identified the disease-resistant Bull 86.

"When Dr. Templeton and I began our studies, we were ridiculed for selecting animals for resistance to infectious diseases," Dr. Gary Adams said. "However, with this technology, we can leapfrog much faster to bring those genetically-resistant animals to population level by using semen, artificial insemination, that can be disseminated rapidly.

"Given the idea that we can use genetic resistance to infectious diseases in domestic food-producing animals will have a major impact now in the U.S., Texas and worldwide," he predicted. "There's beginning to be an awakening about the use of this technology and identifying disease-resistant animals as one more way to reduce infectious diseases in our food supply."

Benefits are many

Benefits, of course, will not be immediate. The calf still has to mature and a lot of research still needs to be conducted. But according to Dr. Templeton, Texas A&M researchers will soon have the equipment to sequence a large part of 86²'s chromosomes. So far, seven to eight genes in the calf have been identified that are unique in resistance to the three diseases. Researchers predict near 100 will be found.

"What's critical about that," Templeton said, "is we identify genes in him—he's the benchmark to identify those genes for natural resistance in other cattle. We'll use him to identify cattle that are naturally resistant in other breeds.

"For instance, he (86²) is not a milk breed," he continued. "We need to have a milk breed that's actually resistant, besides beef breeds. So we'll benchmark this and that's working fantastic. That's not speculative and that's not wishful thinking or science fiction. It's true. It's working very well."

The potential impact of disease resistant lines of cattle is enormous. Consider these reflections of TAMU researchers:

•In countries where they are unable to pasteurize milk to kill bacteria or process meat appropriately, breeding disease resistant cows could greatly contribute to a safer food supply, especially pre-harvest.

•The potential to combine natural disease-resistance with the outstanding production traits of U.S. cattle increases the value of U.S. cattle in the world market.

•The potential to purposefully breed a natural resistance to brucellosis and tuberculosis would be an important addition to current disease control methods that have not been 100 percent effective in the United States and abroad.

•This research could benefit ranchers in countries who cannot afford to vaccinate or test their cattle for these diseases. These unprotected cattle are a potential reservoir for re-infection of herds in Texas and the United States.

Cloning's broader impact

Dr. Mark Westhusin said cloning in general is still a very inefficient science. But he stressed it's efficient enough at today's level where scientists can predict at "some pretty consistent level that there are certain animals that we can, in fact, clone."

"I guess the best way to think about that, is, if you have a particular bull, as in this case, where he has a unique genetic endowment and has such a significant value, the time and effort and cost can be significant, but it is certainly worth the significance," he said.

"We're not at the point where we can start mass producing feedlot steers because we can predict that those steers are going to gain six pounds a day...," he continued. "We're not at that point yet, but we'll get there. There's no doubt in my mind."