External parasites are a serious problem. External parasites affect production by feeding on blood, skin and hair. They create wounds that cause discomfort, irritation and in extreme cases, disfiguration to the animal. Major pests include hog lice, mange mites, ticks and flies. Mosquitoes and wound-infesting maggots may also cause severe problems.

Hog Lice and Mange Mites

A high percentage of swine brought to slaughter are infested with lice and mange mites. Excessive scratching and rubbing by pigs nearly always indicate an infestation of hog lice or mange mites.

Hog Louse:
The hog louse is the largest of the domestic animal species of lice but may go undetected because its tan coloration and that of the pig may blend. It is a blood-feeder both in the immature and adult life stages. The life cycle from egg to adult averages 24 days, but the reproduction rate increases in the winter and declines with warm weather. Lice are spread by animal contact or infested bedding.
Louse infested swine itch and the resulting scratching cause the skin to become thickened and cracked, resulting in sores. Infested animals are nervous, gain less weight, are less feed-efficient and tend to be more susceptible to diseases than lice-free animals.

Swine Mange Mites:
There are several different species of mange mites that infect a variety of livestock hosts. Each species of mite is host-specific, that is, swine mites (Sarcoptes suis) infect only swine and are unable to survive on other animals. Mange mites burrow in the skin of swine. The burrowing causes intense itching; subsequent scratching, primarily with hind legs, and rubbing, which leads to lesions. The lesions may appear anywhere on the body but usually start around the head, then the hind legs. Mite production increases rapidly under the scab. Infested skin areas become scruffy, inflamed, raw and cracked. Hair bristles become stiff and upright and hair losses occur, giving an infested animal a rough unkept appearance. A light infestation may go unnoticed, particularly if it starts in the ears. A positive mange diagnosis can be made only by examining skin scrapings deep enough to penetrate mite burrows under magnification because the mites are so small.
Mange-infested animals fail to gain properly, are poor feed converters and are more susceptible to diseases. Market hogs may be docked for appearance and reduction in hide value. The mites spread by animal contact.

Flies:
House flies and, to a lesser extent, stable flies, often are found in large numbers at swine facilities. Both fly species have been implicated in transmitting hog cholera and other diseases. Confined swine housing systems sometimes create fly breeding problems when manure drops through slatted floors of the housing and is allowed to accumulate under the housing. If manure is allowed to crust at the surface, house flies will breed in the pit.