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Maternal nutritional programming in the sheep : effects on post-natal growth, mammogenesis and lactation in adult-ewe offspring : a thesis submitted for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, Aotearoa New Zealand
Developmental
programming
is
the
concept
that
environmental
factors,
particularly
during
foetal
life,
can
alter
development,
metabolism
and
physiology
of
an
organism
and
this
can
have
consequences
later
in
life.
There
is
growing
interest
in
developmental
programming
in
livestock
species,
particularly
effects
of
maternal
pregnancy
nutrition,
which
is
easy
to
manipulate.
Recent
research,
using
a
sheep
model,
has
shown
that
milk
production
in
ewe
offspring
may
be
susceptible
to
maternal
nutritional
programming,
such
that
over
nutrition
(ad
libitum)
of
the
pregnant
dam,
compared
with
maintenance
nutrition,
may
impair
their
first
lactation
performance
and
result
in
the
weaning
of
lighter
lambs.
The
present
study
however
revealed
that
maternal
nutritional
programming
effects
on
lactation
performance
in
ewe
offspring
did
not
persist
over
their
productive
lifetime.
In
a
new
study,
the
critical
programming
period
was
narrowed
down
to
early
gestation,
coinciding
with
early
mammogenesis
in
the
foetus.
In
this
study
only
twin-‐born
ewes
were
examined
due
to
their
economic
significance
in
commercial
sheep
production
and
due
to
their
increased
susceptibility
to
nutritional
insult
in-‐utero.
It
was
revealed
that,
in
addition
to
over
nutrition
(ad
libitum),
under-‐nutrition
(sub-‐maintenance)
of
the
dam
during
early
pregnancy
also
impaired
first
lactation
performance
of
twin-‐born
ewe
offspring
when
compared
with
maintenance.
Transcriptomics
analysis
using
RNA-‐seq
identified
that
nutritional
programming
affects
late
pregnancy
mammogenesis,
rather
than
secretory
cell
function
during
lactation,
in
ewe
offspring
during
their
first
parity.
Ewes
born
to
ad
libitum-‐fed
dams,
in
particular,
appeared
to
have
impaired
regulation
of
cell
cycle
while
ewes
born
to
sub-‐maintenance-‐fed
dams
had
reduced
expression
of
genes
associated
with
the
extracellular
matrix,
both
of
which
may
influence
cell
proliferation.
As
a
consequence,
both
ewes
born
to
ad
libitum
and
sub-‐maintenance-‐fed
dams
may
have
had
fewer
mammary
secretory
cells,
resulting
in
reduced
lactation
performance.
The
findings
of
this
thesis
indicate
that
differences
in
first-‐lactation
performance
of
ewe
offspring,
as
a
result
of
maternal
nutritional
programming,
may
be
mediated
by
impaired
proliferation
of
secretory
epithelial
cells.
These
findings
contribute
to
our
knowledge
of
the
mechanisms
of
developmental
programming
of
the
mammary
gland
and
presents
a
platform
for
future
investigations
which
may
ultimately
lead
to
the
ability
to
manage
and
manipulate
lactation
performance.
