• Management Practices
• Control

In general, parasite control in the swine industry is one of a battery of factors which must be considered for maximising the potential of the animals while minimising costs. Swine should always be treated on a herd basis. The goals of parasite treatment vary according to the type of operation in consideration. For example, the purebred breeder is likely to be very interested in any development that will enable him to produce better pigs. Parasites are of major concern as the loss of condition they produce interferes with his evaluation of the stock's genetic qualities. Breeders select strenuously for traits like backfat thickness and feed efficiency, both of which are adversely affected by internal parasites. Feed efficiency refers to the number of kilograms gained by an animal for every kilogram of feed eaten. Obviously, if parasites are sharing the feed, the pig gets less feed and gains less weight. In swine feeder operations, feeder pigs are raised from weaning to slaughter weights. Small decreases in feed efficiency, including those caused by parasite infection, make large differences in profits. In breeding operations, a farmer may be interested in parasite control mainly to keep down mortality among his suckling pigs.

Management Practices

Pigs are healthier with no parasite burdens, so should be de-wormed periodically, especially before being moved to clean facilities. Drug treatment is essential, but control must involve other management practices as well. For example, the larvae of the lungworm Metastrongylus damage the pig's lungs within days of infection and are not affected by commonly available drugs. If pigs are maintained so that infection with worm larvae is possible, damage to body organs will occur before the parasites mature and become susceptible to drugs.

Facilities must not be overstocked. Parasites are transmitted rapidly in crowded conditions. Young and older swine should never be mixed after weaning. The older stock may harbour parasites but show few clinical signs; however, young pigs infected by the same parasites can become very ill. Moist, permanent pastures provide a haven for the survival of parasites. Under such conditions, infective eggs and larvae of worm species like the roundworm Ascaris, the thorny-headed worm, and the whipworm may survive for years. Strongyloides may have a free-living reproductive cycle on such favourable pastures and build up such massive numbers of infective larvae that pigs on these lots may be killed. In addition, these conditions favour the proliferation of intermediate hosts, most importantly the earthworm host of lungworm larvae.

Several management practices are important in these circumstances. Pastures should be drained and marshy areas fenced off. If many parasites are present, the area should be abandoned for enough time for most of them to die. Food and clean water should be supplied in raised troughs, preferably set on concrete. Manure provides an ideal environment for the development of eggs, larvae and the dung beetle, intermediate hosts of the thorny-headed worm. Manure removal and composting will help to reduce infection. In addition, adequate nutrition enables swine to better withstand parasite damage.

Some aspects of parasite control are specific to breeding operations. The goal of these measures is to keep growing pigs as free as possible of parasitic infections. The most important damage to nursing piglets occurs from the migrating larvae of the roundworm Ascaris and the threadworm Strongyloides. Piglets become infected with threadworm in colostrum, and with Ascaris by eating the faeces of infected sows. In both cases, the larvae breaking through the pig's lungs within a week after infection can cause death or permanent unthriftiness. Control is difficult. The migrating larvae are not affected by the drugs currently available, so it is important to limit infection. Pregnant sows must be wormed before farrowing and scrubbed down thoroughly, especially around the teats. The farrowing quarters should be washed with lye or steam. Even with these precautions, piglets may become infected. Testing the piglets for worms and treating accordingly are important management practices.

If the preceding measures are followed stringently, weanling pigs may reach 18kg with few worms, entering the growing pens in optimal condition. However, at this age most feeder pigs have a moderate burden of adult roundworms in their intestines. When placed in growing pens or dirt lots most pigs encounter enormous numbers of eggs or larvae of a variety of common swine stomach and gut worms, including Hyostrongylus, Ascaris, the whipworm Trichuris, trichostrongyles, the nodular worm, the thorny-headed worm, and, when on pastures, the lungworm. These will drastically reduce feed efficiency by their various activities, including blood sucking and competing for feed nutrients. The effects of the various species are additive, and damage is proportional to total worm burdens. Drug treatment of feeder pigs is a necessity. In addition to competing for nutrients, the roundworm Ascaris causes fibrotic damage to swine livers as a result of larval migration. The scars, called "milk spots", make these livers unsuitable for human consumption and are therefore condemned at slaughter. The treatment program can be best assessed by occasionally following pigs to slaughter and examining the carcasses for worms, particularly in the gut and air passages.

Control

Drugs used to control swine endoparasites are termed anthelmintics. These drugs may eliminate parasites in a variety of ways, such as by paralysing them and allowing the host to expel them, by halting their ability to metabolise nutrients, thus killing them, and by limiting their ability to reproduce. Different chemicals may act in one or more of these ways. Anthelmintics should have the following characteristics:

• Be effective, exhibiting a high level of toxicity to the parasite, but not to the host, when used under a variety of conditions. Parasites vary greatly in their susceptibility to different drugs.
• Not leave residual, toxic substances in the host animal carcass.
• Have a wide therapeutic index or margin safety; that is, the dose of the drug used should be toxic to the parasite without causing any damage to the host.
• Be easy to administer to be of practical use

Since the beginning of this century, many anthelmintics have been used to eliminate parasites from their hosts. The earliest compounds were relatively ineffective but much progress has been made in recent decades. The discovery of phenothiazine in the late 1930's was the first major breakthrough in the development of anthelmintics. This drug has a wide margin of safety, and when introduced, provided limited control of several important livestock parasites. Piperazine was first employed as anthelmintic in the 1950's. It is still widely used because it has a high therapeutic index and is effective against Ascaris suum.

A revolutionary advance came in the control of internal parasites came in the early 1960's with the introduction of thiabendazole, the first of the benzimidazole class of compounds. This product was extremely successful in the control of a wide range of nematodes. It was effective against the adults and also killed egg and larvae. It was an effective treatment for Hyostronglyus, Trichostrongylus, Trichinella, Oesophagostomum, and Strongyloides infections in swine.

The organophosphorous compounds, including dichlorvos, haloxon, trichlorfon and many others, are partially effective against gastrointestinal nematodes, including Oesophagostomum and Trichuris. These compounds are cholinesterase inhibitors, which may be toxic in both the parasites and the host. (Cholinesterase is a compound that plays an essential role in the function of the nervous system of animals). Used at the correct dosage, they kill the parasites without damage to the host. However, if other organophosphorius compounds are used to treat external parasites, the two used at the same time may be sufficient to harm swine.

Some anthelminitics have a number of deficiencies. Some of these deficiencies are:

• Many anthelmintics have limited spectra of effectiveness and thus several different treatment regimens have to be given if the swine are infected by more than one parasite species, as is usually the case
• Some anthelmintics when administered to swine cause undue stress and can be toxic
• The introduction of ivermectin (IVOMEC®) overcame many of these deficiencies. Both IVOMEC Injection for Pigs and IVOMEC Premix provide a broad spectrum efficacy against roundworms, lungworms and sarcoptic mange mite and lice.

Field studies have demonstrated a wide margin of safety. Pregnant and breeding pigs may be safely treated provided normal care is taken in handling.

As mentioned above the product is available in two convenient formulations - a low dose injection and an in feed mix.

Both IVOMEC Injection for Pigs and IVOMEC Premix are registered worldwide as a reliable and essential component of any mange eradication strategy.