by Heather Smith Thomas

Use of antibiotics in animals is a hotly debated issue in human health. There is concern that overuse of antibiotics for treating or preventing disease in humans or animals is leading to resistant strains of pathogens that may not be readily controlled by these drugs. This leads to questions about use of antibiotics in animals, and whether veterinarians and livestock producers are overusing drugs that could become less effective. Use of these drugs in food animals is being scrutinized most, with controversy over use of low level antibiotics in livestock feed.

Dr. Kenny Brock, DVM, MS, PhD, professor at Auburn University (Auburn, Alabama) says, "We should be concerned about antimicrobial resistance. When we use an antibiotic, we're not creating mutant microbes, but are selecting for organisms that have an advantage (since these are the ones that survive). If they've developed or acquired a resistance to a drug we are using, we are selecting for those organisms."

"In food animals, many people worry about residues, but that's a different issue. We have laws and practices to help livestock producers avoid residues (not using a drug within a certain length of time before slaughter, to make sure all traces are gone from the body of the animal).

"The issue of antibiotic resistance involves the resultant increase in a background level of resistance in the population that then becomes a problem when those antibiotics or similar ones are used in humans. This problem, at least in cattle, has not been documented; there has been no direct link found between use of an antibiotic in a beef animal and compromised effectiveness. There have been studies in swine and poultry, but no documented problems.

"But that's not to say we needn't be concerned about it," he says.

"Stricter regulations have come into place in the last 10 years concerning use of antibiotics; we have tightened our usage by label, residue avoidance, injection sites, etc. We have a good education program to help producers do a better job. The problem is being addressed, but it will be a continuing challenge. When we use certain antibiotics we must be sure we have justification for using them," says Brock.

Regarding use of low level antibiotics in feed, this issue is not well understood by the general public. "Most of those drugs are things like neomycin (which stays in the gut, not absorbed into the body), and tetracyclines. They do not present a major problem for resistant pathogens in humans," he says.

"There's always a background level of resistance, and it's questionable whether we are selecting for or increasing that background by our use of antibiotics. Just because we are feeding antibiotics doesn't mean they are causing a problem."

Eventually beef producers may be forced to stop using antibiotics, because of public pressure. If a special interest group wants it halted and makes enough ruckus, there may be laws passed against antibiotic use even if perceived dangers are not proven. "If we don't respond to this issue effectively, the beef industry will lose out," says Brock.

"There is a lot of finger pointing about antibiotic use. Many people point to medical doctors who prescribe antimicrobials such as ampicillin and amoxycillin for everything." This has been a much larger problem for human health than use of antibiotics in food animals--the treatment of humans with antibiotics for every little illness, and human patients discontinuing medication too soon, when they start to feel better. This allows more chance for antibiotic resistant strains of microbes to develop.

The beef industry will sacrifice some efficiency if antibiotic use is banned. "The main benefit of antibiotics is probably in the feedyard, in greater feed gains and prevention of rumen abscesses."

Some antimicrobials used in animals are not used at all in humans, and there is no reason to halt their use. Rumensin, for instance, is technically an antibiotic--used to alter the microbe population in ruminants to prevent bloat and increase digestive efficiency.

With controversy over antibiotic use, however, there is the possibility of losing these tools. "The beef industry should not stay silent when other groups are making noises about banning these uses in food animals." Those groups should be forced to show some real data, and should also recognize studies that refute the perceived dangers, he says.

The beef industry began using antibiotics soon after they became available--first as treatment of sick animals, and later for more efficient feed utilization and faster growth. "Increase in gains is probably the most useful tool. Rumen additives to stimulate bacteria in the rumen led to trying different things, and discovering which ones worked well."

He says this issue should not be ignored. "We definitely should not ignore the people on the other side of the fence that are screaming about it. We need to show that we are concerned and are conscientiously using antibiotics in the proper way." ©