Biology Reference
In-Depth Information
in dosage but is time and labor intensive, which adds to the overall cost of
treatment. Injectable anthelmintics have a significantly longer with-
drawal period in comparison with in-feed formulations 54 and are usually
conserved for the treatment of the breeding stock. The overall cost of
anthelmintic treatment will vary, depending on the choice of anthel-
mintic, number of treatments, and weight of the animals being treated. In
general, for the choice of anthelmintic, pig farmers will base themselves
on information received from their veterinarians or feed companies and,
more importantly, on their previous experiences with a selected
anthelmintic. 21
To date, no studies have reported anthelmintic resistance in A. suum in
pigs. Whether anthelmintic resistance would be easily induced in A. suum
is unknown. However, the development of anthelmintic resistance in
Oesophagostomum spp. and in the closely related horse parasite Parascaris
equorum 59 e 62 suggests that continued malpractice in this area might
eventually lead to anthelmintic resistance in A. suum .
Treatment Regime
Epizootiological knowledge on helminthic infections like ascariasis
on pig farms is still rather limited and this will have definitely had its
impact on the evolution of integrated parasite control programs.
Routine anthelmintic treatments are commonly used these days in
intensive pig rearing systems. Unfortunately, such treatments are not
systematic and treatment schemes vary according to farm and animal
category. Today, the breeding stock is usually treated at 3 e 4-month
intervals or prior to farrowing. Piglets are typically treated upon
entering the fattening units and maybe once more halfway through the
fattening period. However, these treatment schemes seem to be unable
to significantly decrease the infection intensity on a farm. Treatment
frequency must be based on the prepatent period of the worm species.
For Ascaris this is 42 days or 6 weeks. However, when anthelmintic
treatment is ineffective in killing the migrating larval stages, it is
possible that egg shedding occurs earlier as larvae remain in the lung up
to 10 days post-infection. 11 Treatment of pigs every 5 weeks would
therefore eradicate the worms before they are able to produce millions
of eggs and contaminate the environment again. When a strict de-
worming scheme is applied, the infectivity of the environment will
drop, as new hosts will take up eggs from the environment and eggs will
be swept away by cleaning actions or eventually lose their viability. This
will ultimately result in a stock of pigs with a reduced or absent parasitic
burden. It is important to understand that persistence in the repeated
application of
the anthelmintic is necessary.
If
the environmental
Search WWH ::




Custom Search