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Anatomy of the mammary gland

The gross anatomy of the mammary gland differs a lot amongdifferent species. The number of glands and teats are not the same

for the cow, the sow or the horse. However, the microscopicanatomy is very similar among species.

The development of the mammary gland starts early in the foetallife. Already in the second month of gestation teat formation startsand the development continues up to the sixth month of gestation.When the calf foetus is six months, the udder is almost fullydeveloped with four separate glands and a median ligament, teatand gland cisterns.

The developments of milk ducts and the milk secreting tissue take

place between puberty and parturition. The udder continues toincrease in cell size and cell numbers throughout the first fivelactations, and the milk producing capacity increasescorrespondingly. This is not always fully utilized, since theproductive life time of many cows today is as short as 2.5lactations.

The mammary gland of the dairy cow consists of four separateglands each with a teat. Milk which is synthesized in one glandcannot pass over to any of the other glands. The right and left sideof the udder are also separated by a median ligament, while thefront and the hind quarters are more diffusely separated.

The udder is a very big organ weighing, around 50 kg (includingmilk and blood). However, weights up to 100 kg have beenreported. Therefore, the udder has to be very well attached to theskeleton and muscles. The median ligaments are composed ofelastic fibrous tissue, while the lateral ligaments are composed ofconnective tissue with less elasticity. If the ligaments weaken theudder will become unsuitable for machine milking since the teatsthen will often point outward, demonstrated in the picture below.

The mammary gland consists of secreting tissue and connectivetissue. The amount of secreting tissue, or the number of secretingcells is the limiting factor for the milk producing capacity of theudder. It is a common belief that a big udder is related to a highmilk production capacity. This is, however, not true in general,since a big udder might include a lot of connective and adiposetissue. The milk is synthesized in the secretory cells, which arearranged as a single layer on a basal membrane in a sphericalstructure called alveoli. The diameter of each alveoli is about 50-250 mm. Several alveolies together form a lobule. The structure ofthis area is very similar to the structure of the lung. The milk which

is continuously synthesized in the alveolar area, is stored in thealveolies, milk ducts, udder and teat cistern between milkings.

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