Lecture 19

What is the function of mammary glands in mammals?

To produce milk to feed young offspring.

What type of gland is a mammary gland?

It is an exocrine gland, specifically modified cutaneous sweat gland.

What is another term for the projection of a mammary gland through which milk flows?

Nipple or Teat.

What is the term for a collection of mammary glands, particularly in species with more than two?

Dug.

How do mammary glands form

Mammary ridge of epidermal tissue → bud formation which invaginates into the dermis → bud develops more buds forming branches → canals/channels begin to form which eventually form the ducts

What do myoepithelial cells do in the mammary gland?

They surround terminal portions of the developing gland and contract to help squeeze out milk.

Which mammalian species don’t have mammary glands

Male horses and rats

Where are mammals located in different species

Primates = thoracic region where they can nurse their young

Dogs, cats, rabbits etc = abdominal region

Flight species = inguinal region

What is the generalised structure of a cow udder

The udder is a compound tubuloalveolar gland with numerous lobules of secretory units and a duct branching system. The mammary glands contain stromal tissue (secretory tissue and ductal tissue) and parenchyma

The lobules are separated by a connective tissue septa

What is the pathway by which milk travels

Secretory units → small intralobular ducts → large ducts → lactiferous ducts → gland sinus (cistern) → teat sinus (cistern) → teat canal → exterior

How do hormones influence the growth of mammary glands

Oestrogen, growth hormones, adrenal steroids and progesterone and prolactin are involved in growth of the ducts whilst prolactin and adrenal steroids are also involved in milk secretion

What is the smallest secretory unit in the mammary gland

Alveolus lined with cuboidal epithelium

What are the supporting ligaments of the udder

Lateral suspensory ligament → branches off medial ligament and runs around the udder

Medial suspensory ligament → separates two halves of the udder

• Has 2 layers

• Lamellar plate = comes of the medial ligament → adds support to glands

What is the arterial supply to the udder

External pudendal from the inguinal canal in a sigmoid flexure pathway

Ventral perineal from the pelvic canal

What is the venous drainage of the udder

An anastomosis of:

Milk vein = superficial cranial epigastric vein

External pudendal vein

Perineal vein (minor contribution)

What is the lymph drainage of the udder

mammary lymph nodes/superficial inguinal lymph nodes → These feed to the medial iliac lymph nodes

What is the nerve innervation to the udder

1st and 2nd lumbar nerves supply the skin cranially

Peroneal nerve supplies the skin caudally

Genitofemoral nerve supplies the internal, deeper tissues

What are the constituents of milk that provide energy and protein?

Lactose, oligosaccharides, protein, fat, and cells.

What is the difference between lactose and oligosaccharides

lactose is a disaccharide sugar composed of glucose and galactose, specific to milk and is the main driver of milk volume, while oligosaccharides are a class of carbohydrates made up of several simple sugars that are not important economically

How much lactose is usually in cow milk

4.5-5%

How much protein is usually in cow milk

3.5% but varies immensely

What are the two types of proteins important in milk

• Caseins

  • Unique to milk

  • Insoluble

• Whey proteins

  • Albumins

  • Globulins

What is the % of fat in milk 

Bovine milk 3-6% fat

Why is fat content economically important for farmers

Fat content affects milk pricing and profitability, as higher fat milk typically commands better market prices

What is unique about the synthesis of fat in milk

Not synthesised in mammary gland – they come from rumen and liver and are transported into milk by mammary epithelial cells

What is the difference in BMCC and ICCC in milk

BMCC refers to Bulk Milk Cell Count, which indicates the number of somatic cells in milk, while ICCC refers to Individual Cow Cell Count, which measures somatic cells per cow.

Want BMCC <250 000 cells per ml and ICCC of 50 000 - 250 000 per ml

What causes milk letdown and production. How is it inhibitied

Suckling stimulates nerve stimulation and oxytocin release → myoepithelium contracts → milk release. Ejection causes a reflex via vasointestinal active peptide → dopamine suppression → prolactin surge → induces secretion from secretory tissue (production)

Oxytocin is inhibited by adrenalin → constricts capillaries

What does colostrum contain that is crucial for newborns such as calves and foals

Antibodies

High in vitamin A

High in fat → energy

High in antibodies

Not high in carbohydrates

High in other vitamins

What causes colostrum production

Colostrum is produced during lactogenesis in the absence of milk removal + presence of progesterone

= Prolactin + progesterone

What is mastitis and why is it economically significant?

It is an infection in the udder that can cost the Australian dairy industry significant losses.

What are the three forms of mastitis?

Subclinical, Clinical, and Toxic.

How do you differentiate between the three forms of mastitis

• Subclinical

  • Changes in milk but they are not visual

  • High cell count

• Clinical

  • Clinical signs + changes in the milk

    • Hot udder

    • Swollen udder

    • Clots in milk etc

• Toxic

  • Whole cow is affected not just udder

    • Tissue damage

    • Gangrenous areas etc

What skin condition can you see due to machine rubbing on teats

Hyperkeratosis

What are the key components assessed in milk testing?

Normal components like protein, fat, volume, and abnormal components like cells and contaminants.

What are intramammary treatments used for? What types are there

To treat or prevent mastitis in cows.

• Lactating cow – for treating clinical mastitis during lactation

• Dry Cow Therapy – for treating subclinical mastitis at the end of lactation

• Teat sealants – for sealing the teat at the end of lactation and preventing infection