Milk synthesis

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Milk synthesis
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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)

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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

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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

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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

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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

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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

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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

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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

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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

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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

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Cow health issues transition period

• Milk fever (parturient paresis)
• Ketosis
• Retained placenta

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Displaced Abomasum

• Normal DA

Right
Left
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Mastitis

• Infectious disease
• Inflammation of secretory tissue

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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

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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