Treating worms in pigs starts with identifying the type of parasite involved, then choosing the right dewormer and adjusting your management practices to prevent reinfection. Most pig operations deal with large roundworms, whipworms, lungworms, or nodular worms, and each responds to a slightly different approach. The good news is that a small number of widely available dewormers cover nearly all of them.
Common Worms and What They Look Like
The large roundworm is by far the most common internal parasite in pigs worldwide. Many infected pigs show no obvious signs, which is part of what makes the problem easy to miss. In heavier infections, you may notice slow weight gain, a generally unthrifty appearance, and sometimes whole worms passed in manure. Young pigs with migrating larvae can develop a labored breathing pattern sometimes called “thumps.”
Whipworms live in the large intestine and cause watery or bloody diarrhea, poor feed conversion, and weight loss. Nodular worms burrow into the intestinal wall and create small nodules that damage the gut lining. Lungworms produce a persistent, sometimes severe cough that worsens with exercise or stress. In a pasture-raised herd, it’s common for pigs to carry more than one species at once.
When to Treat: Using Fecal Egg Counts
Rather than deworming on a fixed calendar, many producers now use fecal egg counts to decide when treatment is actually needed. A veterinarian or diagnostic lab examines a manure sample under a microscope and reports the number of parasite eggs per gram (epg). For young pigs up to about four or five months of age, any result over 50 epg may warrant treatment, because young animals can harbor significant worm burdens while shedding relatively few eggs. For older pigs, counts under 100 epg are generally not a concern.
This targeted approach saves money, reduces unnecessary drug use, and slows the development of drug-resistant worm populations. It also tells you which parasites you’re dealing with, since egg shape under the microscope varies by species.
Choosing the Right Dewormer
Two drug classes handle the vast majority of pig worm problems: the benzimidazoles (fenbendazole being the most common) and the macrocyclic lactones (ivermectin and doramectin). Both are effective against roundworms, nodular worms, and lungworms. Whipworms require a benzimidazole; ivermectin alone won’t reliably clear them.
Fenbendazole (Feed-Based)
Fenbendazole is mixed directly into feed, which makes it the easiest option for group treatment. The FDA-approved protocol calls for it to be fed as the sole ration for 3 to 12 consecutive days, delivering a total dose of about 9 milligrams per kilogram of body weight. For lungworms specifically, the treatment window runs the full 3 to 12 days. This broad spectrum and ease of administration make fenbendazole a go-to choice for herds with multiple parasite species, including whipworms.
One practical advantage: pigs don’t need to be individually restrained. You simply mix the medicated feed and ensure each animal gets its share. The main risk is that dominant pigs eat more than their portion while timid ones get too little, so watch feeding behavior closely or use individual feeders when possible.
Ivermectin (Injectable)
For swine, ivermectin injection is given under the skin in the neck at a dose of 300 micrograms per kilogram of body weight, which works out to 1 milliliter per 75 pounds. It’s highly effective against roundworms, lungworms, nodular worms, and external parasites like lice and mange mites. This makes it a good dual-purpose option if your herd has both internal and external parasites.
The injectable route does require individual handling, which adds labor but ensures each pig gets the correct dose. An oral premix formulation of ivermectin also exists for in-feed use.
Piperazine
Piperazine is an older, narrower-spectrum dewormer that targets large roundworms specifically. At 200 milligrams per kilogram given orally, it achieves 99 to 100 percent efficacy against roundworms and nodular worms, with egg shedding dropping by 98 to 100 percent within six days. It’s inexpensive and still works well for straightforward roundworm problems, but it won’t touch lungworms or whipworms.
Withdrawal Periods Before Slaughter
If you’re raising pigs for meat, timing your deworming around slaughter dates is essential. Ivermectin given by injection requires an 18-day withdrawal period before slaughter. The oral premix formulation has a shorter 5-day withdrawal. Always check the product label for the most current withdrawal information, as timelines can change with new formulations.
Cleaning the Environment
Deworming pigs without addressing their living space is a losing battle. Roundworm eggs are extraordinarily tough. They survive in soil for years and resist most standard cleaning products. Research on disinfectants effective against roundworm eggs found that povidone iodine solutions (5 to 10 percent), ammonia solution (25 percent), chlorine dioxide, and UV radiation can fully inhibit egg development, but many of these require extended contact times of 30 minutes to several hours. Standard barn disinfectants at typical dilutions often fail.
After treating your herd, clean pens thoroughly by removing all manure and organic matter before applying a disinfectant. On concrete or solid floors, pressure washing followed by a povidone iodine or chlorine dioxide treatment gives the best results. For dirt-floored pens, removal and replacement of the top layer of soil is sometimes the only reliable option.
Pasture Rotation and Long-Term Prevention
For pasture-raised pigs, rotation is your most powerful tool. Many swine parasites survive in soil for a year or longer, so resting a paddock for a single season may not be enough. The goal is to move pigs onto clean ground before the next generation of larvae becomes infective, which typically takes two to four weeks in warm weather.
A few practical strategies that reduce parasite pressure over time:
- Rotate pastures regularly so pigs aren’t grazing the same ground where they deposited eggs weeks earlier.
- Rest paddocks for as long as possible, ideally a full year, before returning pigs to previously used ground.
- Treat new arrivals with a dewormer before introducing them to your herd or pastures.
- Run fecal egg counts two to three times per year to monitor whether your prevention program is working.
- Avoid overstocking, since higher animal density means faster environmental contamination.
A Practical Deworming Schedule
Most small-scale and commercial operations deworm sows about two weeks before farrowing, which reduces the parasite load piglets are exposed to at birth. Growing pigs are typically treated at or shortly after weaning and again at around four to five months of age if fecal egg counts justify it. Boars and replacement gilts benefit from treatment before entering the breeding herd.
The specific schedule depends on your climate, housing type, and parasite pressure. Pasture-raised herds generally need more frequent monitoring than pigs kept on concrete. Running fecal egg counts before and two weeks after treatment tells you whether your dewormer is still working effectively, since resistance can develop over time, particularly if the same drug class is used repeatedly without rotation.