Pigs with worms typically show a combination of poor weight gain, changes in their manure, a rough or dull hair coat, and a potbellied appearance despite not growing well. Some infections also cause persistent coughing. The tricky part is that light worm burdens often produce no visible signs at all, so knowing what to watch for and when to test is essential for catching a problem early.
The Most Common Physical Signs
The clearest indicator of a worm problem is a pig that eats but doesn’t thrive. Parasitized pigs gain weight roughly 31% slower than uninfected pigs, according to a large meta-analysis of swine parasite studies. They also eat about 5% less feed overall, and the feed they do consume converts to body weight far less efficiently. So if your pig seems to be eating a reasonable amount but looks thin, bony, or undersized for its age, worms should be near the top of your list.
Other physical signs to look for:
- Potbelly with a thin frame: A distended belly paired with visible ribs or hip bones is a classic parasite look, especially in younger pigs.
- Rough, dull hair coat: Healthy pigs have smooth, somewhat glossy hair. A coarse, bristly, or patchy coat suggests the pig isn’t absorbing nutrients properly.
- Pale skin or gums: Some worms, particularly whipworms, cause blood loss that leads to anemia. If your pig’s gums or inner eyelids look pale rather than pink, that’s a red flag.
- Visible worms in manure: Heavily infected pigs sometimes pass whole roundworms in their stool. These look like thick, cream-colored spaghetti and can be several inches long.
Changes in Manure
Your pig’s manure is one of the best early warning systems for worms. Normal pig manure is firm to moderately soft with a consistent color. Worm infections change that in specific ways depending on the parasite involved.
Whipworms are particularly destructive to the large intestine. Loose to watery diarrhea typically begins about two to three weeks after infection. As the larvae mature and burrow into the intestinal wall, you may notice mucus and blood in the stool. In severe cases, the diarrhea becomes frankly bloody, a condition similar to dysentery. Young pigs are especially vulnerable, and bloody diarrhea from whipworms can be fatal if untreated.
Large roundworm infections don’t always cause dramatic stool changes, but you may notice manure that’s looser than usual or contains whole worms. If you see anything that looks like a worm in the manure, save a sample in a sealed bag or container. Your vet can identify it and recommend the right treatment.
Coughing and Breathing Problems
Not all worm symptoms show up in the gut. Several pig parasites spend part of their life cycle in the lungs, and this migration causes respiratory symptoms that can look a lot like pneumonia.
Large roundworm larvae hatch in the small intestine and travel through the bloodstream to the lungs before being coughed up and swallowed again. During this lung phase, pigs may develop a dry cough, wheezing, or labored breathing sometimes called “thumps,” a rhythmic, heavy breathing pattern visible in the pig’s flanks. This stage can mimic asthma or pneumonia, and it’s easy to mistake for a respiratory infection rather than a parasite problem.
Lungworms cause a more persistent cough that can last weeks. The hallmark is a chronic cough that sometimes comes in fits, getting noticeably worse with exercise or stress. Young pigs are more likely to show clinical signs, while older pigs may carry lungworms with only a mild, occasional cough. If a bacterial or viral respiratory infection hits at the same time, which is common, the symptoms become significantly worse.
Less Obvious Worm Types
Kidney worms are a less well-known parasite that damages the kidneys over time. Because the destruction happens internally, signs can be subtle: poor appetite, gradual weight loss, and general weakness. The pig’s body struggles to clear metabolic waste when kidney tissue is compromised. Kidney worm eggs are shed in urine rather than feces, so a standard manure test won’t catch them. If kidney worms are suspected, a urine sediment test can detect eggs with high accuracy.
How to Confirm Worms With Testing
Physical signs can point you toward a worm problem, but they can’t confirm it or tell you which parasite you’re dealing with. A fecal egg count is the standard diagnostic tool. The test uses a flotation solution that separates parasite eggs from the rest of the manure, causing the eggs to float to the surface where they can be counted under a microscope.
To get a useful sample, collect fresh manure (ideally less than a few hours old) directly from the pig or from a spot you saw the pig use. Place two to three tablespoons in a sealed plastic bag, label it with the pig’s ID, and refrigerate it if you can’t get it to a vet the same day. Don’t freeze it.
The vet will mix a measured amount of manure with flotation solution, strain it, and examine it on a special counting slide at 10x magnification. The result comes back as eggs per gram (EPG), which tells you not just whether worms are present but how heavy the burden is. A low count might mean the pig can manage with monitoring, while a high count calls for immediate treatment.
One important caveat: fecal egg counts only detect adult worms that are actively laying eggs. If larvae are still migrating through the lungs or liver, the test can come back negative even though the pig is infected. If your pig has respiratory symptoms or other signs but a clean fecal test, it’s worth retesting in a few weeks.
Which Pigs Are Most at Risk
Young, growing pigs are more vulnerable to worm infections than mature adults. Their immune systems are still developing, and even a moderate parasite load can significantly stunt their growth. Pigs raised on pasture or dirt lots face higher exposure than those on concrete, because most worm eggs survive and develop in soil. Pigs that root in dirt, which is essentially all of them given the chance, are constantly encountering parasite eggs.
Breeding sows are another high-risk group. They can harbor low-level infections without obvious symptoms and pass worms to their piglets through contaminated environments. Deworming sows before they farrow helps break this cycle.
Preventing Reinfection
Deworming treats the current infection, but pigs will pick up worms again if the conditions that caused the first infection haven’t changed. A few practical steps make a real difference.
Rotate pastures when possible, since parasite eggs accumulate in soil over time. Clean pens and sleeping areas regularly, because manure buildup is the primary source of reinfection. If you’re raising pigs on pasture, avoid overcrowding the same ground year after year. For breeding stock, deworming before breeding and again before farrowing keeps egg shedding low during the periods when piglets are most vulnerable. Growing pigs benefit from at least one deworming during their growth phase, timed based on fecal egg count results rather than a fixed calendar.
Keeping records of fecal test results over time helps you spot trends. If egg counts climb despite treatment, you may be dealing with a resistant parasite population or a management gap that’s allowing rapid reinfection.