Transcript 2002 ANS 110

Milk synthesis
Milk synthesis
• Proteins – major groups are caseins and
whey proteins
• Lactose – unique to mammary gland
• Fat – droplets enveloped by membrane
– Ruminants – fatty acids synthesized from
volatile fatty acids (acetate)
Milk ejection
• Milk “letdown”
• Neuroendocrine reflex
• Milk not removed solely
by suckling action
– Passive removal possible
from gland cistern
• Controlled by
myoepithelial cells
– Oxytocin stored in posterior
pituitary gland
• Action within 30 – 60
seconds
Milking Equipment
• Pulsation system alternately…
– Introduces atmospheric air into hoses and teat
cup chamber
– Removes air from system
– Pulsation rate = # of cycles of alternating
negative and atmospheric pressure; ~ 50
cycles/minute
Milking
Expansion Phase
Massage Phase
Milk ejection II
• New milk synthesis inhibited after ~ 18 h of
milk non-removal
• Complementary or residual milk (10- 20%
of total)
• Inhibition
– Stress, emotional upset
• Administration of exogenous oxytocin
Involution
• 45 – 60 d in dairy cows
• “Regression” & “remodeling” in the
mammary gland
– Decreased metabolic activity
– Altered size, shape, # of alveoli
• Length of dry period influences subsequent
lactational performance
Decreasing milk production
• Lack of milk removal
–
–
–
–
Pressure builds up in gland
FIL: chemical signal in milk to cells?
After 16-18 h, milk synthesis decreases
Important to avoid in early lactation
• Mastitis leading to development of scar
tissue
Bovine Somatotropin
• Increase milk yield ~ 10 lb per cow
• Increases nutrient utilization by the mammary
gland
• Milk yield
– increases gradually during rbST supplementation, up to
max ~ d 6
– Administration after peak milk yield
• Increased costs: labor, rbST, DMI
– Increase in DMI lags behind MY
Milking 4x or 6x
• Milking frequency: ~ 8 lb per cow
– Early in lactation: increased peak and
persistency
– Milk fresh cows first and last at each milking
for first 21 d
– Increased labor, use of milking equipment, feed
costs -- 0.5 lb DM for 1 lb milk
Photoperiod--Lactation
• 16 to 18 h light per day increases MY 5 to
15%
– Low investment, size neutral
• Barns are traditionally dimly lit
• Estimate # of fixtures needed to increase
lighting
• Cleaning required
Photoperiod – Dry Period
• Cows on 8 h vs 16 h during dry period
produced ~ 7 lb/d more milk during early
part of subsequent lactation
Cow health issues – transition
period
• Milk fever (parturient
paresis)
• Ketosis
• Retained placenta
Displaced Abomasum
Normal
Left
DA
Right
Mastitis
• Infectious disease
• Inflammation of
secretory tissue
Classification
• Clinical
– Shorter duration
– Causes visible changes in udder and milk
– Acute cases – become systemic infections
• Subclinical
– Longer duration
– Majority of mastitis cases
– May be chronic
Detection of mastitis
• Appearance of milk
• Somatic Cell Count
– Leukocytes & epithelial (secretory) cells
• leukocytes
• secretory cells
• California Mastitis Test (CMT) – detects
DNA in milk
• Bacteriologic testing