QUIZ THURSDAY

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QUIZ THURSDAY

• LIPIDS / FATS!

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• Animal Science 337 Extra Credit 3
• Look at the handout that shows milk composition
  of different species. Look at species with high
  and low lactose and compare other components.
  Also, why would you expect other components to be
  associated positive or negative to lactose? (7
  pt)
• Some people react to cows milk and it is stated
  that they are lactose intolerant. When they
  change to goat milk, they feel better. Is it
  psychological or real and does lactose drive this
  response? If not, then what? (6 pt)
• I want more Calcium in milk products naturally?
  Can I do it with diet? Answer either way
  /justify! (7)
• DUE BEFORE SPRING BREAK

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Physical and Chemical Properties of Mammary
Secretions

• Dr. Howard Tyler
• AnS 337
• Lactation Biology

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Teleological Approach

• Energetically driven processes are developed to
  provide a benefit
• Synthesis of some components
• Active transport of some components
• Milk itself
• Colostrum
• Needs of both dam and offspring

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Importance to Newborn

• Shift from placentation to lactation
• Provide for nutritional needs
• Regulate developmental processes
• Enhance immunological status
• In ruminants, reticular groove development
• Milk as by-pass feed

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Composition of Secretions

• Determined by stage of lactation
• Composition always in transition
• speed of transition determines degree of
  precision
• Colostrum is rapid transition
• Refers only to secretions present at parturition
• Transitional milk slower transition
• 3-14 days
• True milk composition also changes

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Colostrum and Milk Composition(150 samples)
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Changes in Transitional Milk
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Transition From Colostrum to Milk

• Changes during first 12 hours most dramatic
• Milk secretion begins immediately after
  parturition
• Solids-not-fat composition remains stable for
  transitional milk
• Fat content most variable
• Changes in cell populations very dramatic
• Changes in hormones and peptides very dramatic

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Major Factors Affecting Milk Composition
Completeness of milking Milk removal 4 min.
for a cow removed Time (sec)
Milk Fat Fat
30 16 7 1.4 60 41 18 1.6
120 83 61 4.8 240 100 100
11.1 Fat globules tend to clump,
passage through ducts is retarded/slower
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Fat
Proteins
Sugar
Composition of milk
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Foremilk and Hind Milk ..

• Fats provide satiety
• High fat in the hind milk ensures that the
  neonate feels full after suckling
• Low fat in foremilk encourages consumption

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Physical Composition

• Components in true solution
• The dispersion of particle lt 1 nm in liquid
• Lactose, soluble minerals, NPN
• Components in colloidal suspension
• Dispersion of particle sizes between 10-100 nm in
  liquid
• Proteins, insoluble minerals
• Emulsified components
• Substances or particle size 10-100 microns
• Fats

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Characteristics of Secretions

• Osmolality around 0.3 M
• Very little change in freezing point
• Colostrum
• Highly viscous (albumin)
• Low surface tension (helps fat suspension)
• Low electrical resistance (high chloride content)
• High buffering capacity (although pH is lower)

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Coagulation of Secretions

• Casein coagulates as pH decreases or temperature
  increases
• When pH falls below 5.1, casein destabilizes
• Below 4.5 casein salts form and milk curdles
• Milk forms hard curds
• Slow release nutrient delivery
• Cheese making properties dependent on this
• Colostrum forms soft coagulum
• Very slow release nutrient delivery
• Destroys cheese making properties

Calcium phosphocaseinate neutral casein
Ca (curd) (whey)
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Effect of Rennin

• RENNIN (chymosin) enzyme derived from stomach
  of milk-fed calves
• Rennin causes milk to clot prior to digestion
• Sold commercially as rennet (crude extract) for
  the coagulation of milk to make cheese, ice cream
  and puddings