LAURINBURG, N.C. — The swine kidnappers gathered at a North Carolina motel just before dusk.

“Does everyone feel comfortable with the possibility of doing jail time?” Wayne Hsiung, an animal-rights activist, asked his volunteers, among them a barista, a third-grade schoolteacher and a Berkeley undergrad. They nodded.

The risk would be worth it, Mr. Hsiung said, to chip away at unanswerable questions: How widespread is the use of antibiotics on American farms? And how much are these farms contributing to the rise of drug-resistant infections?

Although scientists agree that the heavy use of antibiotics in livestock contributes significantly to the problem of drug resistance, getting details about farmers’ practices is nearly impossible. That’s because farms are not required to disclose to the government how much of the drugs they use, and federal inspectors are barred from making spot checks on farms to determine the prevalence of infections resistant to antibiotics.

In a half-dozen states, so-called ag-gag laws punish those who expose conditions on factory farms.

Industry executives say American pork farmers are good stewards of antibiotics. A two-year-old federal ban on using the drugs for growth promotion has led to a 33 percent drop in their use in livestock. Making further cuts, they say, would only lead to animal suffering.