14 January 2000
What came first the antibiotic or the chicken?
by Kate Melville
The last 20 years has seen many countries consumers move away from red to white meat with a huge growth in the consumption of chicken. These changing consumption patterns have been matched by growing consumer unease about how food is produced. One such issue is the use of antibiotics in the rearing agricultural animals (like chickens, pigs and cattle) and whether this may be linked to an increase in antibiotic-resistant bacterial strains. The ever-increasing number of antibiotic-resistant strains means doctors are now struggling to cure some human infections
Many European countries have already banned the routine use of antibiotics in chickens and consumer groups in other countries are pressing governments to take similar action. However at the University of Wisconsin-Madison Mark Cook an animal scientist thinks he has found ways for producers to raise chickens economically but using fewer antibiotics. "I believe that our new tools and strategies will increase both animal and human health," he says.
His work is aimed at slowing the development of antibiotic-resistant bacterial strains, thereby preserving the useful life of antibiotics, and allow scientists to breed chickens with strong immune systems.
Cook believes that the European approach of banning antibiotics would dramatically increase food costs and leave animal producers with few strategies to control diseases. He also believes that this would have a knock-on effect for humans as it may reduce investment in new pharmaceuticals to fight infection in both animals and people.
According to Cook, "To keep birds healthy, we've come to rely on antibiotics, which promote growth by warding off infections and their growth-reducing effects. We need other ways that poultry producers can keep the birds growing rapidly without feeding antibiotics routinely in the diet."
I the 1950's when the practice of supplimenting animal diets with antibiotics began, researchers didn't fully understand why antibiotics improved animal growth. "You might expect that infectious microbes themselves decrease animal growth. Instead, the animal's own immune system is responsible for the growth depression that occurs when an animal is infected," Cook said. "Chickens respond to immune stimulants much the way we do to the flu. They don't want to eat, their muscles begin to break down and they lose weight."
Cook believes this is because when faced with a foreign substance (such as an infectious microbe) the immune system's white blood cells release cytokines. This then cause the gut to produce peptides that result in loss of appetite and promotes muscle wasting in animals.
To test his theory Cook tested two compounds that allow birds to grow just as fast as birds fed antibiotics. The was an antibody , not an antibiotic that binds to gut peptides, thereby reducing appetite loss. So with the antibody, chickens retained their appetites, even when microorganisms were attacking their immune systems. Cook has already patented a method for producing these antibodies in eggs. Egg powder can then be fed to large flocks, thereby improving their feed conversion and growth, but without causing drug-resistant bacteria.
The second compound tested was conjugated linoleic acid (CLA), that was thought to be a compound found in ground beef that inhibits cancer. Cook work indicated that CLA inhibits the message that triggers the breakdown of muscle cells.
But how does this make much of an impact on the problems that are already occurring? Well Cook believes that today's chickens have weaker immune systems, "I believe that by selecting for animals that grow rapidly, we've bred animals with weakened immune systems. Breeders can't now select for birds with strong immune systems because that means selecting for slower-growing animals, which would put them out of competition in the industry."
So by feeding animals antibodies and CLA, as opposed to antibiotics, could allow farmers to selectively breed animals with stronger immune systems. This in turn may lead to animals that are better able to fight off infections thus decreasing the need for antibiotics!