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Antibody Product Eyed for Replacing Antibiotic Supplements in Feed 

Chicken farmers may soon have new ways to help little chicks grow into big chickens without using antibiotics as feed supplements.

Faced with a continuing controversy over antibiotics in animal feeds contributing to the development of drug resistance among microbial pathogens, some researchers are working to develop alternative feed supplements for farm animals, including commercial poultry flocks. One promising new approach focuses on the peptide hormone cholecystokinin (CCK), which helps to control digestion in the intestinal tract of vertebrates, according to microbiologist and animal scientist Mark E. Cook of the University of Wisconsin—Madison. He and his collaborators pioneered a technology, which is being commercialized by DCV, Inc., in Wilmington, Del., that blocks CCK's usual appetite-suppressing properties and thereby accelerates weight gain in chickens. 

When CCK is blocked by a CCK-specific antibody, treated chickens gain weight more rapidly, even though they do not eat more feed. Ordinarily, when CCK is secreted, it increases contractions of the intestinal tract, propelling partly digested foods containing nutrients through it rather quickly. However, treating chickens with the CCK antibody “slows gut motility, so food stays in the intestinal tract longer, and more nutrients are absorbed,” explains Cook. 

Cook and his colleagues make the CCK-targeted antibody by immunizing laying hens, which produce high titers of the antibody in their egg yolks. The antibody-rich yolks are harvested and spray dried without further extraction or purification. When the dried yolk powder containing a concentrated source of the CCK antibody is fed to broiler chickens, growth rate and feed efficiency improve. Poultry producers who want to eliminate antibiotics can now do so without sacrificing their growth benefits, says Cook. “We're seeing more and more companies in the poultry industry who want to move away from antibiotics.”

In 1989, Cook began searching for ways to improve feed efficiency in chickens that did not target microbes or suppress the immune system. Once he focused on the CCK approach and developed an antibody that interferes with its activity in the intestinal tract, “many, many hurdles had to be overcome,” he says, pointing to scaling-up efforts for the technology for coating chicken feed pellets with the antibody as one of the most challenging of those hurdles. Only 100 to 200 grams of the egg yolk powder are needed per ton of feed, and this small amount of material needs to be evenly distributed through the bulk of the feed. “A lot of engineering design inventions had to take place to make this a reality,’ says Cook. 

In 1996, DCV, Inc. (formerly DuPont ConAgra Visions) took over the scale-up challenges and named the antibody-rich egg yolk powder Ovation. A number of field trials in different geographic locations involving millions of chickens show that Ovation improves feed efficiency and weight gain as well as growth-promoting antibiotics do. Typically, individual broiler chickens gain one pound (454 g) while consuming 5 to 8% less feed, translating into a projected savings of $16 million for the U.S. poultry industry. 

“Ovation is not a therapeutic product and will not cure or prevent diseases a broiler may get,” says veterinarian Jeffrey Hunchar, an animal health and nutrition expert at DCV, Inc., but it can replace the routine use of antibiotics used to promote growth. Poultry producers can even use Ovation and antibiotics together. “They're additive and don't interfere with each other,” he says. 

Some producers may choose to use both products, but “many want to get rid of antibiotics to cut costs and market chickens as antibiotic-free,” Cook says. Legislation may also follow the trend in Europe, where many growth-promoting antibiotics are banned. “They're looking for alternatives there,” he adds.

The CCK antibody can also be used in the swine industry. “CCK is very conserved across all animal species,” says Cook. Cattle present more of a challenge because the antibody will need to be packaged to survive transit through the bovine rumen. Cook has patented the egg yolk technology for making antibodies to other peptides that stimulate or inhibit food intake in animals and humans. He also is perfecting an antibody to an intestinal enzyme that improves growth rate in chickens even better than the CCK antibody. “That will be a future generation product,” Cook predicts. According to Hunchar, DCV, Inc. plans to complete field-testing of Ovation and commercialize the product by the end of 2001. 

Carol Potera 
Carol Potera is a freelance writer in Great Falls, Mont.