Double L Acres' Foal Development Page
FOAL DEVELOPMENT TIME LINE
pictures to enlarge.
With the naked
eye, you can see only the "embryonic vesicle" which houses
the embryo. The vesicle looks like a shimmering, firm,
translucent bubble, less than ¼ inch in diameter. On the
ultrasound screen, you will see it as a black circle in a
sea of grainy gray (your mare's uterus). At this point, the
embryo is no larger than a pinpoint.
The vesicle has
grown to 1 inch in diameter. It's a shimmering, flabby,
translucent bubble with a dark red dot (the embryo) at one
end. A network of threadlike blood vessels emanates from the
¼ inch dot. You can barely make out the beginnings of animal
features: a head, tiny bumps that will become eyes; a fleshy
tail nub; and four little buds that will eventually become
legs. On the ultrasound monitor, you will see the vesicle as
an irregular, guitar-pick shaped black blob in a sea of
grainy gray. Generally, around Day 24 an embryonic heart is
large enough to be seen on the ultrasound screen. To find
it, focus on the "floor" surface of the blob. You will see a
white smudge, about ½ inch in diameter, resting there; this
is the embryo. Within the smudge, a tiny black dot, about
the size of a pinpoint, will be flashing on and off like a
computer's screen's cursor-this is the pea sized embryo's
1/4 inch in diameter; 5/1000 ounce
The vesicle is
now 2 ½ inches in diameter, roughly spherical in shape, and
somewhat collapsed. The ¾ inch embryo within is now
recognizable as a four-legged critter: it has a blobby dome
for a head, eyelids, rudimentary ears, ridges where the
nostrils will be, and functional elbows an stifle joints. An
ultrasound would reveal the vesicle as a roundish black
blob: look for the white smudge of an embryo to be suspended
from the blob's ceiling, rather than resting on its floor.
This shift of position is step one in what researchers call
"the rise and fall of the embryo." It results from filmy
membranes at the top of the vesicle coming together to form
the umbilical cord. As they do so, they shorten, pulling the
olive-sized embryo up to the ceiling like a chandelier.
3/4 inch long, from crown to rump; just under half an ounce
Day 50 to 55 of
The embryo is
now slightly over an inch long, nesting within the confines
of the 3-inch vesicle. You can see tiny ribs under its skin;
its domed head looks like that of a Chihuahua, and has
developed a distinct skull. Little triangles represent its
ears; the hock and fetlock joints have developed. At this
stage, your future foal officially will graduate from embryo
to fetus. On an ultrasound monitor, you'll find the fetus
back on the vesicle's floor, due to a lengthening of the
umbilical cord. Because of its size-now about that of a
pecan-this will be your last opportunity to view the fetus
via ultrasound; in a matter of weeks, it'll be too large for
1 inch in diameter; less than an ounce
The vesicle is
now flabby and shapeless, conforming to the uterine walls;
the fetus is about 2 1/2 inches long. You can see that it
clearly resembles a horse, thanks to the development of tiny
hooves, complete with soles and frogs. Its head is still
tucked, but less so than before. The fetus is hairless, and
about the size of a hamster.
2.5 inches long; 1 ounce
The fetal head
and neck will be untucked, and are being held level with the
spine in the "normal" horse position. Its sex is now viable:
you can see that little lumps have formed for the scrotum,
if it's a male, or the udder, if it's a female. The fetus is
now about the size of a chipmunk.
4 inches long;
7-inch fetus is about the size of a 6-week old kitten. You
can see a bit of hair on its lips; its ears are unfurling
from its head. They're now nearly 1/2 inch long and are
curled forward. The coronary bands look like raised lines
encircling the tops of its tiny 1/4-inch hooves.
7 inches long; 1 pound
than a pound every 10 days, the fetus now is about the size
of a rabbit. Hair graces its chin, muzzle, and eyelids. If
you look closely, you'll see that eyelashes have emerged.
12 inches long;
The fetus has
quadrupled its weight in just 30 days. Mane and tail hairs
have appeared; it's about the size of a Beagle.
19 inches long;
fetus now looks like a foal: fine hair covers its body, and
it now has a swatch of hair on its tail. It's about the size
of a German Shepherd.
27 inches long;
70 to 80 pounds
In the last week
or so, the fetus's lungs have developed to the point that
they can function in the "real world"; its legs have
strengthened to the point that they can support is weight;
and its hair has coarsened, from the fine, silky texture of
fetus hair, to that of a bonafide foal. As far as
development goes, the fetus is "done." You'll get the chance
to meet your mare's foal in a matter of days or weeks.
(Normal equine gestation can range from 320 to 365 days.)
36 inches long;
about 100 pounds
Click on pictures to enlarge
This perfect ball is an
equine embryo, 3.8mm in diameter and just ten days into its
11-month gestation period.
The tiny bright fleck in the middle
is the inner cell mass which will eventually form the fetus
proper. The remaining cells will form the placental
Rather than attaching itself to the
side of the womb, as with humans, the embryo will move up
and down in the uterus, emitting a hormonal signal that
causes tiny contractions and stops the mare coming back into
Other than a slight increase in
blood flow to the uterus, the mare will be experiencing few
he basic body plan, together with
limb buds and the beginnings of a tail, is now formed and
measures 12mm from the crown of its head to its rump.
The tiny heart, already pumping,
has been visible on scans for the past week and the
rudimentary beginnings of other essential organs - stomach,
liver, pancreas, lungs - are evident.
The fuzzy-looking outer sac, part
of the placental membrane, is called the amnion. The foal
will be encased in this slippery, translucent-white membrane
when it is born.
The mare will still show no
external signs of pregnancy and will continue racing as
usual. Mares do not suffer morning sickness - a horse can
regurgitate food, but cannot actually be sick.
Now 69mm from crown to rump, the fetus
is clearly recognizable as a horse.
The skin remains pale and hairless,
and the eyes are still sealed shut, but the internal organs
are developing, muscles are growing, hoof-shaped feet are
forming and the frog - the rubbery pad on the bottom of the
foot which acts as a pump to move blood up the thin length
of the horse's leg and back to the heart - is forming.
The sex of the fetus can now be
determined. Twins are unusual and unwelcome - mares are not
designed to carry two foals to term and vets will usually
perform a 'twin reduction' to avoid losing both.
A red stain has been used to highlight
the developing skeleton, now almost 75mm long.
The darker areas show calcium
deposits where the bones are starting to ossify. The
hardening skeleton system provides a framework for other
body structures and protects the internal organs as they
Although they become less fertile
with age, mares have no menopause and can breed from about
two years old until the day they die, often in their
mid-20s. Miscarriage is now very unlikely.
The fetus now measures about 100mm and
its features are quite distinct, although it remains
hairless and pale in the absence of pigment.
The mare will be experiencing
hormonal changes and increased blood flow to the uterus -
now the size of a melon - but will not yet look pregnant.
Photo compliments of Melissa Shaw
||DAY 340 BIRTH
Mares need minimal assistance and give
birth quickly - usually within about 20 minutes - and lying
The foal is delivered in the
amnion, the shiny white membrane interlaced with a network
of blood vessels, which it breaks as it is born.
The mare will often stay lying
down, with the foal's feet still inside her and the
umbilical cord attached and passing blood to the foal.
Within an hour, the foal will be up
and being licked and nuzzled by its mother.
Written by Jane Fryer, Photographs by Tim Flach