L23: Dairy Cattle Feeding Standards: Energy

Question 1

What is energy required for maintenance?

Answer 1

• Mean steady state, no loss, no production
• Zero energy retention
• theoretically stable live weight
• British ARC system
• ME_M = 8.3 + 0.091W plus 5-10% for grazing

Question 2

Describe this equation

Answer 2

• #1 formula for ME requirement!!!!!!!
• IS IN THE EXAM
  KSM = 1.4 where:
  • K = 1 for sheep and goats; 1.2 for Bos indicus; 1.4 for Bos taurus
  • S = 1 for females and castrates; 1.15 for males
  • M = 1 + (0.23 x proportion of DE from milk) • W0.75 = Biological weight
  • A = Age in years (maximum 6)
  • Km = efficiency of ME utilisation for maintenance
  • MEp = ME used directly for production
  • MEgraze = Additional energy expenditure of grazing
  • ECold = Additional energy expenditure when temperature below thermal neutral zone

Question 3

Describe this equation:

Answer 3

Where:

• H = horizontal equiv. of distance walked in km
• C = 0.0025 for cattle, or 0.02 for sheep
• DMI = dry matter intake from pasture in kg/d
• D = dry matter digestibility as a proportion
• W = Weight

Question 4

Describe this equation

Milk Production

• EVL= (0.0381xF) + (0.0245xP) + (0.0165xL)

Answer 4

• Energy value of milk depends on components

• EVL= (0.0381xF) + (0.0245xP) + (0.0165xL)
• F = Fat content (g/kg)
• P = Protein content (g/kg)
• L = Lactose content (g/kg)
• Alternatives calculations:

• EVL= 0.0386F + 0.0205SNF - 0.236

• SNF = Solid non-fat concentrations (g/kg)

• EVL= 0.0458F + 1.222****

• KL = (0.02M/D) + 0.4 (or approx. 0.6)

• M/D = MJ ME/kg DM per Day

• MEL = Y x EVL /KL

• Where Y = Milk yield/day

Question 5

What is a standard reference weight (SRW)?

Answer 5

• Liveweight of an animal when skeletal development complete w/ a BC score of 3 (mid range)
• Brings all breeds to a common weight for inclusion in energy value (EB) calculations
• Used in the prediction of:
• composition of empty body gain (EBG)
• feed intake

Question 6

Describe how energy from liveweight loss can be used for lactation****

Answer 6

• transition state in cow preg=>lactating has largest e demand -this is wen LWL comes into play
• Net Energy in body tissue = 20MJ/kg (potential amount available)
• Used with 84% efficiency
• i.e. supplies 16.8MJ Net Energy
• This replaces 16.8/KL of dietary ME
• or about 28MJ ME for lactation
• Assuming efficiency of lactation 60%
• Net energy from LWL varies with condition
• **Calculated Net Energy in body tissue
• MJ/kg = 10.1 + 2.47CS**
• Higher the condition score = higher energy available from weight loss

Question 7

Describe this equation

Answer 7

• Z = W/SRW (Liveweight divided by Standard Reference Weight)
• R = [(0.92 x weight change/d)/(4SRWkg0.75)]-1

Question 8

What is the equation for ME_p (pregnancy)?

Answer 8

• ME_p = 1.13exp0.0106t

• t = days after conception
• Mainly used for dry cows and heifers

Question 9

What is the equation for dry matter intake capacity?
What is DMI influenced by?

Answer 9

Mid-late lactation

• DMI = 0.025W + 0.1Y

• Y = Milk yield (L/day)
• W = Weight (kg)
• Early lactation 2-3kg below this
• Influenced by
• size
• physiological state
• genotype
• digestibility
• substitution
• climate

Question 10

Solve this:
LEARN HOW TO DO IT. THIS QUESTION IS IN EXAM W/ DIFF FIGURES.!!!!!!

Housed 5 yr old 600kg cow producing 30kg milk/d (36g/kg butter fat (F); 86g/kg Solid non-fat conc. (SNF)) not pregnant and offered a diet of 11MJ/kg DM.

WHAT IS THE ENERGY REQUIREMENT?

Answer 10

look at lecture slides for assistance if necessary