AGSY102 - Lecture 9: Grazing

Learning Objectives
  • Describe main characteristics of grazing systems across Australian zones
  • Explain animal–pasture relationships
  • Identify common management practices
Australian Grazing Zones
  • Wheat–Sheep (mixed farming)
    • Area 32 M ha32\,\text{M ha}; rainfall 250!–!650 mm yr−1250!\text{–}!650\,\text{mm yr}^{-1}
    • Enterprises: crops + livestock (variable intensity)
  • Rangelands
    • Area >200\,\text{M ha}; arid / semi-arid
    • Extensive beef breeding; property size >10\,000\,\text{ha}
  • High-Rainfall Zone
    • Area 27 M ha27\,\text{M ha}; smaller farms 100!–!500 ha100!\text{–}!500\,\text{ha}
    • Intensive, premium livestock products
Key Regional Production Facts
  • NSW ≈ 20%20\% national beef / veal
  • QLD ≈ 50%50\% beef cattle
  • VIC = major dairy
  • WA = significant wool
Livestock Nutrient Requirements vs. Pasture Supply
  • Required: water, energy (carbohydrates & lipids), protein, minerals, vitamins
  • Principle of the primary limiting nutrient: performance capped by scarcest nutrient
  • Feed requirement varies with species, physiological stage, pasture quality
Pasture Quality
  • Metrics: digestibility %\%, metabolisable energy (ME, MJ kg−1\text{MJ kg}^{-1}), protein %\%
  • Quality declines with pasture maturity; sharper drop in tropical vs. temperate species
Pasture Quantity & Stocking Rate
  • Lower stocking → higher liveweight gain per head but lower gain per hectare
  • Heavy stocking degrades desirable species
Carrying Capacity
  • Definition: max livestock a land unit supports without degradation
  • Extensive: 0.2!–!2 DSE ha−10.2!\text{–}!2\,\text{DSE ha}^{-1}
  • Intensive: 15!–!25 DSE ha−115!\text{–}!25\,\text{DSE ha}^{-1}
  • Optimal zone balances individual gain, total production, economic return
Grazing Systems
  • Continuous: set-stocked; low infrastructure; relies on conservative stocking
  • Rotational: planned moves & rest periods; moderate infrastructure
  • Cell: many small paddocks; very short grazing; high management intensity
  • Strip: portable electric fence strips; moved 1–2× daily
  • System choice depends on rainfall reliability, pasture productivity, land capability, management capacity
Grazing Preferences by Species
  • Cattle: mostly grasses; prefer slopes <20\%
  • Sheep: select forbs; handle slopes ≤45%\le45\%
  • Goats: browse shrubs; highly agile
  • Mixed grazing (cattle + sheep/goats) can raise carrying capacity 15!–!20%15!\text{–}!20\% through complementary diets
Core Management Considerations
  • Climate & rainfall pattern
  • Soil fertility & constraints
  • Pasture species composition & growth phase
  • Matching stocking rate to carrying capacity
  • Infrastructure for chosen grazing system