Lactation

1. Mammary Gland Secretions
1. Colostrum
1. First secretion
2. Higher in protein b/c high antibody/immunoglobulin count
3. Critical to newborn survival (immunization)
2. Milk
1. Produced and secreted by mammary gland
2. Composition varies by species (biggest difference is fat content)
3. Structure of mammary glands are similar on the microscopic level in farm animals
2. Mammary Gland Anatomy
1. Glands
2. Teats
3. Canals
4. Cow
1. 4 glands, 4 teats, 1 canal
5. Mare
1. 2 glands, 2 teats, 2 canals
6. Ewe
1. 2 glands, 2 teats, 1 canal
7. Sow
1. 4-9 glands, 4-9 teats, 2 canals
2. The more the better
3. Mammary Gland Development, Anatomy and Function
1. Prenatal period
1. Structures of mammary gland develop
2. Puberty
1. Estrous cycle begins
2. Progesterone and estradiol stimulate growth of mammary gland
3. Hormone PROLACTIN important
1. Close to birth, is secreted
2. Enables mammals to produce milk
4. At parturition
1. Levels of progesterone and estrogen decrease and lactogenesis occurs
5. Lactogenesis
1. TWO STAGES
1. Stage I Lactogenesis
1. Immunoglobulin uptake occurs and colostrum is formed, much of this prior to birth
2. Stage II Lactogenesis
1. Copious milk secretion begins,  milk of normal composition is produced
6. Mammary Gland Morphology
1. Alveoli- primary structure
1. Secretory cells
1. Absorb nutrients
2. Transform nutrients from blood
1. Lactate, fat, and protein
3. Move milk into lumen of alveoli
1. (Lumen=inner space of a tubular structure)
2. Arranged in lobules
3. Drained by ductwork
7. Milk Synthesis
1. 400 vol blood: 1 vol milk
2. Alveoli surrounded by capillaries
3. Major components formed in epithelial cells
1. Epithelial cells/secretory cells/alveolar cells are THE SAME THING!!!!!!!!!!!!
8. Milk Release/Letdown
1. CNS stimulus
1. Can be conditioned
2. Used in the milk industry
3. Pressure of fetus on CNS causes this stimulus
2. Release of oxytocin from posterior pituitary
3. Contractions of myoepithelial cells- causes milk to be squeezed down to teats
4. Move milk into duct system
1. Duct ---> Gland cistern ---> Teat cistern ----> Streak canal -----> Teat sphincter
9. Lactation Curve
1. Milk production peaks, then declines
1. Cows 50-60 days
2. Peaks quickly, declines gradually
2. Involution
1. Decrease weight, volume
2. Mammary gland must go back to pre-lactation state
3. Involution reversed w/ next pregnancy
10. Mastitis
1. Inflammation of mammary gland
2. Usually bacterial
1. Requires antibiotics
2. Causes wasted milk
3. Can cause cellular damage to mammary tissue
11. Milk Composition
1. Carbohydrates
1. Lactose
2. Protein
1. Casein
2. Sometimes mother will put protein into milk faster than she can consume it, go to body reserves
3. Lipids
1. Milk fat
2. Variable
4. Calcium
1. Milk fever- disease characterized by reduced calcium in blood when calcium demand exceeds calcium intake; results in poor muscle function, weakness, etc.
12. BST
1. Bovine somatotropin
2. Made with rDNA
3. Partitions nutrients
4. Increases amount and efficiency of milk production
5. Must be injected
6. Species specific
7. Peptide hormone, used as a growth hormone- increases milk
8. Not allowed on the market
9. Protein hormone
10. Taken from pituitary gland
11. Able to be produced commercially
12. It's OK, doesn't make much of a difference to the milk
13. Increases amount and efficiency of milk production

HORMONES:

Prolactin- enables milk production

Progesterone and Estrogen- decrease leads  

to lactogenesis