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Deakin University scientists have revealed
some of the secrets behind the pigeon?s rare ability to produce ?milk? to
feed its young.
Deakin PhD student Meagan Gillespie and research
fellow Dr Tamsyn Crowley, along with colleagues from the University?s
Institute for Technology Research and Innovation and CSIRO Livestock
Industries, have studied the genes behind pigeon ?milk? production. They
found that, like mammalian milk, it contains antioxidants and
immune-enhancing proteins important for the growth and development of the
young.
?Producing milk to feed babies is normally the domain of
mammals, including humans. However, the pigeon is one of only three bird
species (the others being flamingos and male emperor penguins) to produce
a milk-like substance to feed their young,? Dr Crowley
explained.
?We looked at the genes involved in the production of
pigeon ?milk? and found that it contains antioxidants and immune-enhancing
factors. This suggests that, like mammalian milk, it plays a key role in
enhancing the immune system of the developing baby.?
Both female
and male pigeons produce a nutrient rich substance in their crop to feed
their young (squabs). This substance has been likened to lactation in
mammals and is referred to as pigeon ?milk?. This ?milk? is essential for
the growth and development of the pigeon squab, and without it they fail
to thrive.
?Bird crops are normally used to store food. However, in
the pigeon the crop changes prior to ?lactation? in response to hormones
and returns to its ?non-lactating? state at the end of the lactation
period, a bit like the mammary gland,? Ms Gillespie
explained.
?During ?lactation?, a curd-like substance is created
from fat-filled cells that line the crop and regurgitated to feed the
squab. This ?milk? contains protein, fats, minerals and antibodies to
provide nutrition to the young.?
While studies have investigated
the nutritional value of pigeon ?milk?, very little is known about what it
is or how it is produced.
?This study has provided an insight into
the process of pigeon ?milk? production by studying the genes expressed in
the ?lactating? crop,? Ms Gillespie said.
?Birds are different to
other animals in that they don?t have sweat glands, but they do have the
ability to accumulate fat in their outer skin cells (keratinocytes) which
act like sweat glands. We found that the evolution of pigeon ?milk?
appears to have developed from the ability of these outer skin cells to
accumulate fat.
?The way pigeon ?milk? is produced is an
interesting example of the evolution of a system with similarities to
mammalian lactation, with pigeon ?milk? fulfilling a similar function to
mammalian milk but produced in a different way.?
The results of the
study will be published this week in BioMed Central?s journal BMC
Genomics.
About pigeon ?milk?
The crop in
most species of birds is normally used as a food storage area. It is
located between the oesophagus and the top of a bird?s stomach where food
is moistened before further breakdown and digestion through the
gastrointestinal tract.
The pigeon is one of only three bird
species (the others being flamingos and male emperor penguins) known to
produce ?milk? to feed their young.
In pigeons the milk starts to
be produced in the crop of the parent birds two days before eggs
hatch.
During ?lactation?, a curd-like substance is created from
fat-filled cells that line the crop and regurgitated to feed the squab.
This ?milk? is made up of protein (around 60 per cent), fat (up to 36 per
cent), a small amount of carbohydrate (up to three per cent), a range of
minerals and antibodies.
Squabs are fed the ?milk? until they are
around 10 days old. Once the young are weaned the ?milk? stops being
produced.
The unique qualities of pigeon milk have been shown in
previous studies.
One study tried replicating pigeon ?milk?
however, for the squabs fed the artificial substance, their growth was
either very poor or they died. This suggests that there is a unique
quality to the pigeon milk that is necessary for squab growth and
development.
In another study, when pigeon ?milk? was fed to
chickens their growth rate improved by 38 per cent. Since this study, it
has been shown that pigeon ?milk? contains certain antibodies, which
provides further evidence that it is not just a nutrient-based
substance.
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