Agriculture Reference
In-Depth Information
become immune by
vaccination
with an antigen that is
killed or modifi ed and cannot cause clinical disease.
Disease resistance is a combination of physical barriers
(skin or mucous membranes), cell mediated immunity
(lymphocytes and macrophages), and humoral immunity
(antibodies).
The objective of vaccination is to activate one or more
of these defense mechanisms in a way that facilitates the
host's resistance to the pathogen or to its toxins. This is
achieved by modifying the disease-causing organism (or
its products like toxins) so that they cause little or no harm
to the animal while stimulating suffi cient immunity to
prevent subsequent infection. The more common ways of
modifying organisms include killing them (killed vac-
cines), inactivating their toxins (toxoid vaccines), weaken-
ing them (modifi ed live vaccines), or extracting specifi c
parts that cause immunity (subunit vaccines). Each has its
advantages and disadvantages. Killed vaccines are very
safe but often of short duration and dose-dependent; live
vaccines are usually long-lasting but have the potential to
be unsafe and are more delicate and require careful
handling, while subunit vaccines are safe but may be
expensive.
The system of immunization is further complicated by
the existence of different strains of organisms, and a
vaccine suitable for one may not protect fully or at all
against another strain. In addition, some vaccines have a
single disease-causing antigen (univalent vaccines) while
others cover several disease-causing antigens (multivalent
vaccines). Cross-protection between organisms or strains
present in a vaccine may also occur.
The degree of immunity produced by vaccination is
affected by many factors, including nutrition status,
age, breed, production, and the presence of other diseases
(like parasites). No vaccine confers complete protection,
and none will protect all animals equally. Immunity
is a powerful weapon against many diseases, and vaccina-
tion should be a part of any herd health program.
However, the choice of vaccines will vary with the circum-
stances on a farm. Vaccination must not be confused
with treatment. The latter applies to drugs of various
types used against disease-causing organisms. Examples
are antibiotics for bacterial infections, anthelmintics
(dewormers), and sprays or dips used against external
parasites.
In the U.S., there are very few drugs that are approved
and labeled for use in goats. It should be noted that the use
of any other drug for a goat in the U.S. is either Extra-
Label or Illegal. Only veterinarians are allowed to use or
prescribe drugs in an Extra-Label manner. Veterinarians
are not allowed to prescribe Extra-Label Use Drugs
(ELUD) unless a valid Veterinarian - Client - Patient
Relationship (VCPR) has been established. Every country
has its own veterinary drug use laws that must be
followed.
Remember to use drugs only under supervision of a
veterinarian or as specifi ed on the label, and do not use
them after the expiration date. Laypersons should consult
with a knowledgeable local veterinarian for advice on the
best products to have on hand in a given environment.
Always observe mandatory withdrawal periods for milk or
meat to ensure the safety of these products after animals
have been treated. Goat meat and goat milk eventually end
up in the human food chain. Failing to follow drug with-
drawal times can cause drug residues to occur, which can
cause serious detrimental effects in the humans that
consume the product (see Appendix C).
Antibacterials
The purpose of antibacterials is to treat or prevent bacterial
infections. Antibacterials must be given at the correct dose
via the correct route for the correct period of time to be
effective. Failure to give the correct dose for the correct
duration can result in disease relapse and in bacterial resis-
tance to the drug.
Tetracycline and penicillin are the most commonly used
antibiotics due to their low cost and spectrum of activity.
Note that neither of these is approved for use on goats in
the U.S. without a veterinarian's prescription. In the U.S.,
Ceftiofur is the only approved for use parenteral antibacte-
rial, and it is available only by prescription.
Anthelmintics (Dewormers)
There are three different classes of anthelmintic drugs
available in the U.S., each with their advantages, uses, and
problems. Availability varies between countries because of
registration requirements. For more information, refer to
the Goat Parasites section of this chapter.
Ectoparasiticides
Insecticides are used for the treatment of insects such
as lice, fl ies, gnats, etc.; and acaracides are used for
the treatment of mites and ticks. Further information
can be found in the Ectoparasite Control section of this
chapter.
IMPORTANT VETERINARY DRUGS
There are several classes of treatments that are often used
on goat farms, and livestock owners and veterinarians need
to know these for routine use or emergencies.
