Anatomy of the udder and clinical consequences. Defense mechanisms of the udder in cattle

Question 1

Anatomical composition of the mammary gland

Answer 1

• Modified sweat gland and ectodermal in origin
• In cow : 2 glands
    o Separated medially by a double septum
• 1 gland made of :
    o Body
    o 2 papillae / teats
• No physical barrier between quarters
• No common canal of the quarters
• No common blood supply
• 400 L blood 1L milk
• Weight: 50-75 kg

Question 2

Secretory unit of Udder

Answer 2

• Mammary parenchyma composed of connective tissue, areolar tissue and secretory epithelial cells
• Amount of interstitial tissue may be considerable compare to secretory tissue
o Large udders but very low milk production capacity
• Trabeculae extending from capsule divide the gland parenchyma in lobes and lobules

Question 3

Secretory unit of Udder

Units

Answer 3

• Lobe
o Groups of lobules surrounded by CT sheath
• Lobules
o Clusters of 160-195 alveoli encapsulated by CT sheath
o Alveoli
▪ = Discrete milk producing unit
▪ Ovoid, pyriform or irregular, appears fused at times
▪ Increased number and diameter of alveoli = Maximum production space and holding milk capacity
• Number of teats is different between cow, sow or horse
• But microscopic anatomy is similar

Question 4

Structure of the teat

Answer 4

1. Epidermis
2. Dermis
3. Muscles
4. Endothel

Lenght
• Decreasing in size in lactations 1-3, then stable
• 3 - 14 cm
Diameter
• 2 - 4 cm
Shape
• cone or cylinder shape

Question 5

Structure of the teat

1. Epidermis

Answer 5

• Keratinized cells
• 4-5 times thicker than skin
• strongly attached to dermis
• no hair follicles, sweat glands, sebaceous glands

Question 6

Structure of the teat

2. Dermis

Answer 6

• Blood vessels and nerves
• nerve endings in the epidermis
• Venous plexus at the base of the teat: importance in milking and suckling

Question 7

Structure of the teat

3. Muscle layer

Answer 7

• Circular and longitudinal and oblique layers
• Sphincter muscle around the teat canal
o At milking the teat becomes longer (30-40%), teat canal opens and becomes shorter
o Post milking dipping importance

Question 8

Structure of the teat

4. Endothel

Answer 8

• Strongly attaching cubic epithelial cells
o Immunocomponent cells→Between alveolar epithelial cells
o Bacterium invasion: to help WBC entrance keeping distance for them

Question 9

Mammary gland defense mechanisms

Answer 9

A. Anatomical barriers – FIRST LINE OF DEFENCE
• Teat sphincter muscle
o -closes two hours after milking
• Teat canal during dry off stratified epithelial cells derive a keratine plug
• Keratinized epithel of the teat cistern

Innate immune response
B. Alveolar macrophages (TNF-α, IL-1B)
C. Neutrophil recruitment from the bloodstream

Question 10

Suspension of the mammary gland

Answer 10

• Suspensory apparatus gives firm attachement of uder with the abdominal wall
• Extends caudally and attachs the prepubic tendon→Symphysis pelvina
• Median ligaments are composed of elastic fibrous tissue
• Lateral ligaments are composed of connective tissue→Less elasticity
• If ligaments become weak the milking machine will not be able to take them, they will often point outward