A herd of cattle or a flock of chickens may appear very bucolic, but they're actually ground zero for an ongoing arms race between scientists and disease-causing bacteria. Antibiotics have been a major weapon in the fight against animal infection, but they've also sparked evolutionary forces that create drug-resistant bacteria that render those very antibiotics ineffective, posing a major risk to animals and humans alike. Now a University of Wisconsin-Madison team is developing a method of fighting a major group of animal infections without antibiotics.

Antibiotics have been a tremendous boon to animal husbandry as they prevent losses of livestock from once common infections that could bankrupt farmers and even cripple national economies. Small wonder that 80 percent of antibiotics in the United States are used on farm animals to protect against disease and promote growth. However, this has proved to be a double-edged sword because such heavy use kicked off an evolutionary arms race against these medicines. It's one reason why some antibiotics have become less effective against certain resistant strains and why doctors have kept some antibiotics in reserve against future needs.

The problem is how antibiotics work. Tailored to interfere with the biochemical mechanisms of microbes and parasites, they disrupt enzymes or attack the membranes of bacteria. It's effective, but it's also exactly the sort of thing that kicks natural selection into top gear; producing a new super germ, which can spread to other farms and the general population, but does not respond to antibiotics.

A team led by Mark Cook, a professor of animal sciences, attacked this problem by turning it around. According to Cook, microbes evolve so quickly, an antibiotics arms race is a losing proposition, so instead of going after the microbes, Cook's team addressed an ancient weakness in the animals that the microbes exploit. Normally, an animal's immune system can see off an infection, but a surprisingly diverse group of organisms, including bacteria, single- and multi-celled parasites, protozoa, and some viruses produce a chemical known as macrophage Migratory Inhibition Factor (MIF). This triggers an "off switch" in the animal's immune system called Interleukin 10 (IL-10), which allows the pathogen to slip by and attack without triggering a counterattack.

Cook's approach was to create a vaccine by introducing an antibody to IL-10 in hens' eggs, which could then be introduced into animal feed. According to the UW-Madison team, the antibody works in the gastrointestinal tract and marks the first time this kind of immune system manipulation has been used in such an area.

The largest experiment included 300,000 chickens, which became fully immune to coccidiosis, a major farm animal infection that takes hold inside the intestine. Another test where beef steers were fed the antibodies for two weeks cut the rate of bovine respiratory disease in half, while newborn dairy calves treated for 10 days showed similar results.

Another UW-Madison professor of animal science, Dan Schaefer, plans a larger bovine trial with other universities in the near future. Meanwhile, one of the four patents filed by Cook and his team has just been granted and they are turning the research into a commercial enterprise called Ab E Discovery LLC.

"We are not focused on the pathogens," says Cook. "We are focused on what they are trying to do to the immune system. We are getting encouraging data from dairy and beef. We have conducted experiments involving 300,000 chickens in commercial farms, half receiving the product. We know it works. The market is interested, and now it's a matter of making a product."