Extension Notebook: What’s that smell? The hidden language of pigs

Walk into just about any pig barn, and one of the first things you’ll notice is the smell. Every barn has that familiar, unmistakable swine odor. Most people don’t think much of it, but what if there’s more to that smell than we realize? Behind that familiar barn smell lies a hidden language of chemical signals that influence how pigs communicate, behave, reproduce, and respond to their environment.

Pigs communicate through chemistry. Pigs rely heavily on their sense of smell. One way they communicate is through pheromones, chemicals released by one animal that influence the behavior or physiology of another animal of the same species.

In the breeding barn, boars release pheromones through their saliva that stimulate reproductive behaviors in sows that are in heat. Researchers have identified three important molecules involved in these responses: androstenone, androstenol, and quinoline.

By recreating these chemical signals, synthetic boar pheromone products can help producers identify sows in heat, including those whose signs might otherwise go unnoticed. These products offer another tool for improving heat detection and breeding efficiency while reducing direct contact with live boars, which can present safety, labor, and biosecurity concerns. Live-boar exposure also helps stimulate puberty in replacement gilts. Researchers are exploring whether synthetic pheromones could provide similar benefits for gilt development and breeding management.

Chemical communication also plays an important role between sows and their piglets. Shortly after birth, piglets learn to recognize their mother’s scent, which helps guide nursing behavior. At weaning, everything changes. Piglets lose that familiar scent while adjusting to new surroundings, unfamiliar pen mates, and solid feed. But what if we could bring some of that maternal familiarity into the nursery? That’s exactly what we’ve explored using maternal pheromones. In our research, newly weaned pigs exposed to these chemical cues fought less, spent more time eating, and gained more weight. For producers, this offers an opportunity to create a calmer nursery, ease the transition after weaning, and improve piglet performance with little additional labor.

Chemical information may tell us more than how pigs communicate. It may also reveal clues about their health. Some experienced livestock caretakers say they can smell when animals are getting sick. But what if we could detect disease before the first cough, or even identify which illness is developing? Infection changes an animal’s metabolism, altering chemicals released through its breath, skin, and waste. Some of these chemicals, called volatile organic compounds, enter the surrounding air. Researchers are investigating whether different diseases produce distinct chemical patterns, much like fingerprints. Preliminary research involving pigs infected with porcine reproductive and respiratory syndrome (PRRS), a costly viral disease, detected changes in airborne chemicals before obvious signs of illness appeared.

At the University of Illinois, our research team is exploring whether these chemical patterns, combined with changes in pig behavior, could help identify PRRS earlier and distinguish it from other health conditions. Imagine monitoring barn air for early warning signs of disease, giving farmers time to investigate, consult their veterinarian, and respond sooner. Although still experimental, this approach could become a valuable tool for protecting herd health.

Not every odor is a pheromone, but understanding the chemical signals pigs produce opens new possibilities for improving animal welfare, health, and farm management. The next time you walk into a pig barn and notice that familiar smell, think about what the pigs might be sensing. To us, it may just smell like a barn. To a pig, the air is full of information.

Courtney Archer, Ph.D., is an assistant professor and swine Extension specialist, University of Illinois Urbana-Champaign.