ANSC 438 Home / Beginning / Milk Composition / Mammary Structure
Mammary Development / Mother & Neonate / Lactation / Mastitis

Independent Study

Mammary Macro-structure
Dairy Cow Udder Anatomy


Blood vascular system - The blood supply to the mammary gland is extremely important for mammary function! All of the milk precursors come from blood. On avg. 400 - 500 units of blood passes through the udder for each unit of milk synthesized by a high producing dairy cow; that is ~280 ml per sec.

High producing dairy goats have a lower (460:1) ratio of blood flow through the gland:milk produced, compared with low producers (1000:1). This means that the amount of blood flow through the mammary gland may by similar for the high and low producing goats, but the efficiency of extraction of the components from the blood while it passes through the udder very is important. This principle is probably similar for cows.

Total udder blood volume for lactating cows about 8% of total body blood volume, while for a non-lactating cow it is about 7.4%. There is a 2-6 fold increase in blood flow in the mammary gland starting 2-3 days prepartum. The decrease in production with advancing lactation is not due to decreased blood flow, rather it is due to the loss of secretory epithelial cells through a process programmed cell death (apoptosis).

Arterial system - Blood leaves the heart and flows towards the rear of the cow by the abdominal aorta. When it reaches the pubic area of the animal the vessels are called the common iliac arteries. These divide into the internal and external iliacs. The external iliac becomes the femoral artery (supplies leg muscles). A branch off of the femoral divides into the caudal epigastric artery and the external pudic (or external pudendal) artery. This artery then passes through the inguinal canal and out of the body cavity. The inguinal canal is the orifice in the body cavity in the inguinal region where blood vessels, lymph vessels and nerves enter and leave the body cavity to supply the skin in the posterior part of the animal (again, the mammary gland is a skin gland). As the external pudic artery passes out of the body cavity it divides into the and the mammary artery (~1cm dia.). Once it enters the gland, the mammary artery then divides into the anterior and posterior mammary arteries, then it further branches as it descends down into the gland.

Udder with major arteries and veins drawn in. Mammary artery and vwin as they exit the body cavity.
Diagram showing location of arteries (red) and veins (purple) leaving the body cavity through the inguinal canal (white circle). Green circle indicates location of supramammary lymph nodes. The mammary vein and mammary artery are shown here on the carcass of a cow after the udder has been cut away. These vessels exit the body cavity through the inguinal canal.

Perineal artery- A small amount of blood also reaches the mammary gland by the perineal artery (from the internal iliac), but this only supplies the upper rear portion of gland.

Sigmoid flexure - Just below the inquinal canal, the pudic artery forms an S-shaped flexure. This allows for downward distention of the udder as it fills with milk, without stressing the blood vessels.

There is essentially no cross over of blood supply between udder halves (there are a few minor exceptions)

Venous system - Veins leave the mammary gland anti-parallel to the arteries. There are three veins on each side that carry blood away from the gland:

  1. External pudic vein leaves the udder parallel to the external pudic artery (2-3 cm dia.).
  2. Subcutaneous abdominal vein (milk vein) exits the gland at the anterior end of the front quarters and passes along abdominal wall (1-2.5 cm dia.). This is the large vein that is visible under the skin on the belly of he cow. It enters the body cavity at the xiphoid process via "milk wells", and eventually empties into vena cava.
  3. Perineal vein leaves the rear of the gland parallel to the perineal artery (0.5 cm dia.). Carries less than 10% of blood leaving udder.

Venous circle - Formed by anastomoses between anterior and posterior mammary veins. Prevents pinching off of areas of venous outflow when the cow is lying down.

Mammary Structure