Broad-Spectrum Control of Worms

By Dr. T. Bonner Stewart, Professor of Parasitology, Louisiana State University. - Worm parasites can kill pigs, but more commonly they simply cause stress. Stress leads to loss of appetite, reduction of daily gain, and poor feed utilisation. The weakened pig can also become more susceptible to bacterial and viral diseases that may be easier to detect than the underlying subtle performance problems generated by the parasites. This article reviews the worm parasites of major importance to pig production throughout the world and answers the question What good is it to remove parasites?
calendar icon 17 May 2001
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Worms in Pigs

Ascaris suum, the large roundworm, is the most common parasite of pigs worldwide. The success of A. suum is due to the great reproductive potential of a single female worm in producing 250,000 or more eggs per day and the longevity of the thick-shelled, sticky egg that can survive for 6 years or more in cracks and crevices of buildings or sheltered areas of lots and pastures.

Oesophagostomum spp., O. dentatum, the common nodular worm, and O. quadrispinulatum, the long-tailed nodular worm are found worldwide and are of greater importance in breeding animals. Unlike most of the worm parasites of pigs, initial infection with nodular worms does not elicit a strong immune response and populations tend to build up in older animals that are re-exposed.

A review of the worm parasites of major importance in pig production throughout the world begins with Strongyloides ransomi, the intestinal threadworm of the suckling pig. This is a particularly important parasite in warmer temperate areas. Strongyloides ransomi can be transmitted from the sow directly to the suckling pigs in the colostrum. Unlike most parasitic worms, strongyloids can reproduce outside the pig. Eggs passed in the faeces can develop into free-living adults within a few days to produce large numbers of infective larvae that are skin penetrators.

Trichuris suis, the whipworm, is an important parasite in many areas of the world, especially in pigs raised outdoors, but also can be a problem in housed pigs. The thick-shelled egg can survive for 6-years in protected areas.

Metastrongylus spp, the lung worms, require earthworms as intermediate hosts and are common in pigs raised outdoors. Earthworms can retain lungworm infective larvae their entire lives.

Hyostrongylus rubidus, the red stomach worm, is more common in pigs on pasture and can be of special concern in sows on pasture. Along with the nodular worms, the red stomach worm is responsible for “thin sow syndrome.”

Physocephalus sexalatus and Ascarops strongylina are thick stomach worms of swine that require the dung beetle as an intermediate host and can be present in swine on pasture. Likewise, Macracanthorhynchus hirudinaceus also require a beetle as an intermediate host. Stephanurus dentatus, the swine kidney worm, is a very important parasite of outdoor pigs in the warmer temperate and tropical areas of the world. Condemnation of livers, kidneys, loins, and even entire carcasses can result from migration of immature worms.

Worm parasites can kill pigs; more commonly, however, they stress pigs. Stress leads to loss of appetite, reduction of daily gain, and poor feed utilisation. The weakened pig can have an increased susceptibility to bacterial and viral diseases that may be easier to detect than the underlying subtle performance problems generated by the parasites.

Internal organs of swine showing predelection sites of worms

Internal organs of swine

Table 1 shows controlled trials carried out with most of the important worms of pigs. It is clear that even low infections have detrimental effects on the performance of growing pigs.

Efficacy of IVOMEC against worms is excellent. Worldwide trials conducted with infected pigs have shown that both the injectable formulation and the in-feed premix formulation have an efficacy of 97% to 100%.

A series of controlled trials was conducted in the United States and Europe; Table 2 shows results for IVOMEC Injection at the rate of 300 µg/kg. Table 3 shows results for IVOMEC Premix given at 100 µg/kg for 7 consecutive days.

In some trials with naturally infected pigs, other parasites were present in low numbers for statistically significant results. IVOMEC had good efficacy against some of the parasites found in small numbers, including the thick stomach worm, P. sexalatus; the short-tail nodular worm, Oesophagostomum brevicaudum; and the thorny-headed worm, M. hirudinaceus.

Table 1.
Effects of worm parasites on the productivity of growing pigs.
Parasite No. of Pigs ADG* (kg) % Diff. F/G* % Diff.
Ascarid 8 .85 -2 3.20 -5
Control 8 .87 3.03
Nodular worm 12 .81 -2 3.04 -6
Control 24 .83 2.86 Whipworm 12 .84 -6 3.30 -3 Control 12 .89 3.21 Threadworm 16 .70 -9 3.03 -6 Control 16 .77 2.86 Kidney worm 10 2.65 -20 3.05 -3 Control 10 .81 2.97 Red stomach worm 6 .59 -21 3.52 -6 Control 6 .75 3.29 Lung worm 12 .79 -26 4.17 -18

Control 12 1.06 3.43 *ADG=daily gain, F/G=feed-to-gain ratio. ADG and F/G values based on 91-day feeding period except for the red stomach worm (based on a 83-day feeding period) and lung worm (based on a 56-day feeding period). Data from Stewart et al, 1985; Stewart & Hale, 1988; Baudena et al, 1997.
It is clear that even low infections [of worms] have detrimental effects on the performance of growing pigs.

Table 2 - Results of Trials with IVOMEC Injection
Parasite Stage No. of
No. of
% Efficacy
Ascaris suum adult 10 178 100.0
L4 4 70 99.5
Oesophagostomum spp adult 5 102 99.0
Metastrongylus spp adult 3 49 100.0
Hyostrongylus rubidus adult 3 62 98.0
L4 1 12 99.0
Strongyloides ransomi adult 1 20 98.5
*Data taken from trials conducted for dose confirmation efficacy are available on request.

Table 3 - Results of trials with IVOMEC Premix.
Parasite Stage No. of
No. of
% Efficacy
Ascaris suum adult 6 118 100.0
L4 1 56 100.0
Oesophagastomum spp adult 4 76 99.0
O. quadrispinulatum adult 1 20 99.0
Hyostrongylus rubidus adult 3 56 100.0
Metastrongylus spp adult 5 94 100.0
Ascarops strongylina adult 5 98 100.0
Stephanurus dentatus adult 1 33 100.0
L4 2 60 100.0
*Data taken from trials conducted for dose confirmation efficacy and from Alva-Valdez et al, 1989.

Efficacy of IVOMEC against worms is excellent. Worldwide trials conducted with infected pigs have shown that both the injectable formulation and the in-feed premix formulation have an efficacy of 97% to 100%.

IVOMEC has substantial effect on reduction of migrating A. suum and efficacy against the 4th and 5th intestinal stages (Stewart, 1995). A significantly lower number of larvae were detected in the lungs of pigs treated with IVOMEC compared to nontreated pigs (Urban et al, 1989). In trials with IVOMEC Premix, the larvicidal effect was borne out. Pigs were infected with A. suum eggs and given IVOMEC Premix for 7 days beginning either on Day 2 or on Day 9. Efficacy was 98.9% and <99% in the two treated groups, respectively (Rehbein et al, 1996).

IVOMEC Premix is >99% to 100% effective against S. ransomi somatic (tissue dwelling) larvae in sows when fed for 7 consecutive days during mid- to late pregnancy (Barth and Preston, 1985). This should prevent transmission of the worms to the piglets when they are being suckled and, in fact, IVOMEC Injection given to sows 10 to 16 days prior to farrowing prevented the discharge of S. ransomi larvae into the colostrum (Barth et al, 1996). Pigs born to sows injected with IVOMEC prior to farrowing weighed 0.78 kg more at 28 days than pigs from untreated sows on the same German farm (Busse et al, 1992). Treating sows with IVOMEC prior to farrowing is an excellent method of preventing transmission of two important parasites of suckling pigs, S. ransomi and Sarcoptes scabiei (the mange mite), that are normally transmitted directly from the nursing sow.

Whipworms (T. suis) are the most difficult intestinal worms to control, and all have poor to variable results. Apparently, T. suis needs to be exposed to a drug over a longer time period than other nematodes for high efficacy. IVOMEC Premix fed to infected pigs reduced egg counts to 0 within 6 days after treatment; the efficacy at 14 days was 97.7%. After treatment, only 0%-14% of eggs developed during the first 5 days and no eggs developed after Day 6 (Arends et al, 1996).

Benefit of Worm Removal

What good is it to remove parasites? Once infected with parasites, will their removal yield enough benefit to justify the expense? If so, when should treatments be given — to the young pig, to the older pig, or both?

In an attempt to answer these questions, two trials with 90 pigs infected with A. suum, Oesophagostomum spp and S. ransomi, were performed. Treatment of smaller pigs resulted in greater feed conversion efficiency (FCE) and a higher carcass dressing percentage. The value for treatment was estimated at $3.32 above the cost. Treatment of larger pigs resulted in even higher daily gain and better FCE, yielding a net profit of $3.83 (Stewart et al, 1991; Stewart et al, 1996). The results point to an important biological fact: a young growing animal's energy intake is directed to the production of bone and muscle. By removing parasites, there is reduced impairment of the process, resulting in a carcass with a high dressing percentage (Garriz et al, 1987). In the older animal, the compensatory gains after worm removal will tend to the deposition of fat as well as muscle. It is clear, however, that young and older pigs benefit from worm removal.

In another trial, 90 pigs treated with IVOMEC achieved greater gains and were more efficient in feed conversion than nontreated controls. The net profit per pig from treatment was $5.30 (Gutierres-Poster et al, 1990).

It has been shown that natural untreated exposure to worms during the growing phase permanently reduces the growth potential. In a dirt lot study with 96 pigs, those treated every 60 days with IVOMEC had a 19% greater gain and were 5% more efficient in feed utilisation than nontreated pigs (Urban et al, 1989).

Decontamination of premises harbouring ascarid eggs is very difficult. Most disinfectants actually improve the chances of egg survival because they are not effective against the embryonated egg but kill the microorganisms that prey on the eggs. Thorough scrubbing of floors, walls and equipment followed by steam that reaches into cracks and crannies comprises one of the most satisfactory ways of sanitising to prevent ascarid transmission from contaminated premises. There is no doubt that ascarids are the most difficult of worms to eliminate from a herd; constant vigilance is necessary to prevent their introduction by cockroaches, mice, rats, birds and contaminated shoes and boots.

Life cycle of Ascaris Suum (Large roundworm)

Ascarid Life Cycle

The eggs of Ascaris Suum are in the one-cell stage as they pass out in the faeces. They develop within the egg to the 3rd stage in about 28 days and require an additional 14 or more days to become infective.*

Eggs ingested by the pig hatch and the ensuing larvae penetrate the wall of the large intestine and enter the circulatory system.

Larvae are in the liver from 18 hours to 4 days after leaving the intestine, then move to the lungs where they can be found for about 4 days.

Beginning on the day 8 to day 10, larvae penetrate the alveoli of the lungs and enter the airways and are swept to the mouth and swallowed. Shortly after reaching the small intestine, larvae molt to the fourth stage from days 9 to 10.

The final molt occurs 25 to 45 days after infection. Egg production by the female begins from 40 to 53 days after infection.**

* Genneen et al 1999
** Douvres et al 1969

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