Slide Set 16: Factors Affecting Milk Composition

Question 1

___ is the most variable milk component while _____ and ____ are the least variable

Answer 1

fat is the most variable milk component while lactose and minerals are the least variable

Question 2

What are the factors affecting milk composition

Answer 2

1. genetic and breed factors
2. stage of lactation
3. nutritional factors
4. milking practices
5. diseases
6. environmental factors

Question 3

Effects of genetics on milk composition

Answer 3

concentrations of milk fat, protein and lactose are genetically controlled to a considerable extent 
milk fat = 0.6
milk protein = 0.6
milk lactose = 0.55
milk yield = 0.3

Question 4

Genetic correlation

Answer 4

solid non fat and protein %, r=0.8
fat and lactose %, r=0.1
milk fat and protein r=0.45
milk yield and fat r = -0.2

Question 5

Which has more total solids, colostrum or transitional milk?

Answer 5

colostrum

Question 6

How do changes during milking affect milk composition?

Answer 6

milk removed at the beginning of milking contains less fat (1-2%) than milk removed at the end of milking (5-10%)
residual milk contain up to 20% fat 
2 phases:
- aqueous phase
- lipid phase (more specific gravity)

Question 7

residual milk

Answer 7

cannot be harvested by milk machine highest fat percentage

Question 8

How does season and temperature affect milk yield?

Answer 8

• mainly due to changes in feed (pasture vs dry feed) and stage of lactation
• in temperate regions, milk during summer contains lower fat (0.4%) and protein (0.2%) than during winter
• high ambient temperature (>30%) reduces lactose %, and SNF % and increases fat %

Question 9

How do nutritional factors affect milk yield?

Answer 9

1. underfeeding
   - decrease milk yield, lactose %, and increase fat %
   - nutritional strategies that increase milk yield usually decrease milk fat %
2. feeding frequency
   - less frequent feeding (especially if concentrate is fed separately) tend to depress milk fat %
   - effect of feeding frequency on milk fat % is affected by level of intake, level of concentrates and stage of lactation
3. forage: concentrate ratio
4. level and quality of dietary protein
5. feeding protected amino acids
   - increase casein %
   - permits the AA requirements to be met with less dietary nitrogen
   - allows for better dietary protein utilization

Question 10

milk protein % might remain constant but significant changes can occur in the ratio of casein:NPN. What are the reasons for this?

Answer 10

1. high levels of rumenally degraded protein

2. imbalance energy: protein ratio

Question 11

What happens to casein during mastitis?

Answer 11

decreases due to reduced synthesis

Question 12

What happens to lactose during mastitis?

Answer 12

decreases due to reduced synthesis

Question 13

What happens to fat during mastitis?

Answer 13

decreases due to reduced synthesis

Question 14

What happens to total solids during mastitis?

Answer 14

decreases due to reduced synthesis

Question 15

What happens to whey protein during mastitis?

Answer 15

increases due to leakage from blood

Question 16

What happens to Cl and Na during mastitis?

Answer 16

increases due to leakage from blood

Question 17

Describe the fate of dietary protein in ruminants

Answer 17

degradable protein is digested into NH3 and peptides that promote microbial growth and there will be more fibre digestion that leads to VFA and feed into mammary substrate to protein and fat biosynthesis

ruminal undegraded protein will be absorbed in the intestines as AA and taken up by the mammary gland for protein and fat biosynthesis