Agriculture Reference
In-Depth Information
approach is that reliance on dewormer intervention for
control can be reduced, thus conserving the activity of such
dewormers for when they are needed.
Vaccines for other worms that do not feed on blood have
focused on using antigens found in worm secretory and
excretory products. These antigens do have contact with
the host and should stimulate continuous antibody produc-
tion. However, protection has been quite variable, and
marketing such products has been a problem (Smith,
2008 ).
N
EMATODE
- T
RAPPING
F
UNGI
The concept of using microfungi as a biological control
agent against worms is not new (Larsen et al., 1997). These
fungi occur ubiquitously in the soil throughout the world
where they feed on a variety of saprophytic soil nema-
todes. These fungi produce sticky, loop traps on their
growing hyphae, which capture and kill such nematodes.
The best method of using these fungi is to concentrate their
spores in feces to capture developing parasitic larvae. Of
the various fungi tested, only
Duddingtonia fl agrans
spores
have been shown to have a high rate of survival during
passage through the gastrointestinal tract of ruminants
(Larsen et al., 1992). Spores deposited in the feces germi-
nate and trap the developing larvae; thus, there are no or
minimal numbers of infective larvae to migrate out of the
fecal mass, which reduces pasture infectivity. This tech-
nology has been successfully applied under fi eld condi-
tions and is an environmentally safe biological approach
for control of the fecal dwelling free-living stages of
worms in small ruminants under sustainable, forage-based
feeding systems (Fontenot et al., 2003).
Integrated Approaches
Traditional control of worms has relied on grazing man-
agement and treatment with dewormers. Grazing manage-
ment schemes are often impractical due to the expense and
the hardiness of infective larvae on pasture. Currently in
the U.S., the two dewormers approved for goats are fen-
bendazole (Safeguard/Panacur, oral drench) and morantel
tartrate (Rumatel, feed additive). Use of other dewormers
or other methods of administration are not approved and
constitute extra-label use. The evolution of dewormer
resistance in worm populations has led to development of
alternative strategies that could constitute major compo-
nents in sustainable worm control programs. The most
promising of these methods that are immediately appli-
cable are smart drenching, COWP, SL, and FAMACHA.
An integrated approach using various methods should
have an immediate impact on productivity and profi tability
of goat production systems in the Southeast U.S. and other
regions where
H. contortus
and/or other worms can be a
problem. Producers will be able to reduce overall dewormer
usage by using smart drenching procedures and integrating
an alternative (COWP and/or SL) with identifi cation of
animals in need of treatment (FAMACHA), thereby reduc-
ing cost of production while maintaining animal health and
productivity. This integrated approach is essential to
provide future environmentally sound worm prevention
and control technologies to secure a sustainable, growing
goat industry. Integration of other methodology/technol-
ogy certainly will be instituted when evaluation is com-
plete and ready for use.
Vaccines
Efforts have increased in recent years to develop func-
tional vaccines. This has been made possible by newer
technologies in gene discovery and antigen identifi cation,
characterization, and production. Successful vaccines have
been developed for lungworms in cattle and tapeworms in
sheep (Bain and Urquhart, 1988; Lightowlers, 2006). The
most promising vaccine antigen for
H. contortus
was
derived from the gut of the worm, and when administered
to the animal, antibodies are made. When the worm ingests
blood during feeding, it also ingests these antibodies. The
antibodies then attack the target gut cells of the worm and
disrupt the worm's ability to process the nutrients neces-
sary to maintain proper growth and maintenance. Thus,
worms die. This vaccine has been tested successfully in
sheep and goats under experimental and fi eld conditions
(Smith et al., 2001; Olcott et al., 2007). The one drawback
to this vaccine is that the antigen is normally “hidden”
from the host, and a number of vaccinations may be
required to maintain antibody levels high enough to combat
infection. Because the current process for antigen extrac-
tion is quite expensive, this will only be practical when
recombinant technology produces an antigen at a lower
cost.
OTHER INTERNAL PARASITES
Tapeworm (
Moniezia
)
Adult tapeworms reside in the small intestine and feed by
absorbing nutrients from digested feed. They cause very
little damage. Tapeworm eggs and segments are passed in
the feces. Eggs are ingested by fi eld mites and develop into
the infective form. Animals grazing summer pasture ingest
these mites along with forage. Many producers are con-
cerned about tapeworms because they can see the moving
white rice grainlike segments in freshly deposited feces.
