The objective therefore is to manage the environment to prevent the pig gaining access to faeces after the larva have become infective. It can be seen from Fig.11-5 that in practical terms this is approximately 5-7 days. A routine parasite examination of faeces every six months will establish the status.

Field experiences over many years have shown that if sows are housed in stalls or tethers and they have no access to faeces, internal parasites are almost eliminated, with the exception of the ascarid or large white worm. The infective period for this larva is two to eight weeks and generally the longer period. However the egg will survive outside the pig for long periods of time. Provided good hygiene is practised on the farm and faeces and liver surfaces are monitored, it is not necessary to treat.

The danger areas for the build up of infections are the permanently populated areas such as boar, mating and gilt holding pens. Provided these are cleaned out regularly, herds can be maintained with negligible levels of parasites.

Parasite control in loose-housed sow herds is less predictable but again depends on hygiene, drainage and the regular removal of faeces. Field experiences with the foregoing provisos, also demonstrate it is not usually necessary to treat, but each herd must be assessed individually together with its history. Faeces should be examined every three months.

In finisher herds the adoption of multi-site operations or segregated systems all-in all-out have virtually negated the necessity for treatment.

In outdoor herds however parasite control is difficult. Twice yearly worming and in-between faeces examination gives good control and an insurance against the build up of infections.

Because the exposure to parasites in many commercial systems is low the corresponding immunity levels in the pig are also low. This will mean that within any given herd a number of animals will be highly susceptible and therefore the number of larvae required to produce disease is minimal.

Key Points to the Control of Roundworms

• Assess the husbandry system. Is there access to faeces after four days?
  - In intensive reared indoor pigs on concrete or slats treatment is unlikely to be necessary.
  - If sow stalls or tethers are used - treatment of sows is unlikely to be necessary.
  - If sows are loose-housed - how often are faeces removed?
  - If sows are outdoors - worming is probably necessary.
  - If sows are housed in permanent paddocks worming is essential.
• Are there permanently populated pens on the farm? Could these create reservoirs of infection? For example - gilt pens, boar pens, or grower pens. Check faeces samples.
• Assess the history of the management system. Have parasites been a problem?
• Carry out a faecal screen every six months.
• If there is a loose-housed system with faeces remaining for two weeks or more a faeces screen should be carried out every three months. A worming programme is likely.
• If sows are outdoors use a worming programme every 4-6 months.
• Move outdoor sites regularly every one to two years.
• When pigs are weaned into arcs in the field always move to clean ground.
• Always move farrowing arcs to new ground between farrowings and burn the old bedding.
• Remember worm eggs and larva survive in warm damp wet conditions. Younger animals are more susceptible than older ones. Problems are more likely in summer than winter.
• Use farrowing, first, second and finishing accommodation on an all-in all-out basis. Wash out using a detergent between batches.
• Assess the body condition of sows.
• Examine livers regularly at the slaughter house.
• If parasites are a problem in growing pigs check the pens.
• Permanently populated grower finisher pens will help to perpetuate ascarid infections.
• When outdoor pigs are moved to fresh paddocks always worm the group of animals 14 days before hand.