The Food and Drug Administration last week announced a plan to phase out the use of antibiotics to promote weight gain in livestock - a widespread practice thought to have contributed to the spread of drug-resistant bacteria.

The agency is asking antibiotics manufacturers to indicate on their labels that the drugs are intended only for the treatment or prevention of disease. Traditionally, such drugs have been administered to also make animals grow faster and improve "feed efficiency," meaning they need less food to gain the same amount of weight.

The agency's plan would require that antibiotics be used only with the guidance of a veterinarian, so that a prescription would be necessary. Major manufacturers already have expressed a willingness to comply, the agency says. They would have three years to implement the changes.

When antibiotics are overused, bacteria can develop resistance to the drugs. The concern is that resistant bacteria then could be passed along to humans - either by eating meat from the animals or produce that was fertilized with their manure.

The Inquirer spoke about the issue with Sherrill Davison, director of the Laboratory of Avian Medicine and Pathology at the New Bolton Center of the University of Pennsylvania's School of Veterinary Medicine. 

Question: How long have antibiotics been used to promote weight gain in livestock? 

Davison: We've used them for many years, and I'm going to focus really on talking about poultry. We have used them, but many companies have actually discontinued their use. They really are working collaboratively with the FDA to do that phaseout of those particular antibiotics.

Q: How do antibiotics make animals bigger?

A: I'm not sure we totally know how it works. . . . It helps with the absorption of food.

We know there are other methods and ways of doing this [promoting weight gain] through management with respect to feed. Many of the companies have their own nutritional people looking at feed.

Q: Is it certain that the practice of using antibiotics to promote animal growth leads to the rise of drug-resistant bacteria in humans?

A: I think over the years there's been great debate as to whether that is the case or whether that is not the case.

Whether we're dealing with human medicine or veterinary medicine, we all have to use the rule of judicious use of antibiotics. You really need to have the diagnosis of bacterial infection. Antibiotic use is the responsibility of both human medicine and veterinary medicine. We do take it seriously.

We want to have [antibiotics] as part of the tools that we need to make sure that we can preserve the health of the animals and their well-being, too.

Q: How will veterinarians help to reduce antibiotic use?

A: In the majority of situations right now, that's [already] the case that we're involved. We want to be involved in the decision-making process as to what medicines are given.

Q: The FDA's plan would still allow livestock producers to use antibiotics for disease prevention. That seems like a big loophole.

A: As we go forward, we'll have to define what they mean by disease prevention.

That may mean you have a group of birds. Let's say you have two pens or two houses. And you know this particular one has the problem [of infection]. Will it be allowed, in that other pen, to give the antibiotic so it doesn't spread?

There are very different situations and different industries [with the various kinds of animals].

Q: A consumer already can avoid meat from animals treated with antibiotics by buying organic, right?

A: Some people wish to buy organic and that's perfectly fine.

But whether it's all-natural, whether it's organic, whether it's the normal chain of poultry production . . . I think the important thing is that we in veterinary medicine, we in the animal industries, we are very committed to the production of safe food.