1
Q
lactation
A
- the production of milk by the mammary gland
- characteristic of all mammals
2
Q
mammary gland function
A
- provide milk (colostrum) to nourish offspring
- to provide passive immunity to the offspring via colostrum
- to physiologically influence gut development
- to promote intestinal colonization by non pathogens ( beneficial bacteria)
3
Q
mammary gland structure
A
- composed of collections of spherical sacs called alveoli
- made up of a single layer of glandular cells that synthesize milk and secrete it into the lumen
- each alveolus has its own blood supply from which milk constituents (fat, protein and water) are obtained
- milk production is directly related to the amount o blood flowing through mammary gland (yield directly proportional to the blood flow )
- 600L blood = 1 L milk
- 30 kg daily milk yield = 9L/min mammary blood flow
4
Q
mammary gland anatomy
A
- each alveolous is also surrounded by myoepithelial (muscle) cells
- during milk let down, these contract and force the milk out of the lumen of the alveoli into a duct system
- oxytocin causes the myoepithelial cells to contract
- alveoli are arranged in groups = lobules and and groups of lobules are lobes
- milk is forced into the duct system and collects in a large reservior = udder cistern
- from the udder cistern milk goes intothe teat cistern
5
Q
bovine suspensory system
A
- the bovine udder is composed of 4 separate mammary glands
- each supported by several suspensory ligaments
- median suspensory ligament is the most important
- suspensory bligaments support the weight pf the udder
- udder weighs 20 kG
may contain another 20+ kg of milk - total weight = 40 + kg
6
Q
mammary gland anatomy of rat, pig and human
A
- large ducts from a # of lobes lead directly to the nipple
- multiple ampullae provide limited milk storage similar to udder cistern
7
Q
mammogenesis
A
- mammary gland anatomy development
8
Q
lactogenesis
A
- initiation of milk synthesis
9
Q
galactopoiesis
A
- milk synthesis (maintenance)
10
Q
mammogenesis at birth
A
- the bovine udder has both teat and gland cisterns but the major duct system is little developed
11
Q
mammogenesis - birth to immediate pre pubertal period
A
- mammary gland growth is isometric
- largely connective tissue and fat
- very little duct development
- overfeeding = results in fat deposite in mammary pad which will prevent mammary development
- this can result in a reduction in subsequently milk yeild up to 30%
- effects may persist into the third lactation
12
Q
mammogenesis - at the time of puberty
A
- ovarian follicles produce estrogen ( stimulating growth of the udder cistern and ducts)
- corpus luteum produces progesterone ( stimulates growth of the alveoli
- estrogen and progesterone act in concert ( limited effect if adrenal or pituitary glands removed
- other hormones important for full mammary development
- growth hormone, thyroid hormone thyroid hormones and adrenal steroids (cortisol)
13
Q
mammogenesis - during pregnancy
A
- mammary development continues under the influence of estrogen and progesterone
- the duct system develops during the major part of pregnancy
- alveoli develop mostly towards the end of pregnancy
14
Q
lactogenesis - around the time of calving
A
- secretory cells of the alveoli start to produce milk because:
- surge of prolactin and decrease in progesterone around partition is the signal to start lactation
- lactose synthase
- a lactalbumin synthesis is induced by hormonal change ( withdrawl of progesterone )
- galactosyl transferase a lactalbumin complex
- lactose is major osmotic drier that determines milk volumn
- draws water in which is a large % of milk and will bring up yeild and volume
15
Q
galactopoiesis - at calving and beyound
A
- the important hormones for milk synthesis
- prolactin: higher levels on long photoperiod ( 16 h light and 8h dark)
- growth hormone
- insuling like growth factor ( IGF 1 )
16
Q
important differences between species
A
Prolactin:
- lactogenesis in ruminants is more sensitive to PRL than is galactopoiesis. milk production is set at lactogenesis and is less responsive to PRL stimulation following galacto poiesis
- suckling intensity and frequency in monogastric pigs stimulates prolactin secretion increasing milk yeild - the hungerier the piglets the more milk the sow will produce
GH
- a galactopoietic hormone in ruminants
17
Q
lactation cycle in cattle
A
- 4 phases
dry period: development of the small ducts and alveoli especially near calving
around calving: diffrentiation of alveoli cells into actively secreting cells ( lactogenesis )
lactation: all cell activity direclty towards milk synthesis and no further mammary growth ( galactopoiesis )
involution of the mammary gland starting after peak lactation ( this is during lactation ) - gradual, but irriversible regression of the gland, a reduction in the number of active alveoli
- slow rate of mammary involution = high persistency
18
Q
what happens after the peak of lactation
A
- acceleration by the progesterone of pregnancy
- more pronounced in late lactation
- rapid at drying off
19
Q
lactation cycle
A
- daily milk production in cattle typically increase during the first few weeks of lactation
- peak milk yield in cattle is usually achieved at about 4 to 8 weeks
- production then decreases slowly during the rest of lactation
- due to gradual mammary gland involution
- same pattern of milk yield is aldo observed in sows and mares
- monogastric species are responsible to PRL stimulation and will increase milk production to meet demand
20
Q
drying off
A
- dairy cows - 60 days before next calving
- mammary gland involution and renewal of alveoli
- not necessary but improves yield of subsequent lactation
- reduce diet quality abd stop milking
21
Q
weaning
A
- beef cows, sows, sheep, pigs and dogs
- removal of offspring ends milk removal
- diet quality also reduced
22
Q
insulin and lactation
A
- synthesized and released from pancreas
- primary regulator of blood glucose levels ( increased blood glucose levels stimulate release, lower blood glucose reduces release)
- promotes glucose clearance into adipose and muscle
- in adipose tissue insulin:
- promotes lipogenesis and prevents lipolysis
in muscle tissue insulin - ## promotes glucose uptake, amino acid transport and protein synthesis ( anabolic)
23
Q
milk let down
A
- a neuro hormonal reflex
- suckling stimulates or massaging of udder stimulates somatic nerves in the teat
- signal to the posterior pituitary gland and causes the release of the hormone oxytocin
- oxytocin causes the myoepithelial (muscle cells) around the alveoli to contract
- contraction squeezes the alveoli and forces milk out into the duct system
24
Q
what can inhibit milk let down
A
- stress
- causes release of epinephrine from the adrenal gland
- constricts the blood vessels of the alveoli and so prevents oxytocin from reaching the myoepithelial cells
- there is also inhibition of oxytocin release from the posterior pituitary
25
milk fat and protein
- milk fat forms globules (98-99% triglycerides)
- homogenization produces very small globules which do not separate (rise)
- milk protein ( casein and whey proteins)
26
factors effecting milk composition
- colostrum vs mature milk
- milk protein percent
- milk fat composition
- milk fat percent
27
colostrum
- given in the first milk delivery to a newborn
- most of the protein present is antibodies ecessary for developing immunity
- also contains immune cells that probably help establish the neonate immune system
- also contain high levels of vitamins A E carotene and riboflavin
- lactose vitamin D and iron are all low compared to normal milk
28
what happens is colostrum is not given or if fake milk is given
-gut will only stay open for 24 hours to gain the antibodies for colostrum
- after 24 hours or if fake milk is given, the gut will close and kick start hormone responsiveness without having the proper antibodies
29
immunoglobins
- systemic passive immunity prior to gut closure
- intestinal lumen protection for remainder of lactation
30
lactoferrin
- binds to iron making it more available to the neonate but unavailable for bacteria
- partial digestion products are bactericidal/bacteriostatic
- partial digestion products are immuno stimulatory
31
what happens if pigs orally injected with iron
- its not protected by lactiferin so it adds to e coli replication instead of killing it
- so its injected into the neck
32
lymphocytes and macrophages
- immune cells which may aid in development of neonate immune system
33
oligosaccharides
- short chain sugar molecules
- function as preferntial nutrient substrate for beneficial bacteria
- may function as alternate binding site for pathogens
34
mastitis
- inflammation of the mammary gland
- typically caused by a bacterial infection
35
mastitis effects
- increased white blood cells in milk (neutrophils)
- destruction of alveoli
- bacterial attachement - infiltration of white blood cells
- reduced milk production during infection, following infection due to loss of alveoli
Animal Physiology
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