Swine
Management
News
IMMUNITY VS.
RESISTANCE
ISSUE AFFECTS
HOG HEALTH
Dr. Richard Barczewski
Agricultural Agent
University of Delaware
While attending a pesticide
applicators training session recen
tly, I listened to a talk about the dif
ference between immunity and
resistance. These terms are some
times used interchangeably, which
is incorrect, and it’s worth taking a
little time to discuss the difference.
Resistance describes the ability
of an insect to adapt “genetically”
so as not to be affected by a pesti
cide. If an insect is resistant to a
chemical insecticide like Lindane,
for instance, it is because the insect
has the genetic makeup to resist the
negative effects of the compound.
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Resistance can also be used to
describe the genetic lines of inter
nal parasites in swine and other
farm animal species that are not
controlled by certain common
anthelmintics. Resistance refers to
a population of organisms,
whether they are roundworms,
cockroaches, or Colorado potato
beetles.
Immunity, on the other hand,
describes an acquired ability to
fight off a disease organism. Usu
ally, immunity is acquired when an
organism—a pig, a boy, or even a
plant is exposed to a disease
organism.
For example, your pig gets sick.
If its body can fight off the infec
tion, the animal will be immune to
the effects of future exposures to
that organism.
Immunity describes an indivi
dual, not a population. Each indivi
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dual must be exposed to the dis
ease in order to develop an
immunity.
Resistance, however, is some
thing the organism is bom with.
Why is this distinction impor
tant? Drug-resistant organisms
such as internal parasites, insects,
or bacteria pose a special p, viblem
to the livestock industry. Lives
tock producers must take care
when selecting a deworming agent
or antibiotic.
With swine, most resistant bac
teria are discovered when the vet
erinarian cultures an organism and
determines which antibiotics are
effective against the bacteria caus
ing the problem. An antibiotic that
is not resistant to the bacteria is
what is needed. This test saves on
hit-and-miss shotgun treatments,
especially if a disease organism is
causing major problems in the
herd.
Bacteria cultures and sensitivity
screening are done, as a rule, on a
larger scale'more on milk samples
from dairy cows with mastitis than
on pigs. But it is a valuable tool
worth considering in some
situations.
Similarly, resistant internal
parasites should be identified by a
deworming failure. This is deter
mined through fecal egg counts
before and after a parasite treat
ment. Fortunately for the hog
industry, internal parasite control
failures arc less common m swine
than in sheep.
Immunity is also important
since developing an immune
response in a herd can help to
avoid disease outbreaks. For this
reason, depending on where you
live and how you manage your
herd, your local veterinarian may
suggest a vaccination program that
best fits the needs of your
operation.
Obviously you don’t need (or
want) to vaccinate animals for
every disease known to exist. The
economic factors of the cost of
vaccine and administration of that
vaccine, likelihood of a disease
outbreak, and economic implica
tions of the outbreak should be
considered when deciding on
which immune responses to
acquire.
For example, even though a vac
cine exists to protect large-animal
species from rabies, it would be
imprudent to vaccinate a confined
Route 30 West
at the
Centerville Exit.
Lancaster Farming Saturday, February 9,1991-Dl3
herd automatically The chance for
exposure to this disease is minimal
because the housing system would
prevent contact with carrier ani
mals. Also rabies may not be a
problem m your area, m which
case there is no need to vaccinate.
If, however, you are producing
valuable breeding animals m an
outside operation and an epidemic
of rabies breaks out m your area,
you may consider the cost of vacci
nating the herd justifiable.
Resistance and immunity are
important terms to know for peo
ple concerned about the well-being
and general health of their lives
tock. It’s important that you know
how resistance and immunity can
affect your ability to produce
healthy animals and to recognize
the tools.
New antibiotics, anthelmintics,
and vaccines can help you in over
seeing the health of your animals
and your business.
Grape
Seminar
Set
NAZARETH (Northampton
Co.) — The 1991 Southeast Pen
nsylvania Grape Production Semi
nar will be held February 25, 1991
from 9 a.m. to 3:30 p.m. at the
Holiday Inn Conference Center,
Fogelsville.
The program will include
detailed discussions on sprayer
maximization and new sprayer
technology, recent developments
in grape disease management,
insect management, and canopy
management.
Fungicide resistance and failure
will be covered, including new
option to old disease problems. An
open-ended question and answer
session with the panel of speakers
will top off the day.
The panel will include Dr. Don
Daum, professor, ag engineering;
Dr. Carl Haeselcr, professor,
pomology; Dr. James Travis,
associate professor, plant patholo
gy; and Dr. Michael Saunders,
assistant professor, entomology.
Pesticide credits will be
offered. Cost is $2O, which
includes lunch and materials. For
additional information or a
registration form, contact Eric
Vorodi, Lehigh/Northampton
County agent, (215) 391-9840.