As mounting research has shown how antibiotic-resistant bacteria can affect public health, the Food and Drug Administration (FDA) has been hardening its stance on the use of antibiotics among the animals we eat. But when it comes to dairy cows, the ones that give us milk, cheese, and yogurt, it’s an entirely different ballgame. These cows are only given antibiotics when they’re sick, as the antibiotics appear in their milk almost immediately. If a truckload tests positive for the drug residue, it’s rejected for violating food safety rules. These rules have substantially improved the safety of milk and its production, albeit with a few concerning hiccups, a new FDA report shows.

The report, which looked at 1,912 milk samples, found that overall, our milk supply is indeed safe. About half of the farms (953) were considered the “targeted” group due to previous violations, which involved detectable drug residues in their cows’ tissue while being sold for slaughter. The FDA tested all the samples for 31 different drugs, consisting mostly of antibiotics but also including an antihistamine and non-steroidal anti-inflammatory drugs.

When it came to the targeted group, the agency found that 11 samples contained drug residues higher than the maximum allowable limit, with one sample containing two drug residues. Only four of the 959 non-targeted samples were confirmed positive for drug residues. While this only amounted to 1.15 percent of the targeted samples and 0.4 percent of the non-targeted ones, none of the six drug residues the FDA found are tested for when trucks of raw milk arrive at a dairy plant. In fact, none of them had ever been approved for use in lactating dairy cows, meaning their use is illegal.

According to the report, two of the six drugs found in the targeted group (sulfamethazine and ciprofloxacin) are illegal even for “extralabel” use in dairy cows. The other four (florfenicol, gentamicin, tilmicosin, and tulathromycin) are permissible only under certain strict conditions — these drugs’ have to undergo a withdrawal period so their residues won’t show up during testing, for example.

Speaking optimistically, Dr. William Flynn, deputy director for science policy in the FDA’s Center for Veterinary Medicine, said, “Overall this is very encouraging and reinforces the idea that the milk supply is safe,” according to The Associated Press.

Because of the study’s double-blind design, the samples were taken randomly with no way to trace the ones with residue back to their farms. But according to the report, the findings will help the agency develop new safeguards, such as testing for a wider range of drugs, collaborating with state regulatory agencies to educate dairy producers, and possibly collecting milk samples when illegal residues turn up on a case-by-case basis.

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