Agriculture Reference
In-Depth Information
Parasite Preparations
A wide variety of products are available for parasite control. The best product
is one that gives broad-spectrum control, and the best policy is to use parasite
preparations only when really necessary. The products that are based on the
“avermectin” chemical family currently give the broadest control, and these
include a product called Ivomec (Merck, Rahway, New Jersey), which con-
tains ivermectin.
Vaccines and Other Biologicals
Certain immunizing agents are intended solely for disease protection. They
have little if any effect in treating the disease. These agents are proteins that
are called antigens, and they only stimulate the sheep's immune system to
produce protection against a particular disease. It should be well under-
stood that vaccination and immunization are not the same thing, because
administration of the antigen by vaccination results in immunization only if
the sheep's immune system is normal and functioning. Vaccination must be
accomplished well ahead of the period in which disease exposure may occur,
because it usually takes up to a month for maximum immunity to develop.
Very low levels of protection are observed at 2 to 3 weeks after vaccination,
and with a few kinds it can take up to 45 days after the last dose for maximum
protection.
Immunizing agents fall into one of four classes, and all are commonly
called vaccines:
■
Antisera.
Often called serums or antitoxins; derived from the serum
of hyperimmune animals, which are those that have received multiple
doses of vaccine to confer a high specifi c antibody level against the par-
ticular disease
■
Bacterins.
Contain killed bacteria and/or fractions of the bacterial cell
■
Toxoids.
Contain the inactivated toxins produced by bacteria, usually
clostridial organisms such as those that cause tetanus and enterotoxemia
■
Vaccines.
Derived from viral agents
Antisera
When an antiserum is injected, we are only “borrowing” antibodies produced
in another animal to confer temporary, or passive, immunity. The period of
immunity usually lasts from 10 to 21 days. This type of vaccine is used to pro-