Milk constituents

Question 1

Primary constituents of milk

Answer 1

• Fat
• Proteins
• Lactose
• Minerals
• Water

Fat, protein and lactose are commonly recorded in the UK

Question 2

Average % for each constituent in the UK milk industry

Answer 2

• 3.65% fat
• 3.2% protein
• 4.7% lactose

Question 3

Reasons for changes in fat content

Answer 3

• seasonal variation: summer months averaging 0.4% units less than winter months
• vary with stage of lactation: highest % found in colostrum, followed by a decline during the 1st 2m of lactation, then a slow increase as lactation progresses

Question 4

Reasons for changes in protein content

Answer 4

• age: declines in cows older than 3y, with a 0.4% drop being reported over 5 lactations
• stage of lactation: colostrum is very rich on protein, total protein rapidly falls during the 1st few days of transition from colostrum to normal milk, reaching a minimum about 5-10w into lactation

Question 5

Reasons for changes in mineral content

Answer 5

• colostrum has higher mineral composition
• inorganic phosphorus levels were shown to be higher in 1st lactation cf multiparous cows
• milk phosphate levels lowest during the summer