Energy Requirements of Livestock

Energy Requirements of Livestock

Recommended Reading

• Chapter 10 in Pasture and Supplements for Grazing Animals by Rattray, Brookes, and Nicol (2007).

Learning Objectives

• Calculate the metabolisable energy (ME) requirements for ruminant animals.
• Describe factors affecting feed conversion efficiency, including:
  • Protein, Energy, Minerals, Vitamins.

Importance of Knowing Energy Requirements

• Animals need energy for survival and production.
• Enables effective feed planning (DM intake).
• Helps meet the genetic potential of animals.
• Identifies limiting nutrients for diet adjustments.

What is Metabolizable Energy (ME)?

• ME is the portion of feed energy available for:
  1. Maintenance
  2. Growth
  3. Reproduction
  4. Lactation
• ME is measured in heat units: joules, kilojoules, or megajoules.
  • 1 joule is slightly more than half a sugar crystal (0.102 mg/crystal).
  • Typical energy released as heat by a person at rest every 1/60 s.
• ME requirements:
  • Males: $0.35 \times kg^{0.75}$ = MJ BMR
  • Females: $0.30 \times kg^{0.75}$ = MJ BMR

Maintenance Requirements

• Account for more than half of energy needs (for average young adults).

Energy Expenditure

• A chart details kJ used per minute per kilogram of body weight for various activities (e.g., Badminton - 0.405 kJ/min/kg).
• To calculate energy expenditures:
  • Multiply the appropriate figure from the chart by body weight and duration of activity.

Calculate Your Maintenance Energy Requirements

• Activity Levels:
  • Inactive: 1.4 (sitting most of the day)
  • Light: 1.5 (some daily exercise)
  • Moderate: 1.78 (6 hours on feet)
  • Heavy: 2.1 (heavy laboring jobs)
• Select activity level and multiply by BMR.

Factors Affecting Energy Requirements for Maintenance

• Liveweight
• Age
• Gender
• Species
• Physiological state
• Activity
• Climate
• Feed quality

Basal Metabolic Rate (BMR)

• Influenced by:
  • Species (sheep > cattle)
  • Gender (males > females)
  • Age (young > old)
  • Liveweight (smaller animals > larger)
• Equation:
  • $MEm = species \times sex \times 0.28 \times EXP(-0.03 \times age) \times (lwt^{0.75}) / km$

Where is Energy Used in the Body?

• Main energy-users:
  • Liver
  • Brain
  • Heart
  • Kidneys
  • Muscles

Thermogenesis and Climate

• Ruminants maintain a constant body temperature of ~39°C.
• Heat production depends on food intake and nutrient efficiency.
• Thermoregulation methods:
  • In hot weather: sweating, panting, reduce intake.
  • In cold weather: insulation, increased intake, shelter.

Feed Intake Effects

• Energy requirements vary based on feed intake level.
• Higher quality feed increases efficiency of metabolizable energy.

K-values and Efficiency

• K represents energy lost as heat.
• Efficiency varies based on nutrients used:
  • Maintenance > Lactation > Growth
  • Factors affecting K-value impact feed conversion efficiency (FCE).
• Example values for K:
  • For maintenance: 0.70 (ruminant)
  • For lactation: 0.60
  • For growth: 0.50

Practice Calculations

1. Calculate MEm for a 480kg cow:

   • For high-quality pasture (NEm = 0.43 x LW^0.75 and km = 0.74):
     $MEm = \frac{0.43 \times 480^{0.75}}{0.74} = 59.6 \, \text{MJ ME/d}$

2. Calculate total ME requirements for lactating cow (producing 25L milk/day):

   • Total ME = MEm + MEL:
   • $MEL = \frac{(3.9 \times 25)}{0.63} = 154.8 \, \text{MJ ME/d}$
   • $Total ME = 59.6 + 154.8 = 214.4 \, \text{MJ ME/d}$

Summary

• Metabolizable energy requirements depend on net energy (NE) and efficiency of conversion (k-value).
• Total ME is the sum of ME for maintenance and production.
• High-quality feeds and production levels improve feed conversion efficiency (FCE).