Dairy Cattle Feeding Standards: Protein

Question 1

The sum of what endogenous protein losses (EPL) is the net protein requirement for maintenance?

Answer 1

• Sum of:
• urine (EUP)
• faeces (EFP)
• dermal
• If milk were to be included, this would be production, as milk is a form of production

Question 2

What is the equation for endogenous urine protein loss (EUP)?

Answer 2

EUP = 37log₁₀W-42.2

Question 3

What is the equation for endogenous faeces protein loss (EFP)?

Answer 3

EFP - 15.2g/kgDMI

Question 4

What is the equation for endogenous dermal protein loss?

Answer 4

Dermal = 0.11g/kgW^0.75

Question 5

How is the net protein required for lactation calculated?

Answer 5

from amount of protein in 1L of milk
eg Friesian 35g/kg milk
Jersey 38g/kg milk

Question 6

How much protein is gained from live weight loss (LWL)?
At what efficiency is it used?

Answer 6

• Protein from LWL (g/kg LWL) = 309.1 - 29.5CS
• Used w/ 75% efficiency
• 1kg LWL provides energy for over 6kg milk, but only protein for 3.5L milk
• may need to consider UDP

Question 7

What are the constraints on the use of Microbial Crude Protein (MCP)?

Answer 7

• Limit to amount of RDP a cow can use
• depends on energy intake
• More energy = more protein used
• When sufficient N supplied
• MCP yield will vary depending on fermentable energy intake
• More energy = more MCP
• Any additional amino acid requirements (e.g. for high producing cows) must be met by Undegradable Dietary Protein (UDP)

Question 8

Predicting MCP
What % MCP does the currently used SCA (1990) system assume leaves the stomach as true protein?
What % is digested?

Answer 8

Assumes 80% leaves stomach as true protein (PLS)

Assumes 70% of this is digested (DPLS)

Question 9

Predicting MCP
What % MCP does the CSIRO (2007) system assume leaves the stomach as true protein?
What % is digested?

This is the more correct figures though not currently used in practice

Answer 9

PLS is 85%

DPLS is still 70%

Question 10

What is metabolisable protein (MP)?
What does it depend on?

Answer 10

• Crude protein absorbed from intestines as amino acids
• Will depend on
• Amount of MCP leaving the stomach as protein (PLS)
• Digestibility of MCP leaving the stomach (DPLS)
• Digestible undegradable dietary protein (DUDP)
• PLS is assumed as 0.8 x MCP (0.85 in 2007 feeding standard)
• Digestibility of PLS and UDP is assumed as 0.7 unless otherwise known

Question 11

What does the efficiency of use of metabolisable protein (k values) depend on?

What is the number used for Australian systems?

Answer 11

• Will depend on how closely metabolisable protein matches protein required for maintenance, growth, milk etc.
• Australian system uses 0.7 for all functions except wool growth (0.6)
• Amino acid composition of MCP fairly constant
• MCP contributes most of metabolisable protein
• Lack of data to adopt different values for different functions

Question 12

Example of protein requirements (600 kg cow, 30 kg milk (32 g/kg protein), eating 19.3 kg (212 MJ ME) mixed diet)

KNOW THIS*******

look at lecture slides for assistance

Answer 12

Total 1327g/day is NET protein

Question 13

Example of protein requirements (600 kg cow, 30 kg milk (32 g/kg protein), eating 19.3 kg (212 MJ ME) mixed diet)

Dietary protein required (using SCA 1990)

Answer 13

So 1284 needs to be fed to meet production needs

the 0.7 in UDP bit is the efficiency

see lecture slides if needed

Question 14

Example of protein requirements (600 kg cow, 30 kg milk (32 g/kg protein), eating 19.3 kg (212 MJ ME) mixed diet)

Dietary CP required?

Look at lecture slides for assistance

Answer 14