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Penn State
I Poultiy T\ f
Pointers ;
Agricultural & Biological Engineering Agricultural Hcoitbmics
EGGSHELL
FORMATION
IS A DYNAMIC
AND SENSITIVE
PROCESS
Carol V. Gay, Ph.D.
Avian Physiology
Professor of
Molecular and
Cell Biology
And Poultry Science
Penn State
Fred D. Gay, M.S.
Agricultural Engineering
Penn State Alumnus
(H+) and a carbonate ion (CO,=).
An eggshell consists primarily When the latter structure combines
of calcium carbonate. The manner with a calcium ion (Ca*+), thtf ions
by which calcium arrives at the precipitate out of solution,
eggshell was described in an ear- Crystalline calcium carbonate is
lier article (Lancaster Farming, quite insoluble in water even
May 14, 1994). though it precipitated out of an
To review briefly, calcium & aqueous solution. It is relatively
derived from food, is absorbed by inert chemically because of the
the intestine, and is passed into the plus and minus charges balancing
bloodstream. As blood passes each other electrically in a dynam
through the shell gland, calcium ic equilibrium. About 100 million
leaves the blood, moves into and COj= ions fitted end to end would
through the shell gland tissue, and he an inch long and Ca++ ions are
precipitates onto the surface of the ■ comparable size. The many
egg. Calcium is a positively replications of the CaCO crystal
charged ion and consequently pre- structures interlock with each
cipitates out of solution when it 'Other in a three dimensional lat
interacts with appropriate nega* ticeworic called aragonite to form
lively charged ions, such as the eggshell. The chemical corn
carbonate position and crystal structure of the
Where docs the carbonate ion eggshell is similar to high quality
come from? The short answer is limestone or high purity neat
from carbon dioxide, a metabolic hydrated Portland cement This
waste product derived from the gives a suggestion of how an eggs-
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breakdown of -glucose. Carbon
dioxide is produced by all tissues
and is expelled from the body
mainly through exchange for oxy
gen in the lungs. The shell gland
utilizes carbon dioxide produced
by its own metabolism as well as
by using C0 2 present in the bloods
tream for making an eggshell. The
conversion of CO ( into carbonate
requires combining CO t with
water (H,O). This results in the for
mation of carbonic acid (H a COJ.
Carbonic acid spontaneously
breaks down or dissociates in two
steps to form two hydrogen ions
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hell can be such strong material,
especially when in compression.
Caibonic acid forms whenever
CO, and water are present. Howev
er, in the shell gland the sponta
neous conversion of CO, into car
bonic acid and subsequently into
carbonate ions is not fast enough to
support daily eggshell formation.
This problem is solved by the pre
sence of an enzyme in shell gland,
carbonic anhydrase. which catal
yzes (speeds the process without
itself being consumed) carbonate
formation. This catalytic material
is a protein that is also found in
many body tissues. It assists in the
formation of carbonate-rich fluid
in the chambers in the eye; it helps
foster gas exchange in the lungs
and the kidneys to form urine, to
mention a few of the many roles of
carbonic anhydrase.
When carbonic anhydrase is
inhibited, different tissues are
affected in different ways. Pres
sure build up in eyes during
glaucoma can be relieved by inhi
biting caibonic anhydrase. On the
other hand, caibonic anhydrase
inhibition causes the breathing rate
to increase and causes the kidneys
to form a watery urine. In the shell
gland, inhibition of carbonic
anhydrase causes a marked and
rapid cessation of eggshell forma
tion. Consequently, the hens’ body
must have an elaborate control
mechanism to regulate metabolic
CO, and resultant CO,=so that suf
ficient quantities are available for
timely eggshell formation.
Various chemicals can affect
carbonic anhydrase adversely. A
relevant example is the problem
that fish-eating birds had before
the banning of DDT, which was
relatively stable and therefore per
sistent in the environment. DDT
was washed from the land into
bodies of water where it entered fat
stores in fish. Birds eating fish,
such as ospreys and bald eagles,
received high doses of DDT. Eggs
hell formation and subsequent
development of the offspring was
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payely impaired because of the sweating, but by panting. During
inhibitory effect of DDT on car- bouts of hot weather or other types
borne anhydrase. 0 f hcat strcss panting rates can be
A final pomt concerns the high enough to cause a reduction in
importance of body levels of CO, total body CO to a level that
for good eggshell formation. Birds results in thin-shelled eggs,
maintain body temperature, not by
United Soybean
Board Selects CEO
ST. LOUIS, Mo. John
Becherer has been selected as the
new chief executive officer by the
63-member United Soybean
Board (USB). Becherer serves as
the senior director for develop
ment and programs at the Conser
vation Technology Information
Center (CTIC), West Lafayette,
Ind. He will begin his duties on
October 1.
The all-farmer board selected
Becherer by unanimously
approving a recommendation
from their search and executive
committees at their quarterly
meeting. “John is a consensus
builder who can help unify the
industry,” said USB Chairman
and Fulton, Mich, farmer Barry
Mumby. “John will work to more
closely involve states with USB
activities and programs. We want
to assure state organizations that
there’s a two-way street at USB
and that we look forward to their
participation in USB projects.
John’s history as a consensus
builder will be instrumental in
that effort.”
Becherer views his new posi
tion as an opportunity to continue
his career-long crusade to help
Youth Production Class
Set For Barrows
HARRISBURG
(DAUPHIN CO.)
The Keystone Interna
1-800-447-7436
Unctttw Fanning, Saturday, October 1, 1994-C3
farmers farm more profitably. “1
want to help make soybeans as
profitable as they can be,” said
Becherer. “I look forward to
working with an organization that
promotes the profitability of agri
culture producers.”
Prior to working for CTIC,
Becherer worked as a consultant
for Demeter Inc., the nation’s
10th largest grain merchandising
firm. The position helped Becher
er develop an international view
of the challenges that face soy
bean growers. “We don’t live in a
microcosm. We’re in a global
economy,” said Becherer. “To
make soybeans profitable, we
must continue to research for new
uses of soybeans and expand
export markets.”
Becherer looks forward to a
smooth transition into the CEO
slot at USB. “I don’t anticipate
any rapid change,” he said. “USB
is in a situation where they’re
moving forward in a positive and
appropriate manner. I think soy
bean farmers will recognize USB
as an organization that truly
meets the needs of the farming
community. I invite input from all
soybean farmers in that regard.”
Winola only, call
140042 HM
tional Livestock Expo
sition will be held Octo
ber 6-10 here at the
Farm Show Complex,
Exhibitors from
Pennsylvania can enter
one or two pigs in a
barrows class, plus
other animals that
would be entered in the
regular junior barrow
show.
In June the pigs
were weighed and
identified at the farm.
Now they have been
brought to the exposi
tion for final evalua
tion.
Pigs will'be judged
on-foot, but they will
also be judged on the
basis of weight gain
and carcass merit. This
will reward junior
exhibitors not only for
good genetics, but
sound swine manage
ment as well.
To date, approxi
mately 43 animals have
been entered in this
class, representing
about 28 Pennsylvania
youth. All pigs
weighed in June had to
be less than SO pounds.
Premiums in this
class are $5OO for the
champion and $250 for
the reserve. The prima
ry purpose of this class
is to tell how much
muscle an animal puts
on each day, thus giv
ing breeders more
information on feed
conversions and feed
efficiencies.