Goats
are hardy browsers that survive despite poor nutrition and poor
management. For this reason, goats constitute an important source of
essential proteins in many poor regions. However, gastrointestinal
parasites
are a problem, as they are worldwide.
Goats are
gold on four hooves in many poor parts of Africa, a
major part of the economy. For years, goat farmers have
been told to dose their entire herd even if just one
goat falls ill with gastrointestinal parasites, and then
transfer them to a disease-free pasture - no easy task
for communal farmers. These cash-strapped farmers have
been blamed for creating drug
resistance but now it seems veterinary practices may be
causing the problem. |
These pathogenic agents exert negative influences on goats and
other farm animals in various ways. Animals may succumb as a result
of
heavy parasitic infection, especially in circumstances where
infection is
accompanied by malnutrition and general poor management. Increased
mortality in goat herds also occurs when parasitism is accompanied
by other
diseases and serious stressful conditions.
Gastrointestinal worms (helminths) in goats cause economic and
nutritional hardship in poor farming communities. Intestinal
parasites cause inefficient feed utilization leading to lowered
growth rates in young animals, reduced
weaning weights, low milk production, enhanced susceptibility to
other
diseases, and poor quality products.
Control of gastrointestinal parasites in farm animals
Strategic and/or tactical de-worming are practices often
recommended by
veterinary practitioners. All animals in a flock must be given
recommended therapeutic doses of anthelmintic (agents that destroy
or dispel intestinal worms) remedies when parasitological diagnostic
techniques reveal high parasite burdens. Animals are transferred to
rested worm-free pastures immediately following the deworming
exercise.
But most poor farmers are unable to carry out the prescribed
deworming of
their flocks. Costs of anthelmintic remedies are prohibitive and the
large
amount of drugs needed to treat all the animals is way beyond the
means
available to the small farmer.
Poor farmers are also obliged to utilize the same communal
grazing
facilities all year round and, consequently, they do not have the
opportunity to move dewormed animals to cleaner environments as
recommended.
In most parts of Africa, a huge variety of ethno-botanic remedies
are
utilized against human and animal diseases. Many of these are used
in
the treatment of parasitic diseases in farm animals. Animals that do
not
show clinical signs are never subjected to treatment with
traditional
medicine.
In a recent study undertaken by me in a communal farming region
in the east of Namibia, it was found that many indigenous farmers
are
replacing the use of traditional remedies with the more potent
registered
parasiticidal preparations. It would seem that the use of registered
pharmaceutical products in traditional medicine is on the increase
among
poor livestock farmers in Africa.
Registered anthelmintic drugs are used by poor farmers to treat
only
individual animals showing clinical signs and, to cut down on costs,
treatment is discontinued once clinical signs subside. The immediate
objective of the poor farmer, for whom every individual animal in
the small
flock is important, is to eliminate the symptoms and prevent death.
The traditional approach to disease control, as described above,
has
always been condemned by veterinary practitioners and drug
manufacturers who say the practice causes anathematic resistance.
Professionals insist on the strict adherence to prescribed doses of
anthelmintics or, better still, to the use of a combination of
anti-parasitic agents.
Anthelmintic resistance
On the contrary, recent observations appear to indicate that
strategic
and tactical protocols are in themselves the main cause of
widespread
development of anathematic resistance experienced worldwide. In
southern Africa, the phenomenon is specially pronounced on
commercial farms where strict adherence to recommended
strategic/tactical practices is the norm. To understand the role of
strategic/tactical deworming practices in the development of
anathematic resistance, it is necessary to briefly review levels of
performance of parasiticidal products.
Few anathematic medicines are 100% effective. According to Van
Wyk et
al.(1998) and Van Wyk (2001), even the best anathematic remedies in
current use are less than 100% effective. This shows that when such
drugs
are administered to infected animals, even at strict recommended
dosages,
not all of the parasitic population inhabiting the gut of the
animals is
eliminated. Depending on the drug's degree of efficacy, only a
certain
percentage of the worms harbored are killed. The sub-population of
parasites remaining in animals at the end of treatment is
consequently 100% resistant to the drug that was used. The result is
that, when treated
animals are relocated to parasite free pastures, as recommended for
strategic/tactical deworming treatment, new parasitic colonies
spreading in
the new farm environment will be drug-resistant strains. Obviously
multiple
drug resistance will develop in the new farm environment if the
deworming
exercise involved the use of multiple drugs. Thereafter the drugs
that were used will be incapable of curing animals developing
symptoms of parasitic disease on that farm.
The role of refugia in preventing anathematic resistance
The word refugia is used to denote parasitic populations that
have not
been exposed to a particular drug and hence still contains a large
proportion of susceptible organisms. It would be expected that a big
source of refugia is the environment inhabited by infected animals
before treatment and relocation since this is where the free-living
forms of the worms are.
As previously mentioned, treatment will eliminate the susceptible
population
of parasites harbored by the host animal showing clinical signs and,
although the resistant proportion of the parasitic population still
persists
in the animal, clinical signs subside and the animal, if properly
fed, may
regain normal levels of production.
When the dewormed animal is maintained within the contaminated
farm
environment, as the case in poor regions, new parasite populations
in refugia, rapidly gaining access into the host animal, will
continue to
dilute the resistant sub-population that was selected by treatment
in
the animal body. More over, drug susceptible populations coming from
refugia will have time to establish themselves in the treated host
animal
before the selected resistant groups harbored have recovered from
the
effects of the medicine on their reproductive activity. This ensures
that the spread of a purely resistant progeny of parasites in the
environment does not occur. The absence of refugia in the clean
pasture does not permit the above occurrence. Hence with the level
of protection achievable by use of anthelmintic remedies of limited
efficacy, continuous utilization of a given grazing environment can
proceed for many years ensuring that time is given for new drugs to
be developed before existing ones have become ineffective as a
result of overwhelming anthelmintic resistance.
One might wonder why certain ethno-botanic remedies in use since
time
immemorial still confer good levels of protection while recently
developed potent medicines, utilized mainly on large commercial
farms, lost
efficacy in relatively short durations. The answer seems to lie in
the
important role of refugia in diluting resistant sub-populations of
parasites
that remain in the gut of treated animals. The use of potent
registered
drugs according to traditional approaches to worm control in poor
regions,
whereby only clinically affected animals are treated and left in the
same
environment with the rest of the herd, appears an affordable and
more useful innovative practice by the small farmer than is the
strict treat-and-move approach.
This not only enables the communal farmer to suppress clinical
disease
in severely affected individual animals and prolong their lives and,
hence,
their usefulness to the household, but it also permits the role of
refugia
in preventing rapid anthelmintic resistance on communal farms.
How do farmers identify heavily infected animals before the
disease gets out of hand? In most instances, clinical signs caused
by gastrointestinal
parasites are non-specific and not easily distinguishable by
unsuspecting
farmers.
FAMACHA © eye colour chart: an easy to handle diagnostic tool
Current diagnostic protocols undertaken by veterinarians for
parasites
are highly specialized and demand special skills and laboratory
equipment.
The FAMACHA © system, initially developed in South Africa for sheep,
has now been shown to work for goats as well and promises an easy
method for diagnosis of heavy parasitic infection by local farmers.
FAMACHA © involves a comparison of the colour of the ocular mucous
membrane of the animal to a colour chart that categorizes animals
into one of five colour categories ranging from 1 (healthy) to 5
(severely anaemic). The degree of anaemia in the animal reflects the
degree of infection by dangerous blood sucking worms, hence the need
for drenching.
Using the FAMACHA © eye colour chart, any farmer, even illiterate
individuals, can assess the eye colour of individual goats and
decide on
which animals to treat. The use of FAMACHA © techniques and
employment
of available potent anthelmintic remedies by poor farmers to treated
animal identified with heavy infection appear sustainable and
effective approaches to combat worm infection and maintain
acceptable levels of goat production in poor farming regions.
More Information:
Dr Kumba is with the Department of Animal Science, Faculty of
Agriculture and Natural Resources, University of Namibia. Private
Bag 13301, Windhoek, Namibia. Tel. 264 61 206 4128/3890; Fax. 264 61
206 3013. E-mail:
fkumba@unam.na
References Used:
Barton, N.J. 1983. Development of anthelmintic resistance in
nematodes
from sheep in Australia subjected to different treatment
frequencies.
International Journal of Parasitology, 13:125-130.
Radostits, O.M., Blood, D.C. & Gay, C.C. 1994. Diseases caused by
helminth parasites. In: O.M. Radostits, D.C. Blood & C.C. Gay
(Eds.), Veterinary Medicine: a textbook of diseases of cattle,
sheep, pigs, goats and horses, 8th ed., Balliere Tindall, London,
1223-1230.
Van Wyk, J.A. 2001. Refugia - overlooked as perhaps the most
potent
factor concerning the development of anthelmintic resistance.
Onderstepoort Journal of Veterinary Research, 68:55-67.
Van Wyk, J.A., Bath, G.F. & Malan, F.S. 1998. The need for
alternative
methods to control nematode parasites of ruminant livestock in South
Africa. World Animal Review: the FAO Journal on Animal Health,
Production and Products, 30-33.
Van Wyk, J.A., Stenson, M.O.S., Van der Merwe, J.S., Vorster,
R.J. &
Viljoen, P.G. 1999. Anthelmintic resistance in South Africa: surveys
indicate an extremely serious situation in sheep and goat farming.
Onderstepoort Journal of Veterinary Research, 66:273-284.
Vatta, A.F., Letty, B.A., Van der Linde, M.J., Van Wijk, E.F.,
Hansen,
J.W. & Krecek, R.C. 2001. Testing for clinical anaemia caused by
Haemonchus spp. in goats farmed under resource-poor conditions
in South Africa using an eye colour chart developed for sheep.
Veterinary Parasitology, 99:1-14.
Vatta, A.F., Krecek, R.C., Letty, B.A., Van der Linde, M.J.,
Grimbeek,
R.J., De Villiers, J.F., Motswatswe, P.W., Molebiemang, G.S.,
Boshoff, H.M. & Hansen, J.W. 2002. Incidence of Haemonchus
spp. and effect on
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