A22-Lancaster Farming, Saturday, March 18, 2000
Seminar Evaluates Importance
Of Poultry Immunity
(Continued from Page A 1)
Mashaly noted a special blood
test which measures the H/L
ratio (the ratio of heterophils
and lymphocytes) as a barom
eter of chronic stress.
The H/L ratio is a “reliable
way to measure stress in birds,”
he told more than two dozen
poultry house managers and
agri-industry representatives at
the seminar.
Measuring the H/L ratio is a
“very easy test you can do to
determine if the individual is
under stress,” said Mashaly.
The ratio is used widely for im
munologists to examine stress.
The ratio is higher with
broilers or layers under stress. It
can indicate heat, humidity, am
monia exposure, hormones, and
nonspecific causes of overall
stress.
A normal H/L reading is .3.
When the H/L ratio reaches 1,
“you have a problem,” said
Mashaly.
The word “immune” comes
from the Latin word meaning
“safe.” The immune system,
similar across species, even
humans, makes us “become
safe,” Mashaly said. “It protects
us.”
The system reacts when for
eign substances, called antigens,
invade the body. The system
reacts against “non-self’ sub
stances in the body, not against
itself. If there are reactions
against the self, those are called
“autoimmune” responses.
The substance, or antigen, re
sponsible for the immune re
sponse can be soluble material
such as proteins on the surface
of an invading cell.
Two different kinds of ac*
quired immunity are active and
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passive. With active immunity,
the body has to “do something,”
said Mashaly. With passive im
munity, the body does not have
to do anything to protect itself.
An example of passive immu
nity is something received in
nately, such as maternal
immunity from mother’s milk
for mammals or yolk for poul
try.
Active immunity occurs when
an individual is exposed to for
eign material. Being exposed to
the substances can be natural,
with antigens in the environ
ment around us, and artificially
through vaccination.
With vaccination, either live
or killed virus can be used. Both
can have the same effect.
Passive immunity is only
short-term immunity.
Sources of immunity include
primary or central lymphoid
organs, or glands, which secrete
hormones. In chickens, there are
two major central organs, in
cluding the bursa of Fabricius
(present only in avian species)
and the thymus (present in poul
try and mammalian species).
The bursa produces B
lymphocytes. The bursa devel
ops at four days of incubation
but disappears after a time. The
thymus is responsible for cell
mediated immunity, producing
T-(for thymus)lymphocytes.
The T-cells can migrate to
secondary organs, including the
spleen, lymph nodes, cecal
tonsil, Hardian gland, bone
marrow, the peyeris patches
(along the intestine), and the
pineal gland. Removal of those
organs does not severely impair
the immune response, according
to Mashaly.
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the body to produce organisms
that can “present” the antigens
for processing. Other types of
cells are generated in the process
to rid the body of dangerous an
tigens.
When vaccinating, the body is
exposed to antigens that cause
this immune response, which
can last for a few hours to a few
days. The first time a vaccina
tion takes place, there is a re
sponse. But it’s the important
response later, the secondary or
anamnestic (Greek for “recol
lection*) response, which creates
a rapid rise in antibodies, which
provides stronger and longer re
action.
The T-cells generated serve a
variety of functions. There are
T-helper, T-suppressor, T
cytotoxic, and Natural Killer, or
NK cells. NK cells are involved
in the destruction of tumors in
the body.
Cell-mediated reactions pro
tect against bacterial, virjas, and
virus- infected cells, antfrprotect
against foreign tissue grafting
and tumor cells. Allergic re
sponses are an immune Re
sponse, of sorts.
Mashaly believes that perhaps
the female has a better immune
response, that the environment
plays a key role in determining
that response, and that hor
mones generated because of
stress (ACTH or corticosterone)
can change the H/L ratio. Diet
and nutrition are critical factors
to boost immunity, including
Dr. Magdi M. Mashaly, associate professor of poultry
science at Penn State, left, not only provided an overview
of the workings of the immune system in birds, but pointed
out the importance of measuring stress a barometer for
the prevalence of disease and a tool to use to boost the
immune system. At right is John Schwartz, Lancaster
County extension director.
energy and protein, proper vita
mins (A, C, E, and B) with min
erals, and genetic factors are
especially critical to birds “when
they are under stress,” he said.
“Vitamins are very important
as antioxidants,” he said.
Mashaly pointed to the fol
lowing strategies to use immu
nity to control disease:
• Reduce the level of expo
sure through biosecurity.
• Reduce overall bird stress
(give proper feed, water, and
housing).
• Chemotherapy, or using
chemicals to boost or improve
immunity, can work but are
costly.
• Vaccination. It’s the best as
far as giving protection, he
noted. But it only protects
against a specific disease. The
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eign substance, or antigen, caus
ing the disease.
But Mashaly cautioned that
the use of too many vaccines too
often has raised issues regarding
resistance. Also, the vaccines
also‘‘play a part yet com
pletely undetermined in how
human immunity is affected,
after humans eat poultry. Over
medicating can be no replace
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management of birds.
Also Mashaly believes that
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