In a barn outside Manhattan, Kan., researchers from Kansas State University are trying to solve the riddle of bovine respiratory disease. They're sticking plastic rods down the noses of six-month old calves, collecting samples of bacteria.
"This bacteria, Mannheimia haemolytica, lives in most cattle," explains Mike Apley, one of the research leaders. Sometimes, for reasons that aren't well understood, those bacteria make cattle sick. When that happens, or when it just seems likely to happen, cattlemen deploy antibiotics.
Apley hopes to find out, among other things, whether those antibiotics actually work as advertised. If they don't, he says, it's an easy decision to not use them. Farmers save money and meat industry critics, who want farmers to use fewer antibiotics, are happy, too. "It's a win-win for everyone."
Unfortunately, when it comes to antibiotics on the farm, it's not always a win-win. And when there's a fight, veterinarians are right in the middle of it, pushed back and forth by conflicting loyalties.
To understand those pressures, I paid a visit to veterinarian Steven Henry in Abilene, Kan. Henry is a leading swine specialist.
Pork producers rely heavily on veterinarians like Henry for advice. "They don't want to spent money on drugs if they don't need to," says Henry. "Now, you have to juxtapose that with a tremendous amount of pressure from pharmaceutical companies to move product."
Those companies aim advertising campaigns at farmers and veterinarians alike. Henry says he dismisses it, but others are influenced. As a result, farmers sometime use more drugs than they should.
In addition, many veterinarians have a financial interest in such decisions. They re-sell antibiotics to farmers.
"There's some margin in there for the veterinarian, so there's some incentive for the veterinarians to sell more," says Henry.
In Denmark, the government took away that incentive in 1994. It stopped veterinarians from earning profits on such sales. The next year, antibiotic use dropped by almost 25 percent. (The Danish government also banned sales of one antibiotic that year, which may account for part of the decline.) Since then, Denmark has passed other regulations limiting antibiotic use in agriculture.
But Steven Henry says he still trusts veterinarians, more than any regulations by government, to make sure antibiotics are used wisely. When veterinarians enter the profession, in fact, they swear an oath to protect animals and also promote public health.
But they soon develop other loyalties, too above all, to farmers, who in turn are driven by the need to earn a living.
Antibiotics can make meat production more efficient. Some drugs are used to make animals grow faster. Others reduce the risk of liver abscesses in feedlot cattle that are eating energy-rich diets of corn.
Mike Apley, the veterinarian at Kansas State, says those things matter when your clients are struggling to stay in business. "The cost of production is a reality in food animal medicine and food animal production," he says.
Critics of the meat industry, though, say using antibiotics this way is irresponsible.
Any time antibiotics are used, it increases the likelihood that bacteria will evolve resistance to them. Such drug-resistant bacteria can migrate, raising the risk of infections that doctors can't treat as easily.
Michael Blackwell, a veterinarian and former official at the Food and Drug Administration, says it's not acceptable to increase that risk just to produce meat more cheaply. Even if there's not clear evidence of harm right now, it's unwise to wait until it's too late, "when there are literally bodies in the street."
"We have got enough science to know that we need to act," says Blackwell, who also is a leader of the Humane Society Veterinary Medical Association, and a critic of methods used by meat producers. Blackwell says antibiotics should only be used to fight disease, and only at "therapeutic" doses sufficient to kill virtually all disease-causing bacteria.
Kansas State's Mike Apley, for his part, says he's ready to stop advising meat producers to use any antibiotic if he's convinced that it could harm people. But he says the scientific evidence so far doesn't persuade him that's he's doing anything risky.
"I want to fully support human health," he says. "But at the same time, I don't want to remove valuable tools when that removal will not have a benefit for human health." He pauses. "You know, we're really ... It's tough! It's tough!"
It's tough because of scientific uncertainty, and also because veterinarians serve two masters: public health and food production.