Agriculture Reference
In-Depth Information
was briefl y described with the uterus. This type of placenta
is called “cotyledonary or multiplex placenta.”
As a whole, the placenta has three membranes: the
chorion, the allantois, and the amnion. The chorion is the
most external membrane of the placenta, in contact with
the maternal uterus. The allantois joins the chorion and
contributes to the so-called chorio-allantoic placenta. The
amnion is the most internal membrane, which surrounds
the fetus and allows it to accommodate movements of the
head, body and limbs in the amniotic fl uid.
The umbilical cord extends between the embryonic
umbilicus and the placenta, and makes the connection
between the embryo/fetus and the placenta. A gelatinous
substance in which one vein carrying oxygenated maternal
blood and two arteries returning the venous blood (all of
them called umbilical) are embedded, forms the umbilical
cord.
The Glandular Tissue
The glandular tissue, whose function is to produce milk,
is separated in lobes by connective tissue septa. Each lobe
is divided in lobules, clusters of up to 200 alveoli that
secrete into a central ductule (the lactiferous alveolar
ductule). The lobules are separated from each other by a
thin layer of connective tissue.
The Duct System
The duct system starts with the alveolar ductules, which
continue with intralobular and interlobular ductules. All
ductules are located within a lobe. From the end of each
lobe, the lactiferous ducts convey milk to the lactiferous
sinus. The lactiferous ducts are visible without magnifi ca-
tion, and they become larger and larger as they approach
the lactiferous sinus. There are 6-9 large lactiferous
ducts according to Nickel et al. (1981), and 12-15 accord-
ing to Barone (1978). They are located caudolateral (right
and left) to the glandular tissue (which is perforated by
small - and medium - sized ducts).
The lactiferous sinus, or cistern, is the dilated distal part
of the duct system formed by the confl uence of the lactifer-
ous ducts, and consists of two parts. The glandular part, or
gland cistern, is located in the ventral end of the mammary
gland, whereas the papillary part, papillary or teat cistern,
is located within the papilla (the teat). In full lactation, the
teat cistern is up to 7 cm long and 2.5 cm wide. The papil-
lary cistern continues in the tip of the papilla, connecting
the papillary part of the lactiferous sinus with the outside
by the papillary orifi ce or ostium. The papillary duct, also
called teat or streak canal, is conically shaped and has a
sphincter (Figure 6.36b). The rosette of Fürstenberg can
be noticed at the junction of the papillary cistern and the
papillary canal (Pugh, 2002) and consists of mucosal folds.
In older goats, the lactiferous sinus extends under the
skin and can be palpated. There is a small accessory teat
0.5-1 cm long at the base of each mammary gland.
Occasionally, caudal to the main teats, supernumerary
teats can be observed. Also, abnormal teats may be found,
such as double teats, forked teats, etc. Rudimentary devel-
oped and even functional mammary glands also exist in
some male individuals, in front of the scrotum.
The blood supply to the udder is very important for
assessing the milk production. It is provided by the exter-
nal pudendal artery and by the mammary veins. The exter-
nal pudendal artery branches in the lateral and the largest
medial mammary arteries. The teat is abundantly supplied
by arterial papillary retia (sing. rete). The veins originate
from venous papillary retia (networks), which form at the
THE MAMMARY GLANDS
The mammary gland is a modifi ed cutaneous (sweat)
gland. Its function is to produce milk. By defi nition, one
mammary complex consists of one body and one papilla
(teat). The usual number of mammary glands in the goat
is two, under the collective name of the udder. There may
be variations in number. The two mammary glands are
separated outside by an intermammary sulcus.
The udder is attached to and suspended from the ventral
body wall in the inguinal region (see Figures 6.1, 6.4, and
6.5). The udder of the goat is relatively large in comparison
with that of the ewe.
The entire mammary gland is intimately surrounded and
protected by a capsule. A suspensory apparatus supports
the full heavy udder. There are lateral and medial laminae,
connective tissue sheets originating from the tunica fl ava
abdominis, from the symphyseal tendon, and from the
aponeurosis of the external abdominal oblique muscle (see
The Muscular System). From both lateral and medial
laminae, suspensory lamellae enter the mammary glands
at different levels and are able to support the weight of the
udder. The medial laminae are elastic, and this shows when
the udder is full of milk. In a full udder, the two teats look
abducted. The intermammary sulcus drops because of the
elastic tissue of the medial laminae, while the lateral
laminae are inextensible.
The body of each mammary gland is cone-shaped and
ends with a voluminous teat. There is a circular constric-
tion at the transition between the body and the teat. Each
gland consists of glandular tissue and a duct system
(Figure 6.36 a).
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