How to Identify Lice on Swine


Lice may often go unrecognized in a swine herd, even though these parasites are widely distributed among herds in the United States. Lice infestation is often not considered a serious problem, but it may lead to economic losses for the producer. It is important for the producer to watch for signs of lice infestation and to be able to recognize these parasites on swine.

About the Insect

The pig louse is known by the scientific name Hematopinus suis and belongs to the suborder Anoplura. It has piercing and sucking mouth parts which it uses to penetrate the pig’s skin and to feed on the pig’s blood and lymph.

Each adult female louse lays about 3-4 eggs (or nits) each day, which she attaches to individual hairs on the pig by a cement-like substance. These eggs will hatch and the baby lice (nymphs) develop through 3 stages or “instars” before they become adults. At each life stage after they are hatched, lice feed on the blood of their host, the pig. The entire lifespan of any louse (from egg to egg) is 23-30 days, and there are always plenty of lice left to take the place of those that die.

How Lice Spreads in a Herd

Lice are spread by direct contact between pigs. For example, sows can pass lice onto their litters and nursery/grower pigs can spread it among themselves. In addition, lice can be spread by something a pig touches (fomite). For example, if a louse-infested pig were to scratch itself on a feeder and then a second pig rubbed against this feeder, then the second pig could become infested with the lice the first pig left on the feeder. However, the second pig would have to contact the feeder within a couple of days since the louse cannot survive longer than 2 or 3 days away from a swine host.

Sometimes, lice may be introduced into a herd by new pigs that are brought in for breeding or finishing. Once these new animals make physical contact with other animals in the herd, the lice will begin to spread.

Signs Your Swine Herd may have Lice

The easiest way to tell if a herd may be infected with lice is to know what to look for. Lice can be found on any age pig from those that are still suckling to adults. The most common sign that pigs express when infested with lice is scratching and rubbing themselves excessively. They will often seek out posts or gates to rub against to relieve themselves of the itching caused by the dozens or even hundreds of lice that are piercing their skin. They may even traumatize themselves in an attempt to relieve the itching. The favorite places on a pig for lice to be include the skin folds around the neck and jowls, the base of the ears, the inside of the legs, and the flanks. Thus, these are the most likely areas of skin for the pigs to traumatize.

Identifying Lice

If you suspect that your swine herd has lice, look closely at the pigs that are rubbing/scratching. The lice will be visible on the skin and each adult louse is about 1/16 inch long. The lice are grayish-brown with black edges and will most often be located in the following body areas: folds of skin around the neck, jowl, and flanks, and on the inside of the legs. The nits (eggs) may also be observed attached to individual hairs, especially in the areas mentioned above. The nits are usually found near the base of the hair where it attaches to the skin.

Economic Impact of Lice for the Producer

Lice are irritating to the pigs. To relieve the irritation, the pigs spend time rubbing and scratching. More time spent rubbing and scratching means less time the pig spends eating and possibly less weight gain. In addition, the lice are a stress for the pig which may translate to decreased gain and increased susceptibility to disease. Finally, large infestations in young pigs may result in anemia since the lice may be removing overwhelming amounts of blood in these pigs.

In addition, lice can transmit diseases such as swine pox and Eperythrozoonosis. Swine pox is a disease which causes skin lesions (papules, pustules, scabs). Eperythrozoonosis is a Rickettsial disease caused by Eperythrozoon suis, which causes anemia and icterus (yellow discoloration of mucous membranes, sclera and inner ears). Swine pox is not life-threatening, but Eperythrozoonosis may lead to poor conception rates and even death.

Treating Lice

Once lice has been diagnosed in the herd, it is essential to implement a whole-herd lice eradication program. If the swine are housed at separate sites, and lice are not observed at each site, then treatment at the affected site(s) should be sufficient as long as there is not pig flow between sites. Ask your veterinarian to help you design an eradication program for your herd.

Preventing Lice

The easiest and most economical way to treat pig lice is to prevent its introduction into the swine herd. New breeding stock should be isolated from the rest of the herd for at least 30 days. They should be treated with an antiparisiticide according to label directions.

New finishing stock should be treated the same before introduction into the herd, unless an entire facility is being filled at once. In the latter case, the new group should be treated upon arrival when they are all put into the facility, and then again in 18-21 days.

The above protocols are prophylactic; we are not really sure if the new animals have lice or not. However, it is more economical and less stressful for the herd at large to treat the new arrivals rather than wait until a potential problem becomes a reality.

Finally, All-In-All-Out (AIAO) management rather than continuous flow can help prevent a herd-wide spread of lice. AIAO can help prevent passage of not only lice but of other parasites and diseases from older pigs to younger pigs. A facility must be emptied and filled as a group and the facility must be cleaned and disinfected between groups to follow the AIAO protocol for effectiveness.


Bowman, Dwight D., Georgi’s Parasitology for Veterinarians, 6th ed.. W.B. Saunders Co.: Philadelphia, 1995.

Leman, A.D., B.E. Straw, W.L. Mengeling, S. D’Allaire, D.J. Taylor, eds, Diseases of Swine, 7th ed.. Iowa State University Press: Ames, Iowa, 1992.


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