Anticoccidials
Introduction
Coccidiosis is an infection of the intestinal tract
caused by a single cell parasite. All livestock species, as well as wild
animals, can be infected and it is especially prevalent when animals or
birds are grouped together in significant numbers. However it can occur in
less intensively managed situations, including outdoor flocks and herds.
Each species of livestock has a species-specific coccidia that causes
infections in that species. Generally, there is not cross-infection between
species.
The disease is characterised by an invasion of the
intestinal wall by the parasite. The parasite then undergoes several stages
of growth and multiplication, during which there is damage to the mucosal
and submucosal tissues. Severe haemorrhage may result and mortality in an
unprotected poultry flock may be extensive.
Although cattle, sheep and pigs can become infected
causing significant depression of performance, it is usually in poultry
species that the parasite can cause the most devastating losses. For this
reason, it is essential in most poultry rearing situations to use an
anticoccidial agent period to prevent illness and control infections.
The production of affordable, quality poultry meat owes
much to the development of effective anticoccidial products used in the
prevention, control and treatment of coccidiosis.
The Development of Anticoccidials
Chemical Agents
The development of the chicken meat industry in the
1950s required the urgent availability of anticoccidial compounds.
Intensive screening activities by several companies soon produced a
range of chemicals that were effective in the control of coccidia.
Unfortunately, they often became ineffective after a relatively short
period of use due to the parasite’s ability to build up resistance
against them.
For this reason the development of new chemical
anticoccidials proceeded apace throughout the 1960s. By carefully
selecting the anticoccidial compounds, it was possible to rear chickens
with only occasional disease outbreaks.
Anticoccidials since 1970
Several chemical compounds have remained to the
present day and continue to provide a key role in the prevention and
control of coccidiosis. A breakthrough came during the 1970s when a new
class of compounds – the ionophores – was discovered and rapidly became
established as the key component of coccidiosis control.
The ionophores are unique in that they permit a small
“leakage” of coccidia to enable the bird to develop a certain level of
immunity. This allows a greater degree of protection against the
parasite and is a much more efficient method of control. Resistance to
ionophores develops very slowly and there is more of a tendency for
increasing levels of tolerance. This means that the chicken producer is
in a position to adjust the anticoccidial medication programme before
there is an acute outbreak of disease.
The Regulatory Process
Since 1970 there has been a European system for
approval of anticoccidials involving scrutiny by European experts in the
Commission and the European Food Safety Authority.
In the past few years all the anticoccidial products
have been completely reviewed by a specialist scientific body under the
European Food Safety Authority. Major new studies were conducted by
pharmaceutical companies to comply with current guidelines; the review
was extremely thorough, focusing mainly on human safety from both
residue and microbiological aspects.
In 2006, MRLs (maximum residue levels) were published
on the molecules that completed the review. In 2008, the Commission
published a report on the future of the anticoccidials which, in
agreement with stakeholders, including producers and practising
veterinarians, recognised that the products are essential for animal
health and welfare.
The authorised products are listed in a Register
published in the European Official Journal. This can be found at:
http://europa.eu.int/comm/food/index_en.htm
Control programmes
The anticoccidials are designed to be administered orally
in strictly controlled amounts generally via animal feed. These amounts are
carefully researched by the manufacturers and closely regulated by the
authorities. There are a few, however, that can be supplied via the animal’s
drinking water system.
In the early stages of a chick’s life, the immune system
is not fully developed. It is not unusual for protection in this early stage
to be provided by a chemical anticoccidial added to the feed followed by a
switch to an ionophore. Such “shuttle programmes”, as they are known,
provide an adequate balance between control of infection and the development
of immunity in the older bird.
In some cases, shuttle programmes may comprise two types
of ionophore, but this is less common. Other specialists propose a “reverse”
shuttle, where the starting anticoccidial is an ionophore followed by a
chemical based product. And some manufacturers provide an anticoccidial
based on a combination of an ionophore with a chemical.
Vaccines to prevent coccidiosis are available and are
used in replacement layers and breeding stock. A vaccine for use in chickens
for meat is also available.
Vaccines are an important tool, but they are not always
the answer. It is important that there is a full range of solutions, so the
best option can be chosen to prevent this disease on a particular farm.
In other livestock species, the disease is more sporadic
and difficult to predict. However, effective anticoccidials are available
and the disease can be kept under control to permit natural immunity to
develop. These anticoccidials may be incorporated into feed, or some are
administered as an oral drench.
Treatments
In the event of a disease outbreak, it is imperative that
water soluble treatments are readily available that can be administered via
the watering system in the case of poultry, for instance, or as a drench in
the case of cattle or sheep.
Conclusion
It would not have been possible to develop the modern
chicken and turkey industries without the discovery and use of
anticoccidials When used in a structured and monitored programme, modern
anticoccidials are extremely effective and enable the animal to achieve
optimum performance by remaining free of the debilitating coccidiosis
disease. No new in-feed anticoccidial has been developed since the 1980s,
which is perhaps a reflection of the level of success that the ionophores
and the remaining few chemicals have brought to the control of the disease.
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Updated May 2010
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