Resisting Antibiotic Resistance

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In its March 30 edition, Scientific American put the issue succinctly: “You could not design a better system for guaranteeing the spread of antibiotic resistance.” The “system” the publication was referring to was one that relies on the steady administering of low level, “subtherapeutic” dosages of antibiotics to boost the production of livestock. Attempts to restrict such use of drugs has met with stiff resistance from the livestock industry, which claims it will result in nothing short of economic Armageddon. But the National Pork Producers Council and its ilk are starting to run out of excuses, thanks to Denmark’s experience.

The U.S. Food and Drug Administration estimates that around 80 percent of the antibiotics produced in the U.S. are used in the livestock industry. Numerous studies have shown a significant rise in the growth of antibiotic resistant bacteria in recent decades, an indication that over-use of pharmaceuticals is threatening to return us to the dark ages of pre-penicillin, when people died from even the most basic infections. (It should be pointed out that humans are part of the problem as well—receiving antibiotics for treatment of a viral ailment such as the common cold, for example, is another way we create the perfect environment for spawning drug-resistant super-bugs.)

To get a sense of how ubiquitous this problem has become, check out this paper in Applied and Environmental Microbiology. Scientists report there that mice, voles and shrews living in the vicinity of swine farms were five times more likely to carry E. coli that was resistant to the antibiotic tetracycline when compared to animals living further away from the farms. I have a special fondness for tetracycline—it came to my rescue back in the 1980s when I was struck down by tick bite fever.

No wonder health care professionals are calling for greater restrictions on the use of subtherapeutic dosages of antibiotics in livestock production. The Centers for Disease Control, for one, announced in a November letter that there is a strong connection between antibiotic use in food animals and antibiotic resistance in humans.

But the livestock industry has resisted all attempts to ban or even significantly restrict subtherapeutic use of antibiotics, arguing that it would mean economic disaster for the farming sector. In fact, the industry seems to be populated by a fair number of antibiotic-resistance deniers. Chelsea Redalen, the National Pork Producers Council’s director of government relations, recently stated: “…there is little to no evidence that restricting or eliminating the use of antimicrobials in food-producing animals would improve human health or reduce the risk of antimicrobial resistance in humans.”

Perhaps Redalen needs to read the CDC’s letter and then follow up by paying a visit to Denmark. Since 1995, Denmark has imposed increasingly tighter restrictions on the use of antibiotics in the production of pigs, poultry and other livestock. Today, subtherapeutic use in Danish livestock is banned.

The result? A study of the Danish swine industry from 1992 to 2008 found that the post-subtherapeutic Danish pork industry is producing more pigs per sow, and the average daily gain of those pigs is higher. The mortality rates for weaning and finishing pigs in 2008 were similar to what they were in 1992. In short, the country retained its place as the world’s number one exporter of pork.

These results suggest “that long-term swine productivity was not negatively impacted by a ban on [antimicrobial growth promoter] use,” concluded the study, which was published in the July 2010 issue of the American Journal of Veterinary Research.

A couple of caveats: First, there are indications that therapeutic use of drugs to treat sick animals has gone up in Denmark since the ban. But therapeutic use is much less likely to lead to super-bugs than subtherapeutic use. And Denmark’s overall antibiotic use in all livestock production is still 40 percent lower than when the ban was initiated.

And there were some initial bumps along the way for Danish pork producers in making the transition to dropping subtherapeutics. For one thing, the average weight of newborn pigs fell at first, and mortality rates went up. But then farmers started making adjustments in their animal husbandry techniques. They started leaving the sows and piglets together longer to bolster the litters’ immune systems naturally, and gave the pigs more room to move around.

Some also switched from the use of slatted floors to deep bedding made from straw and other dry material. This latter strategy helps manage waste as a relatively dry material rather than as liquid manure, creating a less stressful environment for the pigs.
The lesson is clear: there is a reason subtherapeutics are used in intensive confinement systems—they help animals deal with the rigors of being crowded onto concrete slatted floors over liquid manure pits.

Production systems that allow animals to live in a more natural environment can help make the crutch of subtherapeutic antibiotics unnecessary. And as we mentioned in this blog a few weeks ago, we’ve got farmers right here in Minnesota who are proving you can raise hogs without subtherapeutics.

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