|
COLLECTION: GOAT HANDBOOK
ORIGIN: United States
DATE INCLUDED: June 1992
Extension Goat Handbook
This material was contributed from
collections at the National Agricultural Library.
However, users should direct all inquires about the
contents to authors or originating agencies.
DOCN 000000049
NO F-6
THE UDDER
G. F. W. Haenlein R. Caccese; U. of Delaware, Newark
P. E. Meckley; U. of Delaware, Newark
Anatomy and Physiology
1 The udder of goats consists of two separate halves
with a single gland in each half. The udder is a gland
derived from the skin, and has no direct connection
with the abdominal cavity except through the inguinal
canal, through which strands of blood vessels, lymph
and nerves enter and leave the udder.
2 The size of the udder depends on
age and stage of lactation of the animal but should
be well developed. Viewed from behind, the udder should
appear deep and broad with high and wide attachments.
Ideally, the two halves will be symmetrical, with
a slight cleft between them.
3 Viewed from the side, the back
end of the udder should be well contoured, rounded,
deep, with smooth, strong rear attachments. The fore
udder should extend forward from the teats, merging
gradually into the abdomen on a forward reaching angle.
The lack of good fore udder attachment often leads
to a pendulous looking udder, especially during the
heavy periods of lactation.
4 The udder quality should be free
of lumps and fibrous or ''meaty'' conditions. Each
udder half should have only one teat, although supernumerary
(extra) teats are not uncommon, being located mostly
posterior to the true teat. The size of the teats
varies greatly among goats; some are quite small and
short, making it difficult to milk them; others are
very large, plump, and funnel shaped and even sometimes
with seemingly no apparent point of connection to
the udder.
5 Supporting Structure The separation
of the goat udder into halves and their support is
achieved by the medial suspensory ligament, which
is comprised of two strong sheets of elastic tissue
which attach to the pelvic arch. Strong support from
this ligament is required during the periods of heavy
lactation in order to prevent the formation of a pendulous
type udder. A flat floor to the udder is an indication
that the ligament is in fact weak. A good udder support
should have a slight crease or inverted ''V'' shape
between the teats.
6 The lateral suspensory ligaments
form a fibrous layer on the outer surface of the glands,
joining the medial ligaments on the bottom side of
the udder. Fibrous connective tissue will also penetrate
the glands, joining with the interglandular supporting
tissue, thus lending support to the entire udder.
7 When the udder fills, it stretches
the median suspensories, causing the teats to protrude
outward and downward. This allows for the greatest
expansion of the udder with a minimal amount of dropping
of the udder. Around 400f the milk, that is produced
by the mammary gland, is held in the natural storage
spaces of the udder. The other 60must be accommodated
by stretching of the udder. When and if these ligaments
weaken, the udder will begin to break away from the
abdominal wall.
8 Inner Structure The basic units
of the mammary system are the secretory cells known
as alveoli, or acini. These production sites are extremely
small, having a distended diameter of about 0.01 to
0.03 mm. In a single cubic centimeter of mammary tissue,
over one thousand alveoli could be present.
9 Groups of alveoli are bound together
by a wall of connective tissue that isolates the enclosed
groups into functional units known as lobule. These
lobules are in turn connected together like grapes
by more extensive connective tissue into groups called
lobes.
10 The alveoli are surrounded by
myoepithelial (muscular) cells, which are responsible
for the milk ''let down'' that occurs through the
release of the hormone oxytocin. These cells are also
found throughout the various ducts of the mammary
system. Milk production within the alveoli is inversely
related to the pressure exerted on the alveoli from
the buildup of milk.
11 A series of ductules and ducts,
or milk canals, lead from the lobules and lobes to
the storage area located at the distal part of the
udder, just above the teat, called udder cistern or
gland cistern. It is capable of storing about a pound
of milk, but the majority of milk is retained within
the alveoli, lobules, and ductules.
12 From the udder cistern, milk passes
into the teat cistern, which terminates into the streak
canal, the final passageway. The distal end of the
streak canal is kept closed by a dense, elastic tissue
consisting of circular smooth muscle fibers popularly
called sphincter but being not a true sphincter by
definition. Because of the lack of a true sphincter
muscle, it is possible, although difficult to remove
milk from a goat udder that has not undergone the
let-down reflex.
13 Spreading from the streak canal
up and into the teat cistern is a structure consisting
of several folds of mucous membranes, each having
several secondary folds. This structure, known as
Fuerstenberg's rosette, aids in the retention of milk
within the teat. It also prevents bacterial entrance
into the gland. It functions as a plug and seal, so
that as pressure builds within the udder this rosette
closes off the teat cistern and milk leaking is prevented.
14 Blood Supply The main blood supplies
to the udder are the posterior aorta, the right and
left common iliac arteries, the external iliac arteries
and the external pudic arteries. From the external
pudics, the mammary arteries arise at the base of
the udder. As the arteries pass upward and forward
through the udder, numerous lateral and cranial branches
arise. They break off into finer arteries to supply
the lobules and alveoli.
15 It appears that the size of the
external pudic artery has some determination on the
development and size of the udder. If the external
pudic is severed experimentally, the small arteries
of the udder increase in size. Milk production will
drop off to almost nothing for the first few days,
then gradually return to normal. The return increase
parallels the increase in size of the subcutaneous
abdominal arteries to the anterior portion of the
udder.
16 The volume of blood flow through
the udder in a lactating goat has been estimated to
be 280f the minute-volume of the heart, or 1,200 liters
of blood per day. On the other hand, arterio-venous
difference measurements have established a relationship
of 400 volumes blood for each 1 volume milk, i.e.
for a gallon milking goat it would mean 400 gal blood
flow per day.
17 The venous system is more pronounced
and evident than the arterial system, and blood vessels
that can be seen on the udder or abdomen are veins,
not arteries. The external pudic vein is the principal
component of the venous system, passing back out of
the udder close to the caudal border and into the
abdominal cavity through the inguinal ring, finally
returning to the heart via the posterior vena cava.
18 A second return system is via
the subcutaneous abdominal veins (milk veins) that
run along the abdomen until they pass through the
milk well back into the thorax.
19 The mammary veins develop from
the external pudic veins at the posterior basal border.
They turn forward along the basal surface of the udder
until they merge into the subcutaneous abdominal veins.
20 Lymph System Few studies of goat
lymphatic systems have been done, although it appears
that they may be similar to the lymphatic system of
cattle. The supramammary lymph nodes have been observed
to be located in corresponding locations between goats
and cows.
21 Lactation increases the flow of
lymph through the mammary glands ten-fold. Flow rates
of lymph undergo large variation depending on the
time of day. Mild exercise also elevates the rate
of lymph flow sharply. Suckling or massaging actions
will increase the flow of lymph, but machine milking
does not seem to produce this effect.
22 The mammary lymph of cows, sheep
and goats appears to be basically similar in composition,
with a protein content of about 56-590f plasma values,
decreasing in level before parturition and during
early lactation. Ratios of albumen to globulin are
higher in lymph than in plasma.
23 Nerve Supply The udder of the
goat appears to be supplied by one primary nerve,
the external inguinal, which divides into two branches.
The superficial branch runs to the abdominal muscles
and the deeper running branch passes through the inguinal
ring, following the external pudic artery and vein
in the udder. This branch in turn branches off into
two again. They are termed the ramus medius and the
ramus inferior. At the base of the udder, the ramus
medius divides into 3 branches, the smallest of which
innervates the pudic vein; the larger, ramus papillaris
enters the teat, and the ramus glandularis joins the
larger milk ducts and the udder cistern.
24 The ramus inferior enters the
udder between the external pudic vein and artery,
where the main branch can be traced to the vasuclar
system.
25 The udder is of primary importance
to goat dairymen, thus a basic knowledge of it's form
and function is very valuable.
THE UDDER
COLLECTION;GOAT HANDBOOK
ORIGIN;United States
DATE_INCLUDED;June 1992
|
