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Non-chemical methods to control parasites in livestock
By Dr Abdul Jabbar, Dr
Murtaz-ul-Hasan, Dr Zafar Iqbal & Dr Zia-ud-Din Sandhu
THERE are many different species of nematode parasites that
infect livestock but only few parasite species cause major
problems, notably Haemonchus, Teladorsagia, Trichostrongylus,
Nematodirus and Cooperia spp. The conventional method to
control is with the use of synthetic chemotherapeutic drugs
(anthelmintics).
 Consumers now demand that the agricultural products should
be both “clean” and “green”. The demand for “clean”
livestock products has followed adverse publicity about
impact of agro-chemicals on human health, and the
development of super-resistant human microbial pathogens,
caused by the use of antibiotics in intensive livestock
production systems.
The term ‘green’ refers to low-input operations based on
grazing animals on pasture against feedlot or housed systems
of production. The move back to pasture-based livestock
management is driven by public concerns over hand feeding of
animals and the bovine spongiform encephalopathy (BSE; ‘mad
cow’) disease scare; the emergence of multi-resistant
microbes derived from selection by ‘growth promoters’
commonly used in the intensive poultry industry, and the
entering of chemical residues into the human food chain.
There is a downside to organic/green farming in the
livestock. Difficulties have arisen in adequate control of
pasture-borne infectious diseases, particularly those due to
nematode parasite infections.
Investigations have concluded that nematode parasitism is
the greatest economic constraint of grazing livestock
production, whether in the industrialized or the developing
countries. The most profound effects of parasitism are on
sub-clinical production loss (i.e., not obvious by visual
appraisal), of which farmers or their advisers – are
unlikely to be aware of.
The assessment of animal health issues associated with
organic farming are often based on farmers’ perceptions in
questionnaires or surveys, rather than on detailed
veterinary investigation. As a consequence, new and serious
animal welfare issues might emerge in organic farming that
are caused by distress suffered by animals as a result of
uncontrolled parasite infections.
To counter this, the move to green and organic livestock
production has also been accompanied by an increase in
research aimed at exploring non-chemical approaches to
parasite control.
Genetic resistance is ultimate in parasite control. It is
economical, permanent solution requiring no extra resources
and no additional costs. However, for most species of
ruminant livestock, animals that have evolved to be highly
resistant to parasite infection are not generously endowed
with desirable productivity traits for wool or meat
production.
These innately resistant breeds are found in the tropics,
where the formidable combination of malnutrition,
environmental stress, long-term and often massive larval
challenge and limited relief by way of effective
anthelmintic treatment have imposed the harshest conditions
for selection, resulting in survival of the fittest.
However, attempts are being made to identify those genes
that encode parasite resistance in laboratory animal models.
With the aid of comparative genomic maps, the aim is to
identify the locations of similar genes in ruminants and to
develop transgenic animals in which genes for resistance are
inserted into economically productive breeds. Pakistan has a
galaxy of different breeds of livestock but none of them has
been exploited for their potential of resistance against
nematode parasite. This could be a very good research issue
based on future demands.
To date, vaccines against nematode parasites have had very
limited commercial success. Early forays into this area were
made using attenuated whole parasites and, although these
showed some promise and marketing opportunities (notably the
irradiated larval vaccine of the cattle lungworm,
Dictyocaulus viviparus).
Better nutrition could reduce worm burden in different
livestock species. Due to internal parasite infection there
is increasing endogenous loss of protein and a reduced
efficiency of the animals.
The increase in parasite challenge associated with the
contemporary livestock production systems must come at a
price with regards to animal productivity, particularly at
times of sub-optimal nutrient supply, when the animal has to
prioritize the allocation of scarce nutritional resources.
Strategic feed supplementation, particularly to young and
peri-parturient animals, can have long-term benefits, and
research is now targeted at fine-tuning the ways, means and
timing of doing this that would be practical, profitable
and, if needed, acceptable to the organic standards.
Another important component of green ruminant production
system could be the use of herbal drugs for the treatment of
parasitic diseases. Anthelmintic medication has its origin
in the use of plant preparations.
In general, these were hazardous concoctions with low
anthelmintic efficacy, especially in ruminant species, and
they rapidly disappeared from human and veterinary use with
the discovery of synthetic anthelmintic compounds.
Although a large and diverse range of herbal de-wormers is
used throughout the world, particularly in Asian and African
countries, generally there is a lack of scientific
validation of the purported anthelmintic effects of these
products. In ruminants, the claimed efficacy is often
associated with farmers observing the occasional elimination
of tapeworm segments, which has little bearing on
production, let alone parasite control.
There is considerable and apparently expanding interest
worldwide in traditional health practices in both the
industrialized and developing countries of the world,
including herbal de-wormers. However, for resource-poor
farmers in developing countries, traditional herbal remedies
based on local plants offer an alternative to the expensive
and often inaccessible commercial anthelmintics.
The use of plant/crops containing secondary metabolites (or
nutricines) can also be a good method of parasite control in
“green” system. The crops are either grazed or fed after
preservation, with the main purpose of reducing parasite
infections, and ideally they can be incorporated into crop
rotation schemes. A specific group of plant polyphenols, the
condensed tannins, has attracted attention in recent years.
When animals are grazed on the leguminous crops which are
rich in these compounds exert great effect to reduced GI
nematode.
For example, the administration of quebracho, an extract of
condensed tannins, might reduce nematode burdens of the
small intestine (Trichostrongylus colubriformis), but not
those of the abomasum (Haemonchus contortus; Teladorsagia
circumcincta). The epidemiological importance of reduced
faecal egg counts continues to be investigated. Grazing of
chicory (Cichorium intybus) by infected sheep has shown some
promising results, in particular with regard to reductions
in abomasal worm burdens.
Keeping in view the world’s trend about tannin containing
plants, the authors have also screened various plants
containing condensed tannins and out of these a few showed
very good results.
For decades, various grazing management practices have been
the cornerstone of epidemiologically based parasite control
strategies in the temperate regions of the world. Not only
were they cost efficient and highly effective, particularly
when combined with anthelmintic treatment, but they also
provided the opportunity for dual livestock species parasite
control, such as with sheep/cattle interchange grazing.
These concepts became established in the applied veterinary
parasitology jargon, with the epithet of ‘dose-and-move
strategies’.
Another concept is the biological control. In the simplest
words, biological control is to kill life with life and
biological control of nematode parasites of livestock is
almost exclusively associated with the nematode-destroying
microfungus Duddingtonia flagrans.
The microfungus has three very important attributes: (i) the
ability to survive gut passage of livestock; (ii) the
propensity to grow rapidly in freshly deposited dung; and
(iii) the possession of a voracious nematophagous capacity.
This fungus thus breaks the lifecycle by capturing infective
larval stages before they migrate from dung to pasture,
where they would otherwise be acquired by grazing animals.
Field evaluation of this concept for a range of livestock
species, in a variety of geo-climatic regions, has been
under way for the past decade. At the same time, several
potential stumbling blocks on the path towards product
registration have largely been overcome.
First, it is now possible to produce large quantities of D.
flagrans spore material; second, long-term field trials
using D. flagrans have shown no adverse effects on the
environment; and third, it has been established that the D.
flagrans is ubiquitous and that very close genetic
similarity exists between isolates from all regions of the
world.
The commonly used means of deployment of D. flagrans spore
material is by a feed additive. To achieve optimal results,
the fungal spores need to be continuously shed in the dung
of animals at the same time that contamination of pasture
with parasite eggs occurs.
Thus, daily supplementation of fungal material is
recommended during the predetermined period of time that
biological control is to be effected. Clearly, much greater
opportunities for this innovation would occur if effective
methods of D. flagrans depot delivery were available.
Courtesy:
The DAWN |
Pakissan.com;
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