Dairy Cattle Lactation (Part 1) Flashcards
Lactation
The production of milk by the mammary gland
Mammogenesis
Growth and development of the mammary gland
Galactopoiesis
Maintenance of lactation
Involution
Cessation of milking
Mammogenesis
Zygote → First calving
Only once during development
Positive growth
Mammogenesis
Conception → Drying off
Part of normal reproductive cycle
Positive and negative growth (involution)
Most critical stage in Mammogenesis
Prepubertal
Most growth stage in Mammogenesis
Pregnancy
Mammogenic hormones
E2 , P4, GH , adrenocorticoids , PRL , Lactogen ,insulin,IGFs , Thyroid
Allometric mammary Growth Rate
Faster than the rest of the body
starts at 3-4 months of age and continues after puberty through the first few estrous cycles (until about 1 year of age)
Isometric Mammary Growth Rate
Similar to the rest of the body
After 1 year of age to conception
Over feeding during the allometric phase (especially before puberty) can result in …
excess fat deposition & inhibition of parenchymal growth and future milk production
Mammary tissue in heifers fed ad libitum was …
> 80% fat
Heifers fed a restricted diet have around …
65% fat , and 13% more parenchymal Tissue compared & with heifers ad libitum
Overfeeding during the prepubertal period …
reduces GH levels
GH effect with mammary growth
GH has a positive correlation with prepubertal mammary growth
Mammary development
30 to 40 days of bovine fetus
Initial development
Mammary development
At birth
- Externally teats are present
- Internally, teat cistern + gland cistern + little CT + little fat
Mammary development
Until 1st pregnancy (prepubtal)
↑ CT + ↑ fat + ↑ ducts + Slow growth and development of the teats and duct system
Mammary development
At puberty
E2 stimulates growth and development of the ducts
Mammary development
Puberty to conception
elongation and branching of the ducts + stromal growth (especially blood vessels)
Most of the mammary growth … occurs during pregnancy
45-90%
Mammary development
Early pregnancy
ductal growth
Mammary development
Mid to late pregnancy
Alveolar development
Mammary development
Last month of pregnancy
Colostrum secretion
Ducts differentiate into
milk secretory cells (lobule-alveolar system)
The duct network occurred until puberty will determine the extent of lobule-alveolar development during gestation
Mammary development
Early lactation
Number of milk secreting cells reaches a maximum at Peak lactation (40-70 d), then
declines towards the end of lactation
Lactogenesis
A process of differentiation by which the mammary alveolar cells acquire the ability to secrete milk (Milk contents) i.e. convert & from a now-secretory state to a secretory state
Lactogenesis I
associated with limited secretion (colostrum secretion)
Lactogenesis II
Associated with copious milk secretion shortly before parturition and postpartum
