This
is a disease that is still being researched, and
there are many questions still unanswered. I do
not believe that with a normal diet this is a
problem with European Starlings; however, the
message board receives numerous questions about
it, so I thought this page would be of benefit.
Wild European Starlings normally have an iron
content in their organs 2-10 times higher than
in chickens or quails, especially in the liver
(1310-3300 pg Fe/g wet) and feathers (380_78O~g/g
wet). The iron concentration per body weight ranged
from I53 to I85 ppm, which was 24 times higher
than the values for other birds or mammals. (Garcia,
Planas 1984) I believe this normal high iron concentration
is one of the reasons that European Starlings
are often said to be susceptible to hemochromatosis.
Iron
is a necessary component of the diet and is found
in every cell in the body. It is involved in a
wide range of processes including cell respiration,
DNA synthesis, and is a part of many enzymes.
It serves as a cofactor to the enzymes needed
for the electron transport chain, from which ATP
is generated. Iron in the body is predominantly
found bound to the proteins hemoglovin and myoglovin,
which serve to carry and release oxygen." (Crissey,
Trusk 1993).
"In
captive starlings the absorption of 59Fe was measured
by whole-body counter after varying degrees of
liver iron loading (by i.m. injections of iron
dextran). The haemosiderosis, which occurred particularly
in the post-moult period, had no detrimentral
effect on liver functions. Birds with haemosiderosis
absorbed up to 10% of an orally administered test
dose of the radioactive iron, even when the hepatic
iron concentrations were markedly increased. It
was concluded that the absorption of iron at the
intestinal mucosa in avian species is not as tightly
regulated as that in some mammals." ( Ward,
Smith, Henderson, Peters 1991).
Any animal or human can get the disease. In birds
it is a disease of primarily fruit eating birds,
(frugivorus) such as Mynahs, Toucans, and Lories.
In a laboratory you can induce it by massively
overdosing an animal with iron, as the body can
not expel the overload of induced iron quickly
enough. This is true of anything, for you can
also cause toxicity with massive overloads of
water as well. In a healthy animal the body excretes
the excess iron, but for some reason with Hemochromatosis
the body no longer excretes the iron but starts
to store it in the liver. It can cause the accumulation
of fluids in the body with difficulty breathing,
and it can involve the heart and other organs.
If accumulated in large concentrations, iron is
toxic to liver cells. Toxicity can lead to cell
death and fibrosis.
Iron storage is not usually caused by dietary
iron, but some years ago the theory was that perhaps
the iron in the diets of some captive birds was
causing the overload of iron, and some genetic
factor was the reason for it. Hemochromatosis
is not known to be in wild populations of birds;
it is considered to be a disease of captive birds,
yet in the wild, a mynah's main diet is figs,
which have a very high iron content; if this were
a genetic problem, then you would expect to see
it in wild populations.
Dietary components that increase the storage of
iron include Vitamin C, ascorbic acid (citrus
fruit) and sugar. Other things such as copper
and tannin compete with, or bind up iron so that
it isn't as available. The figs I mentioned are
also very high in tannin. I believe that it will
be shown that the tannin in the native fruit and
water of susceptible birds is one of the main
reasons it isn't seen in the wild. In an article
on tannin found in Green Tea the "Alternative
Medicine Review" - Volume 5, Number 4, August
2000 states that "green tea polyphenols stimulate
the activity of hepatic detoxification enzymes,
thereby promoting detoxification of xenobiotic
compounds, and are also capable of chelating metal
ions, such as iron, that can generate radical
oxygen species." To read the full article go to
Green
Tea. Additionally, Zhi Zhong, PhD, from the
University of North Carolina at Chapel Hill, and
colleagues looked at whether the powerful, free-radical
scavenging antioxidants in green tea could alleviate
some of the problems associated with fatty livers.
They found that "Green tea extract scavenges harmful
free radicals in fatty livers and therefore could
be an effective treatment to prevent failure of
liver transplants."
In a study at Brookfield Zoo, fifty eight European
Starlings were studied after feeding one group
a low iron diet of 148 ppm and the other group
a high iron diet of 3,035 ppm of iron. All birds
were euthanized after four months and tested for
iron storage. Birds in both groups had similar
liver iron content, but the birds on the high
iron diet had significantly higher values. Yet
with this massive overdosing of iron, none of
the birds had developed Hemochromatosis.
Riverbanks Zoo did a similar study with fifty
European Starlings. They were fed a normal dog
food diet for six months to one year; half of
them were also given tannin in their water. They
were tested for iron storage, and no difference
was found between the two groups. The iron was
increased to 800 ppm and the birds were tested
again; the birds given the tannin had lower amounts
of iron in the liver than the birds without tannin.
Again, 800 ppm is an excessive amount of iron
and not representative of a normal diet. No European
Starling in these studies developed Hemocromatosis.
Thomas Roudybush writes: "Recent biochemical evidence
indicates that immunologic stress raises the level
of iron-binding proteins that function in iron
transport and that synthesis of these proteins
is regulated by stress hormones. With our present
level of understanding of iron-storage disease,
it appears that nutrition is, at best, a minor
player in the disease. Stress factors, as mediators
of iron metabolism, need further investigation".
(Roudybush,1999)
No one knew
up until recently what exactly regulated the control of iron in the body.
A few years ago hepicin was discovered. It is believed to be the protein
regulator of iron accumulation.
Hepicin is
located in the liver, and when its levels are
high it blocks the delivery of iron to the cells
and blood, and the excess iron is excreted. Not
only does hepcidin appear as a key regulator of
body iron content, but it may play an important
role in defense against infection by depriving
microorganisms of a ready source of iron.
I
believe that the ability of tannin to chelate
iron has caused us to overlook the fact that tannin
also protects the liver because of its Anti-Oxidation
and Anti-Microbacterial activity. Theoretically,
in birds, tannin could increase or protect the
naturally occurring hepcidin in the body, as several
studies have reported an increase in protein flow
when moderate doses of tannins were used. Current
research has shown that after administration of
lipopolysaccharide (LPS), an iron chelator, that
hepicin increased, thereby blocking the iron not
only in the liver but also in the intestines.
Even though this hasn't yet been researched in
birds, I believe that the iron chelator tannin
could very well have this same effect.
NOTE: Tannin's effect on iron storage was recently
researched at Texas A & M University and it was
found that the addition of inositol or tannic
acid may be a reasonable alternative to low iron
diets. It was also found that tea didn't reduce
the iron levals in the liver of birds with already
high levals of iron, but that tannin helped in
preventing the absorption of iron. (D.Phalen)
We
know that in the wild toucans and mynahs receive
tannin in their diet and drinking water, and this
is the substance that is most lacking in the captive
diet. We also know that hemochromatosis is not
a disease of wild birds. In one antidotal experiment
mynahs were given free choice a bowl of tannin
water and a bowl of plain water each day; the
mynahs seemed to self regulate the amount of tannin
water they consumed. Research has shown that starlings
can not only taste tannin but can also judge its
strength. (Espaillt, Mason 1990)
As there
are many links to hepcidin on Google I won't list any here.
The ppm
of iron found in different dog food types and
brands:
Purina - adult dry dog chow 269, puppy 287
Purina
Moist N Meaty - chicken 365, beef 471
Science Diet dry - adult 184, puppy 338
Poultry mash (approx.) 240 ppm
My thanks
to Martin Vince for his kindness in sharing information on the Riverbanks
project. |
Literature
Cited:
D Phalen, Falcon, Dierenfield, Russell, Olsen,
From a yet unpublished, but accepted for publication,
research paper "Impact of Supplements on
Iron Absorption from Diets Containing High and
Low Iron Concentrations in the European Starling
(Sturnus vulgaris)"
J.E.
Espaillat and J R Mason,1990, Differences in taste
preference between Red-Winged Blackbirds and European
Starlings. Wilson Bull,102 (2) pp 292-299
F.
Garcia, J. Ramis and J. Planas, 1984, Biochem.
Physiol. Vol. VA, No. 4, pp. 651-654,
Ward,
R. J. Smith, T. Henderson, G. M. Peters, T. J.,
1991, Avian Pathology, Vol. 20, No. 2, pp. 225-232
S.D. Crissey,
A. M. Trush, S Black, P. McGill 1993, Effect of dietary iron on the accumulation
of iron in the liver of European Starlings. Proceedings American Association
of Zoo Veterinarians
Thomas E.
Roudybush, 1999, Psittacine Nutrition. Veterinary Clinics of North America:
Exotic Animal Practice Vol. 2 Number 1.
Park, C.H.,
Valore, E.V., Waring, A.J., & Ganz, T. (2001). Hepcidin: a urinary
antimicrobial peptide synthesized in the liver. J. Biol. Chem. 276, 78067810
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