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ORIGIN: United States

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
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.

ORIGIN;United States


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