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Little Risk Seen from Drug Use in Animals

Despite nearly half a centruy of adding antibiotics to livestock rations, the risk of antibiotic resistance in humans from animals remains extremely slight.

An independent expert group has concluded that while a theoretical threat to human health exists from the use of antibiotics in food animals, the actual risk remains very small.

Those findings come from human microbiologists, risk assessors, veterinarians and animal health experts.

“In 50 years of antibiotic use in animals and man, the development of resistance in animals has not made a major impact on human and animal health, and seems unlikely to happen overnight now,” says Ian Phillips, M.D., University of London.

Phillips chairs the group of experts evaluating the science behind antibiotic resistance. He says the use of antibiotics in humans and animals undoubtedly leads to resistance, and some resistant organisms reach man via the food chain. However, little harm occurs from resistance, even from infection.

The argument against antibiotics used in growth promotion has been based largely on antibiotic-resistant enterococci, bacterial organisms that cause no disease in animals but can cause infections in man. New surveillance data shows resistance is increasing despite the ban on antibiotic growth promoters from use in animals, says the Animal Health Institute (AHI).

European Experience

The move in the European Union to ban antibiotic growth promoters in animals has not cured antibiotic-resistant bacteria in humans. And it has harmed animal health, according to the National Pork Board research group who toured Europe recently.

“Danish farmers have found that banning antibiotic growth promoters has caused pigs to get more cases of diarrhea, especially baby pigs,” states John Waddell, DVM, Sutton, NE. “The pigs have slower postweaning growth rates and increased production costs.”

Denmark completed its ban on Jan. 1, 2000. To compensate, Danish producers increased weaning ages of pigs to four weeks.

Health challenges also resulted in Danish farmers nearly doubling their use of therapeutic levels of antibiotics in pigs (Figure 1). And, they increased supplementation of zinc oxide and copper sulfate to reduce diarrhea problems in the nursery and enhance performance, says Waddell.

“At the same time, human cases of salmonella and campylobacter have reached record levels in Denmark and the proportion of multiple antibiotic-resistant salmonella DT104 has doubled since 1997,” he observes.

Results are nearly identical in other EU countries, including Sweden, France, Holland, Germany, Switzerland and the United Kingdom, says AHI.

Pork Board research group member and Illinois pork producer Jill Appell pointed out that death loss in Danish pigs before the ban was about 1%, after the ban it climbed to around 3%. Most farms in Denmark that were single site and continuous flow have had to change to all-in, all-out pig flow to survive.

Another research group member, Helen Jensen of Iowa State's Center for Agricultural and Rural Development, projected the cost of the antibiotic ban in Europe at a minimum of $1.50/pig. Waddell says a similar ban in the U.S. would add $10/pig to production costs.